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موضوع: آمپلیفایرها

  1. #21
    مدیر انجمن javad naderi آواتار ها
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    نقل قول نوشته اصلی توسط AWE نمایش پست ها
    اه ، آقای نادری شمایین ؟؟؟ بابا من فرزادم !!!
    چطورین ؟ چه خبر ؟
    سلام مرسی

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    AWE

  3. # ADS
    Circuit advertisement
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    Advertising world
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    Many
     

  4. #22
    عضو جدید
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    ببخشسد یه سوال داشتم ، تو یکی از انجمنا درباره افزایش برد ماژول HMTR بحث میکردن ، یکی از اعضا گفتن که میتونین از یه آمپلیفایر 1 تا 10 وات استفاده کنین اما خوب ، بحثشون دقیقا همون جا قطع شد و منم هرکاری کردم نتونستم باهاشون ارتباط برقرار کنم ...
    حالا ممنون میشم اگه کمکم کنین ، من یه فرستنده گیرنده رادیویی با برد حداقل یک کیلومتر میخوام با پروتکل ttl یا rs232 که تو ایران هم موجود باشه . هرچی گشتم چیز به دردبخوری پیدا نکردم بنابراین تصمیم گرفتم همین HMTR رو بردارم و با آمپلی فایر بردشو افزایش بدم ... حالا نمیدونم این روش عملی هست یا نه ! ممنون میشم کمکم کنید .

  5. #23
    کاربر علاقه مند
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    MSS
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    نقل قول نوشته اصلی توسط javad naderi نمایش پست ها
    مدار امپلی100وات ۸ اهم های فیدلتی ماسفت

    تو این مدار هم میتونین از ماسفت هم ازترانزیستور قدرت استفاده کنین(خود دانید!) راستی بیشتر از۴۵ولت هم دیگه بهش اعمال نکنینا!که وای به حالتون میشه.اگه مشکلی یا سوالی هم داشتین تونظرات مطرح کنین تا دراسرع وقت ژیگیری کنم.البته خودم هم چک میکنم





    ببخشید این کجاش ماسفت داره؟؟؟

  6. #24
    مدیر انجمن javad naderi آواتار ها
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    فکر کنم یک قسمت از شماتیک رو نزاشتن .

  7. #25
    مدیر انجمن javad naderi آواتار ها
    تاریخ عضویت
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    جواد نادری زاده
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    این مدار را برای کسانی آماده کردیم که با هیچ قدرت صدایی ارضاء نمی شوند . این مدار همانطور که می بینید با 1500 وات واقعی و امپدانس 4 اهم در خروجی مخصوص کسانی است که به اذیت و آزار همسایه ها علاقه دارند . چنین آمپلی فایر هایی در بازار در حدود 700 هزار تومان فروخته می شوند که معلوم هم نیست توان واقعی را اعلام می کنند ولی در این مدار ما با محاسبات به شما این مطلب را ثابت می کنیم . البته اگر به فکر این هستید چند ساعتی برای مراسمی مثل عروسی از این آمپلی فایر کار بکشید بهتر است از حالا در فکر یک رادیاتور مایع باشید . حتی اگر نمی خواهید این مدار را ببندید تا آخر مطلب با ما باشید زیرا هرچیزی که در الکترونیک خواندید در این مدار بطور عملی می بینید و یک تقویت کننده واقعی را با ما تحلیل خواهید کرد .
    توجه مهم : اگر دانش آموز هستید و یا در الکترونیک تازه کار هستید به هیچ وجه این مدار را به تنهایی تست نکنید زیرا با کوچکترین اشتباهی جریان بسیار بالای منبع تغذیه این مدار شما را در یک آن خشک می کند و ما هیچ مسئولیتی در قبال آن به عهده نمی گیریم . ضمنا مشکلات مداری از نظر کار ندادن و یا سوختن قطعات به ما مربوط نمی شود و هیچ سوالی در این زمینه را پاسخ نخواهیم داد .
    خیلی ها می پرسند که آیا با افزایش ولتاژ آمپلی فایر ها می توان توان را افزایش داد ؟ در پاسخ باید بگوییم خیر. هر نیمه هادی تا ولتاژ خاصی می تواند کار کند . برای مثال در این پروژه ما از ترانزیستور هایی که قادر است تا ولتاژ 250 ولت را تحمل کنند استفاده می کنیم .
    کسایی که کمی در الکترونیک وارد باشند ممکن است تا مدار را نگاه کنند بگویند چرا از Mosfet به جای ترانزیستور استفاده نکردید ؟ البته ماسفت ها تقویت خیلی خوبی دارند ولی ماسفت ها به خودی خود قیمت بالایی دارند . ماسفت ها دو نمونه عمودی و افقی دارند . نوع افقی در ولتاژ های بالای 200 ولت کمیاب هستند و در نوع عمودی مانند HEXFETs ها و مانند آنها نیز به خاطر اینکه تقویت این نوع ماسفت ها غیر خطی است به خوبی جریان های جزیی تقویت نمی شوند و شما مجبورید یک جریان ساکن با قدرت نسبی همیشه به آن بدهید که باعث اطلاف انرژی و افزایش حرارت شود و برای کاهش حرارت مجبورید از کلاس های ترانزیستوری استفاده کنید که کلی مدار شلوغ تر خواهد شد . و چندین مورد دیگر که در این بحث نمی گنجد . در صورتیکه در رابطه با Fet های جدید علاقه دارید مطالبی یاد بگیرید بهتر است در گوگل به زبان انگلیسی جستجو کنید زیرا متاسفانه در کتب آموزش و پرورش چیزی در این باره پیدا نخواهید کرد .
    تقویت کننده های تجاری دیگر که قدرتی در این حد دارند نیز از همین نوع طراحی استفاده نموده اند همچنین تقریبا همه از کلاس G برای محدود سازی اتلاف توان کلی منبع استفاده می کنند . در تمام این نوع آمپلی فایر ها نیز معمولا از منبع تغذیه سوئیچینگ استفاده شده است .
    نصب فن و یا رادیاتور در این مدار ضروری است زیرا در صورت آسیب دیدگی ترانزیستور ها تعمیر آن کمی مشکل و پر هزینه است زیرا ترانزیستور ها اکثر قابلمه ای هستند . پس یا از یک رادیاتور فن دار استفاده کنید یا اینکه از یک رادیاتور با مایه خنک کنند استفاده کنید .
    در مورد انتخاب اسپیکر هم خیلی باید دقت کنید زیرا این مدار حداقل 1500 وات تا 2 کیلو وات پیک به خروجی می دهد و اگر باند ضعیفی به آن متصل کنید منجر به پاره شدن باند می شود . در واقع اگر می خواهید از نظر محاسباتی به گفته ما برسید برای اینکه 1500 وات را کامل در خروجی داشته باشید باید 110 ولت را به یک باند 8 اهمی وصل کنید . همان طور که از فرمول توان به دست می آید :
    U2/R=P
    که 1512 وات را نتیجه می دهد . به نظر شما چنین باندی تا چند ثانیه دوام می آورد ؟ اگر می خواهید منظورم را بفهمید ترانس یک اسپیکر 100 وات را مشاهده کنید . حالا تصور کنید که 1500 وات شود . قبول دارم تصورش هم وحشتناکه چه ساب ووفر قدرتمندی می تواند به آمپلی فایر ما نصب گردد . البته کسی شما را مجبور نکرده صدا را تا آخر زیاد کنید . این مدار را می توان با ترفند هایی توانش را تا حدود 2200 هم رسانید ولی فکر نمی کنم بیشتر از این گوشی بتواند تحمل کند و دیوانگی می باشد . ولی اگر پول شما زیادی کرده و دوست دارید شیشه های اطراف را خورد کنید می توانید با اضافه کردن ترانزیستور ها بصورت موازی اهم خروجی را حتی به 2 اهم هم برسانید .
    خب بهتره شروع به طراحی مدار کنیم :
    می دانیم که توان خروجی 1.5 کیلو وات است و امپدانس خروجی 4 اهم است . طبق فرمول U2/R=P ما به 77.5V RMS نیاز داریم ولی کمی بیشتر از این ولتاژ باید در خروجی باشد زیرا ولتاژ خروجی با قرار گیری بار در خروجی کاهش می یابد همچنین مقداری از ولتاژ روی مقاومت امیتر ها تلف می شود . در نتیجه ولتاژ منبع تغذیه مورد نیاز ما برابر است با :
    VDC = VRMS * 1.414
    VDC = 77.5 * 1.414 = ±109.6V DC
    ما هنوز افت ولتاژ را در نظر نگرفته ایم ولی معمولا حدود 10 ولت هم برای افت ولتاژ ها قرار می دهند . ما برای اینکار از یک ترانسفورماتور 220 به 2x90 استفاده می کنیم که ولتاژ بدون بار ±130V DC را به مدار می دهد . همانطور که می بینید منبع تغذیه شما ولتاژ بسیار زیادی را دریافت می کند و اگر دست شما به این قسمت بر خورد کند حادثه بدی برای شما رخ می دهد .
    ما ولتاژ نهایی تغذیه را ±120V در نظر می گیریم زیرا حتی با بزرگترین ترانسفورمر ها و فیلتر های خازنی شما افت ولتاژ خواهید داشت . همچنین جریان مورد نیاز نیز بسیار حیرت آور است . با تقسیم کردن 110 ولت بر 4 اهم ولتاژ خروجی شما جریان 27.5A بر روی بار خواهید داشت . ولی جریان نامی اسپیکر ها زیر 20 آمپر در حالت ماکزیمم توان است . هر چیزی که در مورد تقویت کننده ها شما می دانستید را باید در این آمپلی فایر به روز کنید . با توجه به این جریان بالا فکر استفاده از خطوط PCB با ضخامت زیر 1.5 میلیمتر را از سر خود خارج کنید . در کل توصیه می شود از PCB استفاده نکنید . همچنین از سیم های زخیم استفاده کنید و به صد درصد مطمئن شوید جایی از مدار اتصال کوتاه ندارد زیرا اگر شما را نکشد کل ترانزیستور ها و سیم ها را می سوزاند . منبع تغذیه این مدار توانایی ذوب کردن سیم های نازک و PCB های باریک را دارد .
    مرحله بعدی بدست آوردن میزان اتلاف دقیق قطعات است . بدترین حالت اتلاف بار مقاومتی زمانی اتفاق می افتد که 1/2 ولتاژ تغذیه بین ترانزیستور و بار تقسیم شده است . در این حالت ولتاژ 65 ولت است که باعث یک توان آنی در بار و خروجی می شود . P = V² / R = 65² / 4 = 1056W
    این شروع کار است زیرا ما بایدیک محدوده مجاز را در نظر بگیریم . فراموش نکنید که ماکزیمم اتلاف در یک بار راکتیو با اختلاف فاز 45 درجه تقریبا دو برابر حساب می شود ، حدودا 1900W است . اگر ترانزیستور ها بتوانند در دمای 25 سالم بمانند خیلی خوب است ولی ما نیاز به تحمل بیشتر داریم . ما بین 9 قسمت خروجی تقسیم کردیم که حدود 212 وات به هر کدام خواهد رسید و برای دهمین قسمت هم از راه انداز استفاده شده . توجه کنید که با این همه توان حتما از هدسینگ همراه فن باید استفاده کرد .
    ترانزیستور MJ15024/5 و یا MJ21193/4 در بسته بندی های TO-3 می باشند و برای تحمل 250 وات در دمای 25 درجه طراحی شده اند .
    ترانزیستور راه انداز مقدماتی MJE340/350 بار گذاری را بر روی VAS یا (voltage amplification stage) کاهش می دهد . با این حال حدود 12 میلی آمپر از طریق VAS ، اتلاف 72 صدم وات می باشد .بنابراین Q4 , Q6 , Q9 و Q10 باید هدسینگ داشته باشند . همچنین Q5 باید تماس حرارتی با هدسینگ اصلی داشته باشد.
    مدار حفاظت کننده ، توان پیک ترانزیستور ها را به حدود 180 وات توسط یک اتصال کوتاه جریان 12 آمپری محدود می سازد .
    شماتیک شماره 1 برای وضوح بیشتر روی تصویر زیر کلیک کنید)

    بخش منبع تغذیه :
    منبع تغذیه مورد نیاز ما کمی بزرگ است . علت آن هم نیاز به یک ترانسفورماتور بسیار بزرگ است . زیرا این ترانسفورماتور حداقل باید 1KVA برای مدل 1.5kw دارد و برای مدل 2KW که صحبت شد نیاز به 1.5kVA دارید. چنین ترانسی در بازار گیر نمی آید و باید سفارش ساخت بدهید . مشکل بعدی فیلتر های خازنی هستند که باید 150 ولت باشند . و ممکن است به این آسانی بدست نیایند .
    مشکل بعدی احتمالا پیدا کردن پل دیود 35 آمپری است .

    مدار کنترل و حفاظت :

    این مدار بعد از رسیدن به دمای 35 درجه فن یا مایع کولینگ را در سیستم روشن می کند . سنسور حرارت می تواند ترانزیستور یا یک دما سنج باشد .
    این مطلب به طور اختصاصی توسط تکنو الکترو نوشته شده است لطفا برای حمایت از ما و قرار گرفتن مطالب مفید بیشتر بعد از کپی برداری منبع را ذکر کنید .

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  9. #26
    مدیر انجمن javad naderi آواتار ها
    تاریخ عضویت
    Jan 2011
    نام
    جواد نادری زاده
    نوشته ها
    830
    تشکر
    225
    تشکر شده 1,334 بار در 602 پست

    پیش فرض

    In various parts of The Audio Pages, I have said that I am not a fan of MOSFET power amplifiers. Well, this amp has changed my views, and I consider this to be a "reference" system in all respects. The performance is extremely good, with vanishingly low distortion levels, plenty of power, very wide full power bandwidth, and the "self protecting" nature of the MOSFETs themselves.
    This is not to suggest that the amp is indestructible (no amplifier can make that claim successfully), but it is much more tolerant of faults than a bipolar transistor amp, and requires nothing more than a pair of zener diodes to limit the current. Having said that, I would still recommend that you avoid shorted output leads and the like - i.e. Don't push your luck ;-)
    One thing that has emerged that is absolutely critical is the PCB layout. The layout of this new amplifier is similar to that used for the P68 Subwoofer amplifier, and this has some major benefits. P68 has no right to sound as good as it does, and although designed for subwoofer use, it has proven during listening and testing to be a very low distortion design - despite the Class-B output stages. All PCB tracks in the input and driver section are as short as possible, minimising the chance of noise pickup from other sections of the circuit.
    This amplifier is designed to be as flexible as possible, with no bad habits. Indeed, it will operate stably with supply voltages as low as +/-5V (completely pointless, but interesting), all the way to the maximum supply voltage of +/-70V. The only change that is needed is to trim the MOSFET bias pot!
    With the full supply voltage of +/-70V (which must not be exceeded!), RMS power is around 180W into 8 ohms, or 250W into 4ohms. Short term (or "music") power is typically about 240W into 8 ohms and 380W into 4 ohms. Note that depends to a very great degree on the power supply, and a very robust supply is an absolute requirement for the maximum output.
    In general, unless you really need the maximum possible power, I suggest that you limit the supply voltage to ±56V using a 40+40V transformer. You will get around 150W into 8 ohms from this supply voltage (short-term), but you also relax the demands placed on the MOSFETs and heatsinks.
    Since this amp probably has more power than you will normally ever need, even if you do skimp a little on the transformer, the loss will be very small.
    It is worth noting that a MOSFET amp will always produce less power than a bipolar transistor version using the same supply voltage. Even using an auxiliary supply will make only a small difference (one reason I elected not to add the extra complexity). A bipolar design using a ±70V supply can be expected to produce something in the order of 270W into 8 ohms, and well over 500W into 4 ohms. The specified MOSFETs have a rated Vds (saturated voltage, Drain to Source) of 12V at full current, and that is simply subtracted from the DC value of the supply voltage. Using the same ±70V supply with a MOSFET amp will give less power than quoted above (see below for measured figures).

    Photograph of Completed Amplifier Board (Early Version) The photo shows the simplicity of the PCB. The MOSFETs are mounted below the board, and are bolted down in the same way as with the P3A and P68 boards. No other mounting is needed. PCB pins are used as anchor points for the power ground link (the green wire along the front edge), so that the main current carrying tracks were not compromised by running a separate track (which would have required a reduction in size of the positive supply rail).
    The entire front-end section is between the electrolytic caps, and is deliberately as compact as possible. This improves performance, by ensuring that there are no long tracks for the input stage, which will pick up noise and can seriously degrade the sound of the amplifier.
    Performance Figures The performance of this amp is such that many measurements are very difficult. Some of the more basic measurements are as shown below, based on my custom made transformers which provide ±65V unloaded ...
    ParameterMeasurementConditions Output Power> 180W< 1% THD, 8Ω
    > 275W< 1% THD, 4Ω DC Offset< 20mVTypical Noise< 2mV RMSUnweighted (-54dBV) THD0.015%No load, 30V RMS output, 1kHz
    0.017%8 Ohms, 30V RMS output, 1kHz
    0.02%4 Ohms, 30V RMS output, 1kHz Output Impedance< 10 mΩ1kHz, 4Ω load
    < 25 mΩ10kHz, 4Ω load Frequency Response10Hz to 50kHzAt 1W, -1.5dB Basic Performance Figures In particular, the distortion figures show that amp loading causes only very small variations, with any harmonics being predominantly from my audio oscillator. There are no visible or audible high order components to the distortion waveform. Output impedance was measured on a fully built amplifier, including the internal wiring. This entails around 200mm of wire in all (per channel), so the output impedance of the amplifier itself is obviously lower than quoted. For an 8 ohm load, the damping factor at 1kHz is around 800 (8 / 10 milliohms) - completely pointless of course, since any speaker lead will ruin that very quickly.
    Noise was measured with inputs open-circuited, and at -54dBV may not look too wonderful, however this figure is very pessimistic. Remember that this is the unweighted measurement, with bandwidth extending to well in excess of 100kHz. Even so, signal to noise ratio (referred to full power) is 86dB unweighted, and the amp is completely silent into typical speakers. Indeed, even connecting a pair of headphones directly to the amp outputs revealed that no noise was audible. Naturally, your methods of construction will differ from mine, and you may not be able to get the same performance.
    Intermodulation distortion cannot be measured with the equipment I have available, but I have included a screen capture of the three measurements I took. Most of the harmonic content visible (not that there is a great deal anyway) is present in the two generators I used, and the amplifier contributes virtually nothing.

    1kHz + 2kHz at +30dBV Output (8Ω)


    1kHz + 2kHz at -25dBV Output (8Ω)


    10kHz + 12kHz at +20dBV Output (8Ω)
    Click on any of the images above for a full resolution version.
    Description The very first thing you will notice is that I have broken with tradition with this amp, and there are no component values shown. Given the performance of the circuit, and the fact that I have already sold a couple as completed, finished amplifiers, I am not about to give away all my secrets for the design. If you want the component values, you must purchase the PCB. There are no exceptions, so don't ask.
    The schematic of the amp is shown in Fig. 1, and it is about as simple as a high power MOSFET amplifier can get - it is considerably simpler than most, but lacks nothing in performance. The circuit diagram belies the ability of the amplifier though, so do not be tempted to think that it cannot perform as well as more complex designs - it does, and exceeds the performance of many (if not most) of them. It will be seen that I elected to use a bootstrap current source rather than an active version - there is negligible cost difference, but I was unwilling to make such a radical change after testing the prototype and being so impressed with the results. (If it ain't broke, don't fix it!)
    The front end is a conventional long-tailed pair (LTP) using a current mirror load and an active current sink in the "tail". Interestingly, adding the current mirror made no difference to distortion, but reduced the DC offset to less than 25mV. The improvement was such that I elected to retain the mirror.
    In tests thus far (both measurement and listening), I have been unable to detect even a hint of what is commonly referred to as the "MOSFET sound". The relatively high levels of low order distortion and susceptibility to crossover (or "notch" distortion that plague many MOSFET designs are completely missing - indeed, even with zero bias on the MOSFETs, crossover distortion below 10kHz is barely measurable, let alone audible!
    Note Carefully:
    The most critical aspect of the design is the PCB layout, and it is very doubtful that if you make your own board, that you will get performance even approaching mine. Power output is essentially unchanged, but distortion and stability are achieved by a compact and carefully designed layout for the front end and driver circuits, which minimises any adverse PCB track coupling that causes much higher distortion levels, and may cause oscillation.
    This is not a ploy on my part to get people to purchase my PCBs - that has already been taken care of by leaving out the component values. The simple fact is that unless the PCB layout is done with the utmost care, any amplifier can be made to have far greater distortion levels and reduced stability margins than the published figures suggest.
    Low Power Version
    As shown in the schematics below (figures 1 and 2), the amplifier can be made in high or low power version, and although there is a bit of vacant PCB real estate in the low power design, it is significantly cheaper to make and will be more than sufficient for most constructors. If this version is built (using only 1 pair of MOSFETs), it is essential to limit the supply voltage to +/-56V so that it can drive both 4 and 8 ohm loads without excess dissipation. With this voltage, expect about 100W continuous into 8 ohms, and around 150W into 4 ohms. Naturally, dual MOSFET pairs may be used at this voltage as well, providing much better thermal performance (and therefore cooler operation), far greater peak current capability and slightly higher power. This version may be used at any voltage from +/-25V to +/-42V.

    Figure 1 - Standard (Low Power) Version The MOSFETs used are Hitachi lateral devices, 2SK1058 (N-Channel) and 2SJ162 (P-Channel). These are designed specifically for audio, and are far more linear than the (currently) more common switching devices that many MOSFET amps use. Unfortunately, they are not especially cheap, but their performance in an audio circuit is so much better than vertical MOSFETs, HEXFETs, etc., that there is no comparison. Note that using HEXFETs or any other vertical MOSFET type is not an option. They will fail in this circuit, as it was not designed to use them.
    An alternative (and possibly marginally better than the 2SK/2SJ series) is the Exicon ECX10N20 and ECX10P20 (available from Profusion PLC in the UK). These have been used in most of the amps I have built, and they work very well. So potential constructors can verify that the semiconductors are available before purchasing a PCB, this information has now been included. All other parts are quite standard.
    High Power Version
    The same PCB is used, but has an extra pair of MOSFETs. Since the devices are running in parallel, source resistors are used to force current sharing. Although these may be replaced by wire links, I do not recommend this. This version may be operated at a maximum supply voltage of +/-70V, and will give up to 180W RMS into 8 ohms, and 250W into 4 ohms. Short term (peak) power is around 240W into 8 ohms and 380W into 4 ohms. These figures are very much dependent on your power supply regulation, determined by the VA rating of the transformer, size of filter caps, etc.

    Figure 2 - High Power Version Although not shown, the transistors and MOSFETs are the same in this version as for the low power variant. The additional capacitors (C11 and C12) shown are to balance the gate capacitance. The P-Channel MOSFETs have significantly higher gate capacitance than their N-Channel counterparts, and the caps ensure that the two sides of the amp are roughly equal. Without these caps, the amp will almost always be unstable.
    As noted above, the PCB is the same for both versions, but for Fig. 2 it is fully populated with 2 pairs of power MOSFETs. The high power version may also be used at lower supply voltages, with a slight increase in power, but considerably lower operating temperatures even at maximum output, and potentially greater reliability.
    With both versions, the constructors' page gives additional information, and the schematics there include an enhanced Zobel network at the output for greater stability even with the most difficult load. This is provided for on the PCB, and allows the amp to remain stable under almost any conditions.
    The entire circuit has been optimised for minimum current in the Class-A driver, while still providing sufficient drive to ensure full power capability up to 25kHz. The slew rate is double that required for full power at 20kHz, at 15V/us, and while it is quite easy to increase it further, this amp already outperforms a great many other amps in this respect, and faster operation is neither required nor desirable.
    Note - There are actually two caps marked C5, and two marked C6. This is what is on the PCB overlay, and naturally was not found until it was too late. Since these caps cannot be mixed up, it will not cause a problem.
    In both versions of the amp, R7 and R8 are selected to provide 5mA current through the voltage amplifier stage. You will need to change the value to use a different supply voltage ...
    R7 = R8 = Vs / 10 (k) (Where Vs is one supply voltage only)
    For example, to set the correct current for ±42V supplies ...
    R7 = R8 = 42 / 10 = 4.2k (use the next lower standard value - 3.9k)
    Construction As suggested above, I strongly recommend that you purchase the PCB for this amplifier, or you will almost certainly get results that are nowhere near the amp's real ability. The PCB also makes construction a breeze, with everything except the power supply mounted on the board itself. Like many other ESP power amps, the MOSFETs are mounted underneath the board, requiring only two (or four) screws to attach the PCB and output devices. As always, full construction details will be available in the ESP secure site when you purchase the board(s).
    The suggested power supply is completely conventional. Although a small amount of additional power can be obtained by using an auxiliary supply (to boost the rail voltage for the MOSFET drive stage), this is at the expense of greater complexity and more things to go wrong. The transformer for the supply should be matched to the expected power you wish to obtain from the amp. The following table shows the recommended transformer voltage and VA rating for a single channel - either use two transformers or a single unit with twice the VA rating shown for stereo.
    AC VoltsDC VoltsVAPower (8Ω) 20-0-20+/-28V10040 25-0-25+/-35V10050 30-0-30+/-4216080 40-0-40+/-56V200150(Recommended Supply Voltage) 50-0-50+/-70V300240
    Note that all powers shown are "short term" or peak - continuous power will always be less as the supply collapses under load. Peak power levels are usually achieved (or approached) with most music because its transients are generally between 6dB and 10dB greater than the average power output. Transformer VA ratings shown are a guide only - larger or smaller units may be used, with a marginal increase or reduction of peak power. Always use at least the size shown for subwoofer use! Values in bold are preferred, and will give enough power for most systems along with optimum reliability and low operating temperature.

    Figure 3 - Power Supply Circuit Diagram Figure 3 shows the power supply circuit diagram for a ±56V supply, and there is nothing new about it. As I always recommend, the bridge rectifier should be a 400V/35A chassis mount type, and should be properly chassis mounted using heatsink compound.
    Filter capacitors must be rated to at least the nominal supply voltage, and preferably higher. If possible, use 105°C rated caps, and join the earthed terminals very solidly to form the star earthing point.
    Note - The fuse should be selected according to the size of the power transformer. For any toroidal transformer over 300VA, a soft start circuit is highly recommended. Use the transformer manufacturer's suggested fuse - if this information is not available, ask the supplier - not me!
    The DC supply must be taken from the capacitor terminals - never from the bridge rectifier. Using several small capacitors will give better performance than a single large one, and is usually cheaper as well. For example, the performance of 10 x 1,000uF capacitors is a great deal better (in all respects) than a single 10,000uF cap, at between 50% to 70% of the cost of the large unit. This lunch is not free, but it is heavily discounted
    When you purchase the PCB, you will not only get all component values, but will also have access to information for a power supply that is optimised for the best possible performance for a conventional supply. There is nothing especially innovative about the "advanced" supply schematic, but the overall results will surprise you.

  10. #27
    مدیر انجمن javad naderi آواتار ها
    تاریخ عضویت
    Jan 2011
    نام
    جواد نادری زاده
    نوشته ها
    830
    تشکر
    225
    تشکر شده 1,334 بار در 602 پست

    پیش فرض

    Introduction There are some important updates to this project, as shown below. Recent testing has shown that with the new ON Semi transistors it is possible to obtain a lot more power than previously. The original design was very conservative, and was initially intended to use 2SA1492 and 2SC3856 transistors (rated at 130W) - with 200W (or 230W) devices, some of the original comments and warnings have been amended to suit.
    Updates
    30 Jul 2003
    - OnSemi has just released a new range of transistors, designed specifically for audio applications. These new transistors have been tested in the P68, and give excellent results. As a result, all previous recommendations for output transistors are superseded, and the new transistors should be used. The output devices are MJL4281A (NPN) and MJL4302A (PNP), and feature high bandwidth, excellent SOA (safe operating area), high linearity and high gain. Driver transistors are MJE15034 (NPN) and MJE15035 (PNP). All devices are rated at 350V, with the power transistors having a 230W dissipation and the drivers are 50W.
    23 Sept 2003 - The new driver transistors (MJE15034/35) seem to be virtually impossible to obtain - ON Semi still has no listing for them on the website. The existing devices (well known and more than adequate) are MJE15032 (NPN) and MJE15033 (PNP), and these will substitute with no problems at all. It is also possible to use MJE340 and MJE350 as originally specified (note that the pinouts are reversed between the TO-126 and TO-220 devices).
    Note that some component values have been changed! The layout is the same, but the changes shown will reduce dissipation in Q7 and Q8 under light load conditions.
    Having built a couple of P68 amps using these transistors, I recommend them highly - the amplifier is most certainly at its very best with the high gain and linearity afforded by these devices. Note that there are a few minor changes to the circuit (shown below).
    With ±70V supplies, the input and current source transistors must be MPSA42 or similar - the original devices shown will fail at that voltage! Note that the MPSA42 pinout is different from the BC546s originally specified. Full details of transistor pinouts are shown in the construction article (available to PCB purchasers only).
    High power amps are not too common as projects, since they are by their nature normally difficult to build, and are expensive. A small error during assembly means that you start again - this can get very costly. I recommend that you use the PCB for this amplifier, as it will save you much grief. This is not an amp for beginners working with Veroboard!
    The amplifier can be assembled by a reasonably experienced hobbyist in about three hours. The metalwork will take somewhat longer, and this is especially true for the high continuous power variant. Even so, it is simple to build, compact, relatively inexpensive, and provides a level of performance that will satisfy most requirements.
    WARNINGS:

    • This amplifier is not trivial, despite its small size and apparent simplicity. The total DC is over 110V (or as much as 140V DC!), and can kill you.
    • The power dissipated is such that great care is needed with transistor mounting.
    • The single board P68 is capable of full power duty into 4 Ohm loads, but only at the lower supply voltage.
    • For operation at the higher supply voltage, you must use the dual board version.
    • There is NO SHORT CIRCUIT PROTECTION. The amp is designed to be used within a subwoofer or other speaker enclosure, so this has not been included. A short on the output will destroy the amplifier.

    DO NOT ATTEMPT THIS AMPLIFIER AS YOUR FIRST PROJECT Description Please note that the specification for this amp has been upgraded, and it is now recommended for continuous high power into 4 Ohms, but You will need to go to extremes with the heatsink (fan cooling is highly recommended). It was originally intended for "light" intermittent duty, suitable for an equalised subwoofer system (for example using the ELF principle - see the Project Page for the info on this circuit). Where continuous high power is required, another 4 output transistors are recommended, wired in the same way as Q9, Q10, Q11 and Q12, and using 0.33 ohm emitter resistors.
    Continuous power into 8 ohms is typically over 150W (250W for ±70V supplies), and it can be used without additional transistors at full power into an 8 ohm load all day, every day. The additional transistors are only needed if you want to do the same thing into 4 ohms at maximum supply voltage! Do not even think about using supplies over ±70V, and don't bother asking me if it is ok - it isn't!
    The circuit is shown in Figure 1, and it is a reasonably conventional design. Connections are provided for the Internal SIM (published elsewhere on the Project Pages), and filtering is provided for RF protection (R1, C2). The input is via a 4.7uF bipolar cap, as this provides lots of capacitance in a small size. Because of the impedance, little or no degradation of sound will be apparent. A polyester cap may be used if you prefer - 1uF with the nominal 22k input impedance will give a -3dB frequency of 7.2Hz, which is quite low enough for any sub.

    Figure 1 - Basic Amplifier Schematic The input stage is a conventional long-tailed pair, and uses a current sink (Q1) in the emitter circuit. I elected to use a current sink here to ensure that the amp would stabilise quickly upon application (and removal) of power, to eliminate the dreaded turn on "thump". The amp is actually at reasonably stable operating conditions with as little as +/-5 volts! Note also that there are connections for the SIM (Sound Impairment Monitor), which will indicate clipping better than any conventional clipping indicator circuit. See the Project Pages for details on making a SIM circuit. If you feel that you don't need the SIM, omit R4 and R15.
    The Class-A driver is again conventional, and uses a Miller stabilisation cap. This component should be either a 500V ceramic or a polystyrene device for best linearity. The collector load uses the bootstrap principle rather than an active current sink, as this is cheaper and very reliable (besides, I like the bootstrap principle :-)
    All three driver transistors (Q4, 5 & 6)must be on a heatsink, and D2 and D3 should be in good thermal contact with the driver heatsink. Neglect to do this and the result will be thermal runaway, and the amp will fail. For some reason, the last statement seems to cause some people confusion - look at the photo below, and you will see the small heatsink, 3 driver transistors, and a white "blob" (just to the left of the electrolytic capacitor), which is the two diodes pressed against the heatsink with thermal grease.

    C11 does not exist on this schematic, so don't bother looking for it. It was "mislaid" when the schematic was prepared, and I didn't notice until someone asked me where and what it was supposed to be. Sorry about that. It is in the output stage that the power capability of this amp is revealed. The main output is similar to many of my other designs, but with a higher value than normal for the "emitter" resistors (R16, R17). The voltage across these resistors is then used to provide base current for the main output devices, which operate in full Class-B. In some respects, this is a "poor-man's" version of the famous Quad current dumping circuit, but without the refinements, and in principle is the same as was used in the equally famous Crown DC300A power amps.
    Although I have shown MJL4281A and MJL4302A output transistors, because they are new most constructors will find that these are not as easy to get as they should be. The alternatives are MJL3281/ MJL1302 or MJL21193/ MJL21194.
    Note: It is no longer possible to recommend any Toshiba transistors, since they are the most commonly counterfeited of all. The 2SA1302 and 2SC3281 are now obsolete - if you do find them, they are almost certainly fakes, since Toshiba has not made these devices since around 1999~2000.
    Use a standard green LED. Do not use high brightness or other colours, as they may have a slighty different forward voltage, and this will change the current sink's operation - this may be a miniature type if desired. The resistors are all 1/4W (preferably metal film), except for R10, R11 and R22, which are 1W carbon film types. All low value resistors (3.3 ohm and 0.33 ohm) are 5W wirewound types.
    Because this amp operates in "pure" Class-B (something of a contradiction of terms, I think), the high frequency distortion will be relatively high, and is probably unsuited to high power hi-fi. At the low frequency end of the spectrum, there is lots of negative feedback, and distortion is actually rather good, at about 0.04% up to 1kHz. My initial tests and reports from others indicate that there are no audible artefacts at high frequencies, but the recommendation remains.
    Power Dissipation Considerations
    I have made a lot of noise about not using this amp at ±70V into 4 ohms without the extra transistors. A quick calculation reveals that when operated like this, the worst case peak dissipation into a resistive load is 306W (4Ω/ ±70V supplies). The four final transistors do most of the work, with Q7 and Q8 having a relatively restful time (this was the design goal originally). Peak dissipation in the 8 output devices is around 70W each.
    Since I like to be conservative, I will assume that Q7 and Q8 in the updated schematic shown contribute a little under 1A peak (which is about right). This means that their peak dissipation is around 18W, with the main O/P devices dissipating a peak of 70W each. The specified transistors are 230W, and the alternatives are 200W, so why are the extra transistors needed?
    The problem is simple - the rated dissipation for a transistor is with a case temperature of 25°C. As the amp is used, each internal transistor die gets hot, as does the transistor case - the standard derating curves must be applied. Add to this the reactive component as the loudspeaker drives current back into the amp (doubling the peak dissipation), and it becomes all too easy to exceed the device limits. The only way that this amp can be used for continuous high power duty with ±70V supplies and a 4Ω loudspeaker load is to keep the working temperature down to the absolute minimum - that means four output devices per side, a big heatsink and a fan!

    Figure 1a - Double Output Stage
    Figure 1A shows the doubled output stage, with Q9, Q10, Q11 and Q12 simply repeated - along with the emitter resistors. Each 1/2 stage has its own zobel network and bypass caps as shown, as this is the arrangement if the dual PCB version is built. When you have this many power transistors, the amp will happily drive a 4 ohm load all day from ±70V - with a big enough heatsink, and forced cooling. Over 500W is available, more than enough to cause meltdown in many speakers!
    A Few Specs and Measurements
    The following figures are all relative to an output power of 225W into 4 ohms, or 30V RMS at 1kHz, unless otherwise stated. Noise and distortion figures are unweighted, and are measured at full bandwidth. Measurements were taken using a 300VA transformer, with 6,800uF filter caps.
    Mains voltage was about 4% low when I did the tests, so power output will normally be slightly higher than shown here if the mains are at the correct nominal voltage. Figures shown are measured with ±56V nominal, with the figure in (brackets) estimated for ±70V supplies.


    Voltage Gain27dB27dB Power (Continuous)153W (240W)240W (470W) Peak Power - 10 ms185W (250W)344W (512W) Peak Power - 5 ms185W (272W)370W (540W) Input Voltage1.3V (2.0V) RMS1.3V (2.0V) RMS Noise *-63dBV (ref. 1V)-63dBV (ref. 1V) S/N Ratio *92dB92dB Distortion0.4%0.4% Distortion (@ 4W)0.04% (1 Khz)0.04% (1 Khz) Distortion (@ 4W)0.07% (10 kHz)0.07% (10 kHz) Slew Rate> 3V/us> 3V/us
    * Unweighted
    These figures are quite respectable, especially considering the design intent for this amp. While (IMO) it would not be really suitable for normal hi-fi, even there it is doubtful that any deficiencies would be readily apparent, except perhaps at frequencies above 10kHz. While the amp is certainly fast enough (and yes, 3V/us actually is fast enough - response extends to at least 30kHz, but not at full power), the distortion may be a bit too high.
    Note that the "peak power" ratings represent the maximum power before the filter caps discharge and the supply voltage collapses. I measured these at 5 milliseconds and 10 milliseconds. Performance into 4 ohm loads is not quite as good, as the caps discharge faster. The supply voltage with zero power measured exactly 56V, and collapsed to 50.7V at full power into 8 ohms, and 47.5V at full power into 4 ohms.

    Photo of Completed Prototype
    The photo does not show the silk screened component overlay, since this is the prototype board. The final boards have the overlay (as do all my other boards). The observant reader will also see that the 5W resistor values are different from those recommended - this was an early prototype using 130W transistors.
    As can be seen, this is the single board version. The driver transistors are in a row, so that a single sheet aluminium heatsink can be used for all three. Holes are provided on the board so the driver heatsink can be mounted firmly, to prevent the transistor leads breaking due to vibration. This is especially important if the amp is used for a powered subwoofer, but will probably not be needed for a chassis mounted system.
    The driver and main heatsinks shown are adequate for up to 200W into 4 ohms with normal program material. The power transistors are all mounted underneath the board, and the mounting screw heads can be seen on the top of the board.
    Deceptively simple, isn't it?
    Power Supply

    WARNING: Mains wiring must be performed by a qualified electrician - Do not attempt the power supply unless suitably qualified. Faulty or incorrect mains wiring may result in death or serious injury. The basic power supply is shown in Figure 2. It is completely conventional in all respects. Use a 40-0-40 V transformer, rated at 300VA for normal use. For maximum continuous power, a 50-0-50V (500VA or more) transformer will be needed. This will give a continuous power of about 450W, and peak power of over 500W is possible with a good transformer. Remember my warnings about using the amp in this way, and the need for the additional output transistors, big heatsink and fan.

    Figure 2 - Basic Power Supply Circuit
    For 115V countries, the fuse should be 6A, and in all cases a slow blow fuse is required because of the inrush current of the transformer. For anything above 300VA, a soft-start circuit is highly recommended (see Project 39).
    The supply voltage can be expected to be higher than that quoted at no load, and less at full load. This is entirely normal, and is due to the regulation of the transformer. In some cases, it will not be possible to obtain the rated power if the transformer is not adequately rated.
    Bridge rectifiers should be 35A types, and filter capacitors must be rated at a minimum of 63V (or 75V if you use 70V supplies). Wiring needs to be heavy gauge, and the DC must be taken from the capacitors - not from the bridge rectifier.
    Although shown with 4,700uF filter capacitors, larger ones may be used. Anything beyond 10,000uF is too expensive, and will not improve performance to any worthwhile degree. Probably the best is to use two 4,700uF caps per side (four in all). This will actually work better than a single 10,000uF device, and will be cheaper as well.
    NOTE: It is essential that fuses are used for the power supply. While they will not stop the amp from failing (no fuse ever does), they will prevent catastrophic damage that would result from not protecting the circuit from over-current conditions. Fuses can be mounted in fuseholders or can be inline types. The latter are preferred, as the supply leads can be kept as short as possible. Access from outside the chassis is not needed - if the fuses blow, the amplifier is almost certainly damaged.

  11. #28
    مدیر انجمن javad naderi آواتار ها
    تاریخ عضویت
    Jan 2011
    نام
    جواد نادری زاده
    نوشته ها
    830
    تشکر
    225
    تشکر شده 1,334 بار در 602 پست

    پیش فرض

    Introduction Update - 25 June 2009 - Although the last update highly recommended the latest OnSemi power and driver transistors, they remain hard to get in most countries. As a result, the recommended power transistors are now the much more readily available MJL21193/4. While in theory these are not quite as good as the latest versions, they are still excellent devices. It is extremely doubtful that anyone would ever pick any difference with test instruments, and there will be no change that is audible.
    Much the same applies to the driver transistors. Although the BD139/140 devices are not considered to be the "finest" audio transistors available, they work very well indeed, and have been used in all of the P3A amps I've built for my own use or as part of a system. Again, it is highly unlikely that there will be any meaningful measurement that will show these transistors to be inferior to "audiophile" parts.
    24 Jul 2003. - OnSemi released a new range of transistors, designed specifically for audio applications. These new transistors have been tested in the P3A, and give excellent results. As a result, all previous recommendations for output transistors are superseded, and the new transistors should be used ... if you can get them. Six years after release, the new devices are still not readily available.
    The output devices are MJL4281A (NPN) and MJL4302A (PNP), and feature high bandwidth, excellent SOA (safe operating area), high linearity and high gain. Driver transistors are MJE15034 (NPN) and MJE15035 (PNP). All devices are rated at 350V, with the power transistors having a 230W dissipation and the drivers are 50W.
    The basis for this amplifier was originally published as Project 03, and although the base design is almost 30 years old, as an amplifier it remains "state of the art" - this is an extremely good amplifier. It is simple to build, uses commonly available parts and is stable and reliable. The design featured is a full update on the original project, and although it has many similarities, is really a new design.
    This new amp (like the original) is based on an amp I originally designed many years ago, of which hundreds were built. Most were operated as small PA or instrument amps, but many also found their way into home hi-fi systems. The amp is perfectly capable of driving 4 Ohms, provided the supply voltage is maintained at no more than ±35V.
    This amplifier, although very simple, is capable of superb performance. This is not an amp to be under estimated, as the sonics are very good indeed, and this is due (in part, at least) to the inherent simplicity of the design. The amp is exceptionally quiet, and is reasonably tolerant of difficult loads. It is an ideal amplifier for biamped systems, and may be operated in bridge mode (BTL) if you use the recommended output transistors (which have the necessary power ratings).

    The design has had the benefit of many, many years of consistent use, and this version is the best of all - the refinements ensure minimum "switch on" or "switch off" noise, and the availability of really good output devices has improved on a known and very stable design.

    I have heard nothing but praise from those who have built this amplifier - all feedback I have received has been very positive indeed. The sound quality is up there with the very best. Highly recommended !
    A reader has constructed a site based on the assembly of the P3A amp, and he has some useful information that will be helpful for anyone else looking for equivalent transistors, design guides, etc. Although considerable effort went into the site, it is unfortunately no longer on-line.
    Description Note that like the original, there is (still) no output short circuit protection, so if speaker leads are shorted while the amp is working with a signal, there is a very real risk of the transistors being destroyed. I suggest and recommend the use of Speakon connectors both at the amplifier and speaker ends. The specifications are very similar to those of the original project, but the use of a current sink in the differential pair input stage means that there is virtually no thump at turn on or off.
    I have also added the ability to adjust the quiescent current, and with the transistors specified the amp will provide 100W into 8 ohms, at a maximum supply voltage of ±42V. This supply is easily obtained from a 30-0-30V transformer.

    Figure 1 - Amplifier Schematic As can be seen, it is not a complex amp, but the performance is excellent. Connections are provided for a SIM (Sound Impairment Monitor), and there is also a resistor (R17) added to allow bridging. This resistor connects to the output of the other amplifier (the master). When used in this way, the input should be grounded - do not omit the capacitor, or DC offset will be too high. When used in bridge mode (also called BTL - Bridge Tied Load), the SIM should be taken from the master amplifier only.
    * Components marked thus are optional - if you do not want to use the SIM or bridging, these may be omitted completely.
    For use into 4 ohms (including bridging into 8 ohm loads), do not exceed ±35V (from a 25-0-25V transformer). Most applications will be satisfied with the lower voltage, and the reliability of the amp is assured with almost any load. In bridge mode, this amp will happily produce 200W into 8 ohms, and will do so reliably even for continuous high power levels. Never attempt to operate the amp in bridge mode into 4 ohms, as this represents an equivalent load to each amp of 2 ohms. The amp was not designed to handle this, and will fail. ±42V is the absolute maximum voltage, and should only be used where 4 ohm loads will never be applied.
    D1 is a green LED, and should be a standard type. Don't use a high brightness LED, or change the colour. This is not for appearance (although the green LED looks pretty neat on the board), but for the voltage drop - different coloured LEDs have a slightly different voltage drop.
    VR1 is used to set the quiescent current, and normally this will be about 50-100mA. The amp will work happily at lower current, but the distortion starts to be noticeable (on a distortion meter monitored by an oscilloscope) at less than around 20mA (the recommended minimum quiescent current). The Class-A driver (Q4) has a constant current load by virtue of the bootstrap circuit R9, R10 and C5. Stability is determined by C4, and the value of this cap should not be reduced. With fast output transistors such as those specified, power bandwidth exceeds 30kHz.
    With the suggested and recommended 35V supplies, Q4 and the output drivers (Q5 and Q6) will normally not require a heatsink. With 4 ohm loads, you may find that a heatsink for Q5 and Q6 is needed, but my experience is that these transistors should not get hot under most operating conditions.
    If using the amp at ±42V, a small heatsink should be used for Q4, as the dissipation will be quite a bit higher and the device will get very warm.
    Although I have shown MJL4281A and MJL4302A output transistors, these have been available for over 6 years and are still hard to get. The recommended alternatives are MJL21193 and MJL21194.
    Note: It is no longer possible to recommend any Toshiba devices, since they are the most commonly faked transistors of all. The 2SA1302 and 2SC3281 are now obsolete, and if you do find them, they are almost certainly counterfeit, since Toshiba has not made these devices since around 1999~2000.
    Before applying power, make sure that VR1 is set to maximum resistance to get minimum quiescent current. This is very important, as if set to minimum resistance, the quiescent current will be very high indeed (almost certainly enough to blow the output transistors!).
    Construction Since I have boards available for this amp, I obviously suggest that these be used, as it makes construction much easier, and ensures that the performance specifications will be met. Note that the layout of any power amplifier is quite critical, and great pains were taken to minimise problem areas - if you make your own PCB, it is unlikely that you will be able to match the published specifications.
    All resistors should be 1/4W or 1/2W 1% metal film for lowest noise, with the exception of R9, R10 and R15 which should be 1/2W types, and R13, R14 must be 5W wirewound.
    The bootstrap capacitor (C5) needs to be rated for at least 25V (preferably 35V), but the other electrolytics can be any voltage you have available. The trimpot (VR1) should ideally be a multiturn, but an ordinary single turn pot can be used. Setting the current will be a little more difficult with a single turn pot, and they are not as reliable.
    A pair of these amps will be quite happy with a 1°C/W heatsink for normal hi-fi use if the quiescent current is maintained at the minimum recommended of 20mA. For higher quiescent current or if you expect to push the amp, use a larger heatsink. Consider using a fan if you are going to push the amp hard. Remember - there is no such thing as a heatsink that is too big.
    Basic Specifications The following shows the basic measurement results ...


    Gain27dB Input Impedance24k Input Sensitivity1.22V for 100W (8 ohms) Frequency response 110Hz to 30kHz (-1dB) typical Distortion (THD)0.04% typical at 1W to 80W Power (42V supplies, 8 ohm load) 290W Power (35V supplies, 8 ohm load) 360W Power (35V supplies, 4 ohm load)100W Hum and Noise 4-73 dBV unweighted DC Offset< 100mV Notes

    1. The frequency response is dependent on the value for the input and feedback capacitors, and the above is typical of that when the specified values are used. The high frequency response is fixed by C4, and this should not be changed.
    2. Operation into 4 ohm loads is not recommended with the 42V supplies. Peak dissipation will exceed 110W in each output transistor, leaving no safety margin with typical inductive loads. All supply voltages are nominal, at no load - your transformer may not be capable of maintaining regulation, so power may be slightly less than shown.
    3. This figure is typical, and is dependent on the regulation of the power supply (as are 1 and 2, above). Worst case power with 8 ohm loads is about 50W, but the supply will be seriously inadequate if the power falls that far.
    4. This is an extremely pessimistic test, because the bandwidth extends well above and below anything that is audible. The response of my meter extends from around 3Hz to well over 100kHz, so the measured noise is much greater than would be the case with any weighting network.

    Four of these amps in a biamped arrangement will give you prodigious SPL, and is similar to the arrangement I am using. Coupled with a Linkwitz-Riley crossover, the amplifiers can be mounted in the back of the speaker box, so only signal and power are needed for a complete system that will leave most commercial offerings for dead.
    Powering Up If you do not have a dual output bench power supply - Before power is first applied, temporarily install 22 Ohm 5 W wirewound "safety" resistors in place of the fuses. Do not connect the load at this time! When power is applied, check that the DC voltage at the output is less than 1V, and measure each supply rail. They may be slightly different, but both should be no less than about 20V. If widely different from the above, check all transistors for heating - if any device is hot, turn off the power immediately, then correct the mistake.
    If you do have a suitable bench supply - This is much easier! Slowly advance the voltage until you have about ±20V, watching the supply current. If current suddenly starts to climb rapidly, and voltage stops increasing then something is wrong, otherwise, continue with testing. (Note: as the supply voltage is increased, the output voltage will decrease - down to about 2V, then quickly drop to near 0V. This is normal.)
    Once all appears to be well, connect a speaker load and signal source (still with the safety resistors installed), and check that suitable noises (such as music or tone) issue forth - keep the volume low, or the amp will distort badly with the resistors still there if you try to get too much power out of it.
    If the amp has passed these tests, remove the safety resistors and re-install the fuses. Disconnect the speaker load, and turn the amp back on. Verify that the DC voltage at the speaker terminal does not exceed 100mV, and perform another "heat test" on all transistors and resistors.
    When you are satisfied that all is well, set the bias current. Connect a multimeter between the collectors of Q7 and Q8 - you are measuring the voltage drop across the two 0.33 ohm resistors. The most desirable quiescent current is 75mA, so the voltage you measure across the resistors should be set to 50mV ±5mV. The setting is not overly critical, but at lower currents, there is less dissipation in the output transistors. Current is approximately 1.5mA / mV, so 50mV will represent 75mA quiescent current.
    After the current is set, allow the amp to warm up (which it will), and readjust the bias when the temperature stabilises. This may need to be re-checked a couple of times, as the temperature and quiescent current are slightly interdependent. When you are happy with the bias setting, seal the trimpot with a dab of nail polish.

    If the temperature continues to increase, the heatsink is too small. This condition will (not might - will) lead to the destruction of the amp. Remove power, and get a bigger heatsink before continuing. Note also that although the power transistors are mounted to the board, never operate the amp without a heatsink - even for testing, even for a short period. The output transistors will overheat and will be damaged. When all tests are complete, turn off the power, and re-connect speaker and music source.
    Power Supply Before describing a power supply, I must issue this ...


    WARNING: Mains wiring must be done using mains rated cable, which should be separated from all DC and signal wiring. All mains connections must be protected using heatshrink tubing to prevent accidental contact. Mains wiring must be performed by a qualified electrician - Do not attempt the power supply unless suitably qualified. Faulty or incorrect mains wiring may result in death or serious injury. A simple supply using a 25-0-25 transformer will give a peak power of about 75W into 8 ohms, or 60W or so continuous. This is influenced by a great many things, such as the regulation of the transformer, amount of capacitance, etc. For a pair of amps, a 300VA transformer will be enough. Feel free to increase the capacitance, but anything above 10,000uF brings the law of diminishing returns down upon you. The performance gain is simply not worth the extra investment.

    Figure 2 - Recommended Power Supply For the standard power supply as noted above I suggest a 300VA transformer. In 230/240V countries, use a 3A fuse or the value suggested by the transformer manufacturer. For 115V countries, the fuse should either be 6A or as advised by the manufacturer, and in all cases a slow blow fuse is required because of the inrush current of the transformer and capacitors.
    The supply voltage can be expected to be higher than that quoted at no load, and less at full load. This is entirely normal, and is due to the regulation of the transformer. In most cases, it will not be possible to obtain the rated power if the transformer is not adequately rated.
    The bridge rectifier should be a 35A type, and filter capacitors must be rated at a minimum of 50V. Wiring needs to be heavy gauge, and the DC must be taken from the capacitors - not from the bridge rectifier.

  12. #29
    مدیر انجمن javad naderi آواتار ها
    تاریخ عضویت
    Jan 2011
    نام
    جواد نادری زاده
    نوشته ها
    830
    تشکر
    225
    تشکر شده 1,334 بار در 602 پست

    پیش فرض

    Circuit Description There are many instances where a simple and reliable power amplifier is needed - rear and centre channel speakers for surround-sound, beefing up the PC speakers, etc.
    This project (unlike most of the others) is based almost directly on the "typical application" circuit in the National Semiconductor specification sheet. As it turns out, the typical application circuit is not bad - would I go so far as to say hi-fi in the audiophile sense? Perhaps - with caveats. It has good noise and distortion figures, and is remarkably simple to build if you have the PCB.
    26 Sept 2000
    From testing the prototype boards, I was a little more critical of everything. The sound quality is excellent! As long as the protection circuitry is never allowed to operate, the performance is exemplary in all respects.
    The latest version of the ESP P19 board (Rev-B) has deleted the connections for a SIM (Sound Impairment Monitor). Much as I like the idea, no-one else seemed to be interested, so the small amount of PCB real estate thus liberated was used to refine the layout and provide space for input (and power) connectors.
    Figure 1 shows the original schematic as shown when this project was originally published. It is almost the same as in the application note (redrawn), polyester bypass capacitors have been added, and the mute circuit has been disabled (this function would more commonly be applied in the preamp, and is not particularly useful anyway IMHO).

    Figure 1 - LM3876T Power Amplifier Circuit Diagram (Original Version) Voltage gain is 27dB as shown, but this can be changed by using a different value resistor for the feedback path (R3, currently 22k, between pins 3 and 9). The inductor consists of 10 turns of 0.4mm enamelled copper wire, wound around the body of the 10 Ohm resistor. The insulation must be scraped off each end and the wire is soldered to the ends of the resistor.
    The 10 Ohm and 2.7 Ohm resistors must be 1 Watt types, and all others should be 1% metal film (as I always recommend). All electrolytic capacitors should be rated at 50V if at all possible, and the 100nF (0.1uF) caps for the supplies should be as close as possible to the IC to prevent oscillation.
    The supply voltage should be about +/- 35 Volts at full load, which will let this little guy provide a maximum of 56 Watts (rated minimum output at 25 degrees C). To enable maximum power, it is important to get the lowest possible case to heatsink thermal resistance. This will be achieved by mounting with no insulating mica washer, but be warned that the heatsink will be at the -ve supply voltage and will have to be insulated from the chassis. For more info on reducing thermal resistance, read the article on the design of heatsinks - the same principles can be applied to ICs - even running in parallel. I haven't tried it with this unit, but it is possible by using a low resistance in series with the outputs to balance the load.

    Figure 2 - Revision-B Power Amplifier Circuit Diagram The schematic for Revision-B boards is shown above. It is almost identical, except the SIM connections have been deleted and a few component designations have been moved around. Like the original, there is excellent on-board decoupling, using a 220uF electrolytic and a 100nF polyester or monolithic ceramic capacitor on each rail. While I have shown C1 as a 3.3uF bipolar electro, you can use a polyester cap if you desire. If the amp is to be used for midrange or tweeter in a biamped or triamped system, C1 may be reduced in value to 100nF (-3dB at 72Hz). For general use, you can use a 1uF polyester, giving a -3dB frequency of 7.2Hz, however bass extension will be better with a higher value as shown.
    The new PCB allows you to operate the amp as dual mono - the PCB track can be split, and each amp is powered from its own supply. While IMO there isn't much point, this also allows the PCB to be cut in half, and each half has its own supply connector. Output connection can be made to PCB pins, or you can use a PCB mount 'spade' (aka quick-connect) lug - the board has provision for this.
    Full construction details are available when you purchase the PCBs, and all options are explained in detail.
    As you can see, there is provision to use the LM3886 as well. This IC is almost identical, but has a higher specification. There are links on the PCB to connect pins 1 and 5 (these should not be connected for the LM3876). Using the LM3886, the board can be operated in bridge (BTL or bridge tied load) to obtain around 120W into 8 ohms. I suggest that the P87B be used to provide the out-of-phase signals needed for BTL operation. While it is common to run one amp as inverting, this presents a very low impedance to the preamp, and may cause unacceptable loading and possibly distortion. The P87B will drive each amplifier separately, and is the better way to drive the amplifiers.
    While parallel operation is often recommended, I absolutely do not recommend that you run the amps in parallel. There are very strict requirements for gain tolerance for parallel operation - typically the amplifiers should be matched to within 0.1% or better over the entire audio bandwidth and beyond. Because of the very low output impedance of the ICs, even a mismatch of 100mV (instantaneous, at any voltage or frequency) will cause large circulating currents through the ICs. While 0.1Ω resistors are usually suggested, a 100mV voltage mismatch (0.15% at a peak voltage of 60V) will cause a circulating current of 0.5A. This causes overheating and will invoke the wrath of the protection circuits.

    Figure 2 - IC Pinouts Figure 2 shows the pinouts for the LM3876, and it should be noted that the pins on this device are staggered to allow adequate sized PCB tracks to be run to the IC pins. The 3886 has (almost) identical pinouts, and can be used instead if a little more power is required. The only difference in pinouts is that pin 5 must be connected to the +ve supply for the LM3886. Provision for this link is on the PCB.
    The PCB for this amp is for a stereo amplifier, is single sided, and supply fuses are located on the PCB. The entire stereo board including four fuses is 115mm x 40mm (i.e. really small). The Revision-B board is exactly the same size, and uses the same spacing between ICs to allow retro-fitting if necessary.

    Photo of Completed Amplifier (With Heatsink) To reiterate a point I have made elsewhere, never operate this amp without a heatsink - even for testing (this applies to nearly all amplifiers). It will overheat very quickly, and although the internal protection will shut the amp down to protect it from damage, this is not something you want to test for no good reason.
    How Does It Sound? The sound quality is very good - as I said at the beginning, I would call it audiophile hi-fi - with caveats. Provided the amp is never allowed to go anywhere near the protection limits it sounds very good indeed. This is the rub - because of the comprehensive overload protection (which I have never liked in any form) this amp provides more and nastier artefacts as it clips than a "normal" amplifier. With the recommended ±35V supplies and a nominal 8 ohm load, you will need a good heatsink to ensure that device temperature is kept below 70°C. This will usually ensure that the protection circuits don't operate even if the amp clips on transients. For 4 ohm loads, I suggest that the supply voltage be reduced to a maximum of about ±30V.
    The protection circuitry is called SPiKe™ by National - this stands for Self Peak instantaneous Temperature (°Ke) (sic) and will protect the amp from almost anything. Although in theory this is a good thing, it's not so good when the protection circuits operate, so make absolutely sure that the amp is only used in applications where clipping will never occur, or is relatively lightly loaded.
    This might sound like a tall order, but for rear speakers in a surround system, or to put some serious grunt into those 400W PMPO PC speakers (with the 5W RMS amplifiers - I'm not kidding), this amp is a gem.
    It could also be used as a midrange and/or tweeter amp in a tri-amped system - there are a lot of possibilities, so I will leave it to you to come up with more.

  13. #30
    مدیر انجمن javad naderi آواتار ها
    تاریخ عضویت
    Jan 2011
    نام
    جواد نادری زاده
    نوشته ها
    830
    تشکر
    225
    تشکر شده 1,334 بار در 602 پست

    پیش فرض

    Introduction I have been trying for years to find high quality solution for power audio amplifier. I have tried valves (tubes), bipolar transistors, MOSFETs, Class-B, AB, A push-pull, A single-ended ... you know what stuff I speak about.
    Nelson Pass describes those terms perfectly (see www.passlabs.com). He also describes why he prefers the solution of single-ended class A MOSFET power stage with common Source (S-electrode). I think that his thoughts can be broadened even more. From my point of view a power MOSFET follower is a still better solution. It has benefits of single-ended class A amplifiers with common Source plus something more - less distortion, lower output impedance, higher input resistance and ... no feedback.
    With one drawback - voltage gain is only +1 **, so it needs preamplifier able to deliver up to 12V RMS. The sound impression is perfect, surpassing the common Source MOSFET circuit. You can see schematic that I have tested in Fig.1.
    ** The actual voltage gain is in fact 0.98 (for RL=8 Ohm), as the IRF350 MOSFET transconductance is 6 [1/Ohm] and therefore ...
    Gain = 6 / (6 + 1 / 8) = 0.979
    Measurement gave the same number.
    Description The circuit consists of an N-Channel MOSFET voltage follower T1 (common Drain) and current source T2 (NPN Darlington). Current source is set to 2.2 Amps. With 40V of supply voltage the circuit is able to deliver about 17W into an 8 Ohm loudspeaker. The amplifier will take 88W from the power supply all the time.

    Figure 1 - MOSFET Power Follower
    Bandwidth (-3dB) is from 4Hz to 250kHz. Rise time is 1.5 us. Output resistance 0.16 Ohm. The circuit is very tolerant of different kinds of load. Input resistance is 10 kOhm (R0), but can be increased up to 100 kOhm (R4) by omitting R0. Input capacitance remains relatively high, about 1500 pF. For this reason, the preamp should not have higher output impedance than 1 kOhm to maintain high frequency limit about 100 kHz. An input potentiometer can be used instead of R0.
    The drawings shown are slightly different from Pavel's original. A fixed resistor has been used for the zener feed, and I made a couple of minor changes so the schematic was more like my standard style.
    If the value of the potentiometer is 5 k Ohm then the high frequency limit will be about 70 kHz. The power follower can be connected directly to the output of CD player, and for reduction of volume potentiometer 5 kOhm can be used. As a preamplifier you may use Nelson Pass's projects "Bride of Zen" or "Balanced Line Stage" (see passlabs.com).
    Note: The DoZ preamp will also drive this amplifier well, especially if the supply voltage is increased slightly. Although it is specified for +30V, it will operate quite happily at up to +40V. It may also be possible to direct couple the preamp's output to the power follower - omit R0, R2, R3, R4, C1 and C2 - as well as the output capacitor on the preamp. Needless to say, this would be my recommendation as the ideal preamp for Pavel's circuit - especially with direct coupling (see below). There are some changes needed to use the latest revision of the DoZ preamp, because it uses dual power supplies. More info below.
    How does it sound? Wonderful, regardless low or high volume. Entire spectrum from bass to high is perfect. It only needs a good preamplifier.
    I have tested an amp for a considerable amount of time and there was never problem with thermal runaway. Normally, the thermal coefficient of zener voltage of 3V type is negative, and so is Ube voltage of the Darlington transistor. As Ube is reduced by -2mV/°C, zener voltage also goes down with increasing temperature inside a box (but the zener is not on the heat sink of the MOSFET and should not be). In fact there was a fluctuation of 40mA at 2A constant current, from my point of view it is negligible. Of course the heatsink for T1 and T2 should be better than 0.5°C/W for each transistor, so four such heatsinks are needed for stereo.
    PROS:

    • simplicity, easy as a DIY project (Do It Yourself)
    • low distortion
    • no feedback
    • lower output impedance compared to common Source circuit
    • higher input resistance compared to common Source circuit
    • crossover distortion eliminated
    • wide bandwidth
    • fast response
    • no overshoot, no ringing

    CONS:
    • voltage gain is only +1
    • runs pretty hot, so needs a very good heatsink
    • high input capacitance of power MOSFET (about 1500pF)
    • because of high input capacitance the preamplifier must have output impedance no higher than 1kOhm

    KD367B! - very funny thing. I am from Prague, Czech Republic. The KD367B is a product of the former TESLA of Czechoslovakia, now they are a part of Motorola and are not produced any more ... TIP141 or TIP142 will do the same work without any problem.
    KD367B's parameters:
    NPN Darlington
    Ucbo <= 100V
    Uceo <= 100V
    Ic <= 8A
    Ib <= 0.15A
    Ptot <= 60W
    hFE = 1000 approx.
    Rthjc <= 2.1°C/W
    fT = 7MHz
    TO3 case
    Comments: macura@centrum.cz
    Using the DoZ Preamp as a Driver To get the voltage gain needed for a normal installation, the DoZ preamp can be used. Everyone who has built this circuit has commented on the exceptional sound quality, and it is ideally suited to this application. Pavel has tried the combination, and he says ...
    I have already checked the DoZ with the Follower. Both original versions, with caps (not direct coupled). The DoZ being supplied from external 30V power supply. The DoZ and the Follower interconnected by 5 kOhm potentiometer. Works perfectly, sounds wonderful.

    Figure 2 - DoZ Preamp as Driver
    Figure 2 shows the modified version of the preamp, the output of which would be connected directly to R1 in Pavel's circuit. The quiescent output voltage is now set by VR1 in the preamp, and the voltage at the source of T1 should be set to 19.8V as shown in Figure 1 by means of VR1 - the voltage at the gate (preamp output) should be 4V higher, i.e. 23.8V. The DoZ preamp board is stereo, and can drive a pair of Pavel's power followers with ease. Q2 and Q3 should be fitted with small "flag" heatsinks to allow them to dissipate the increased power caused by the higher operating voltage. Note that the current version of the DoZ preamp is normally operated from a split supply (positive and negative supply rails), but it is reasonably easy to modify it as shown above. I will provide full modification details if there is sufficient interest.
    As shown, the gain is 3.2, so it will require nearly 4V RMS input for full power. To change the gain, I suggest that R5 be changed to 3k3 to obtain a gain of 7.7 (17.7dB), which will give an input sensitivity of about 1.5V for maximum output. C3 will also need to be changed, and a value of 100uF will be more than adequate. I do not recommend that R4 be reduced to less than 2k7, which will give a gain of 9.15 (19.2dB). To maintain good low frequency response, C2 will need to be about 100uF, although even with 25uF, the low frequency response is maintained to 2Hz. Ideally, the input network should define the low frequency limit, so the higher value is recommended if R5 is reduced. The capacitor marked C* does not normally exist on the PCB, so needs to be added.
    Unless a preamp is used in front of the amp, a pot will be needed at the input for gain control. 10k is fine here, and will not cause excessive loading on the source.
    Figure 3 shows what Pavel's amplifier looks like after it is modified for direct coupling to the DoZ preamp. The complete circuit is deceptively simple, but should give a very good account of itself.

    Figure 3 - Power Follower Modified for Direct Coupling
    The amplifier can also be used to drive headphones, and the quiescent current may be reduced considerably. R6 controls the current, and may be increased to 10 Ohms for use as a headphone amp. This will reduce the current to about 200mA and dramatically reduces the heatsinking requirements. 120 Ohm resistors should be used in series with the headphone output, and C3 can be reduced to 220uF for a single headphone output, or 470uF for dual outputs (using 2 x 120 ohm resistors). Smaller (and cheaper) MOSFETs can be used at the lower power, but they need to be carefully selected to ensure that there is no oscillation (continuous or parasitic).

    Figure 4 - Direct Coupled Power Follower Using MOSFET Current Source
    A further modification that a reader (thanks Shaan) has tried and tested is shown above. Using IRFP150N MOSFETs as both the amplifier and current source, the problem of finding a suitable Darlington transistor goes away. While the lower MOSFET increases the available voltage swing by a couple of volts, this doesn't make it sound any different or produce any audible power increase. R6 may be a single 0.33 ohm resistor, or 3 x 1 ohm resistors in parallel. Total dissipation of R6 is 1.6W, so 3 x 1W resistors will work fine. Non-inductive resistors are highly recommended to prevent any possibility of RF oscillation. It may be necessary to reduce the value of R6 to obtain the specified 2.2A quiescent current. Any reduction of resistance will be small - the theoretical resistance for 2.2A is 0.295Ω
    The specified IRFP150N MOSFETs are rated at 160W, and use the TO-247 package so heat transfer to the heatsink is better than average (although not as good as the TO-3 package). It is also a good substitute for the original IRF350, which is very expensive and/or difficult to obtain now. There are differences as one would expect, but these are unlikely to make a great deal of difference to the measured or audible performance.
    Note: Do not attempt to use any TO-220 packaged MOSFET regardless of claimed performance, because heat transfer is not good enough for continuous operation at these power levels (about 44W for each device). The TO-220 package should not be expected to handle more than about 20W continuous power.
    While you would expect that a gate "stopper" resistor would be needed for the lower MOSFET, Shaan tells me that it caused the current source to oscillate. Once removed the circuit behaved itself perfectly and there is no signal degradation cause by the use of the MOSFET. Note that I have not tested this variation, but I expect that it will work without any problems.
    Pavel has also sent me his version of the power follower using discrete transistors as the current source. Rather than the Darlington transistor, it uses an MJE15030 driver and MJL21194 power transistor. An extra resistor has been added in series with the gate, as this was found to be necessary under some conditions and with some wiring layouts.

    Figure 5 - Pavel's Latest Version Direct Coupled Power Follower
    Pavel quotes distortion figures of 0.065% THD at 400mW, rising to 0.43% at 10W output. From a regulated 37.5V supply, you can expect about 30V peak-to-peak into a 10 ohm load (about 11W), or 20V p-p into 5 ohms (10W).
    Note that Pavel specifies an 18V zener diode for gate protection, but I suggest either 12V or 15V. There is no conceivable audio signal that can ever reach more than about 6V between the gate and source, and allowing a higher maximum voltage will not improve performance. It will allow extremely high current to flow though, so there is no disadvantage in lowering the zener voltage.

  14. #31
    مدیر انجمن javad naderi آواتار ها
    تاریخ عضویت
    Jan 2011
    نام
    جواد نادری زاده
    نوشته ها
    830
    تشکر
    225
    تشکر شده 1,334 بار در 602 پست

    پیش فرض

    Introduction As readers will know, there are already several power amplifier projects, two using IC power amps (aka power opamps). Both have been popular, and this project is not designed to replace either of them. However, it is significantly smaller than the others, so it makes building a multiple amp unit somewhat easier because the space demand is much lower. It's quite simple to include 4 amps (two boards) into a small space, but be aware that good heatsinking is essential if you expect to run these amps at significant power levels.

    Photo of Completed P127 Board The TDA7293 IC uses a MOSFET power stage, where the others featured use bipolar transistors. The main benefit of the MOSFET stage is that it doesn't need such radical protection circuitry as a bipolar stage, so unpleasant protection circuit artefacts are eliminated. There are no apparent downsides to the TDA7293, although it was found that one batch required a much higher voltage on the Standby and Mute pins than specified, or the amps would not work. This is not a limitation, since both are tied to the positive supply rail and are therefore disabled.
    This particular project has been planned for a long time, but for some reason I never got around to completing the board or the project description. This is now rectified, and it's ready to "rock and roll". The board is very small - only 77 x 31mm, so getting it into tight spaces is easy ... provided adequate heatsinking is available of course.
    Description The TDA7293 has a bewildering number of options, even allowing you to add a second power stage (in another IC) in parallel with the main one. This improves power into low impedance loads, but is a rather expensive way to get a relatively small power increase. It also features muting and standby functions, although I've elected not to use these.
    The schematic is shown in Figure 1, and is based on the PCB version. All unnecessary functions have been disabled, so it functions as a perfectly normal power amplifier. While the board is designed to take two TDA7293 ICs, it can naturally be operated with only one, and the PCB is small enough so that this is not an inconvenience. A LED is included to indicate that power is available, and because of the low current this will typically be a high brightness type.

    Figure 1 - Schematic of Power Amplifier (One Channel Shown) The IC has been shown in the same format that's shown in the data sheet, but has been cleaned up for publication here. Since there are two amps on the board, there are two of most of the things shown, other than the power supply bypass caps and LED "Power Good" indicator. These ICs are extremely reliable (as are most power amp ICs), and to reduce the PCB size as much as possible, fuse clips and fuses have not been included. Instead, there are fusible tracks on the board that will fail if there is a catastrophic fault. While this is not an extremely reliable fuse, the purpose is to prevent power transformer failure, not to protect the amplifiers or PCB.
    I normally use a gain of 23 (27dB) for all amplifiers, and the TDA7293 is specified for a minimum gain of 26dB, below which it may oscillate. Although this is only a small margin, tests so far indicate that the amp is completely stable. If you wish, you may increase the gain to 28 (29dB) to give a bit more safety margin. To do this, just change the input and feedback resistors (R3A/B and R4A/B) from 22k to 27k.
    The circuit is conventional, and is very simple because all additional internal functions are unused. The LED is optional, and if you don't think you'll need it, it may be omitted, along with series resistor R3. All connections can be made with plugs and sockets, or hard wired. In most cases, I expect that hard wiring will be the most common, as the connectors are a pain to wire, and add unnecessary cost as well as reduce reliability.
    The TDA7293 specifications might lead you to believe that it can use supply voltages of up to ±50V. With zero input signal (and therefore no output) it might, but I don't recommend anything greater than ±35V if 4 ohm loads are expected, although ±42V will be fine if you can provide good heatsinking. In general, the lower supply voltage is more than acceptable for 99% of all applications, and higher voltages should not be used unless there is no choice. Naturally, if you can afford to lose a few ICs to experiments, then go for the 42V supplies (obtained from a 30+30V transformer).
    This amp can also be bridged, using the Project 87 balanced transmitter board. You can expect about 150W into 8 ohms from a +/-35V supply. It cannot be bridged into 4 ohms, as the effective impedance on each amplifier is too low.
    Construction Because of the pin spacings, these ICs are extremely awkward to use without a PCB. Consequently, I recommend that you use the ESP board because it makes building the amplifier very simple. The PCBs are double sided with plated-through holes, so are very unforgiving of mistakes unless you have a good solder sucker. The best way to remove parts from a double sided board is to cut the pins off the component, then remove each pin fragment individually. This is obviously not something you'd wish to do if a power amp IC were installed incorrectly, since it will be unusable afterwards.

    Figure 2 - TDA7293V Pinouts The diagram above shows the pinouts for the TDA7293V (the "V" means vertical mounting). Soldering the ICs must be left until last. Mount the ICs on your heatsink temporarily, and slide the PCB over the pins. Make sure that all pins go through their holes, and that there is no strain on the ICs that may try to left the edge off the heatsink. When ICs and PCB are straight and aligned, carefully solder at least 4 pins on each IC to hold them in place. The remaining pins can then be soldered. Remember, if you mess up the alignment at this point in construction, it can be extremely difficult to fix, so take your time to ensure there are no mistakes.
    This amplifier must not be connected to a preamp that does not have an output coupling capacitor. Even though there is a cap in the feedback circuit, it can still pass DC because there is no input cap on the PCB. I normally include an input cap, but the goal of this board was to allow it to fit into the smallest space possible, and the available board space is not enough to include another capacitor. A volume control (typically 10k log/ audio taper) may be connected in the input circuit if desired.
    Note that the metal tab of the TDA7293 is connected to the -Ve supply, so must be insulated from the heatsink. The more care you take with the mounting arrangement, the better. While you can use a screw through an insulating bush and a piece of mica to insulate the tab, a better alternative is to use a clamping bar of some kind. How you go about this depends a lot on your home workshop tools and abilities, but one arrangement I've found highly satisfactory is a suitable length of 6.25mm square solid steel bar. This is very strong, and allows good pressure on the mica (or Kapton) for maximum heat transfer. Naturally, heatsink compound is absolutely essential.
    Do not be tempted to use silicone insulation washers unless you are using the amp at very low supply voltages (no more than ±25V). Its thermal transfer characteristics are not good enough to allow the amp to produce more than about 10 - 20W of music, and even that can be taxing for silicone washers. The amp will shut down if it overheats, but that curtails one's listening enjoyment until it cools down again.
    Power Supply A suitable power supply is shown below, and is completely unremarkable in all respects. The transformer may be a conventional (E-I) laminated type or a toroid. The latter has the advantage of lower leakage flux, so will tend to inject less noise into the chassis and wiring. Conventional transformers are usually perfectly alright though, provided you take care with the mounting location.
    WARNING: This power supply circuit requires experience with mains wiring. Do not attempt construction unless experienced, capable and suitably qualified if this is a requirement where you live. Death or serious injury may result from incorrect wiring. The bridge rectifier should be a 35A 400V type, as they are cheap, readily available and extremely rugged. Electrolytic capacitors should be rated at 50V. The cap connected across the transformer secondary (C4) should be rated at 275V AC (X Class), although a 630V DC cap will also work. This capacitor reduces "conducted emissions", namely the switching transients created by the diodes that are coupled through the transformer onto the mains supply. The power supply will work without this cap, and will most likely pass CE and C-Tick tests as well, but for the small added cost you have a bit of extra peace of mind as regards mains noise.

    Figure 3 - Suggested Power Supply The supply shown includes a "loop breaker", which is intended to prevent earth/ ground loops to prevent hum when systems are interconnected. Please be aware that it may not be legal to install this circuit in some countries. The diodes must be high current types - preferably rated at no less than 3A (1N5401 or similar). The loop breaker works by allowing you to have the chassis earthed as required in most countries, but lets the internal electronics "float", isolated from the mains earth by the 10 ohm resistor. RF noise is bypassed by the 100nF cap, and if a primary to secondary fault develops in the transformer, the fault current will be bypassed to earth via the diodes. If the fault persists and the internal fuse (or main power circuit breaker) hasn't opened, one or both diodes will fail. Semiconductor devices fail short-circuit, so fault current is connected directly to safety earth.
    Be very careful when first applying mains power to the supply. Check all wiring thoroughly, verify that all mains connections are protected from accidental contact. If available, use a Variac, otherwise use a standard 100W incandescent lamp in series with the mains. This will limit the current to a safe value if there is a major fault.
    When the loop breaker is used, all input and output connectors must be insulated from the chassis, or the loop breaker is bypassed and will do nothing useful. The body of a level pot (if used) can be connected to chassis, because the pot internals are insulated from the body, mounting thread and shaft.
    Note that the DC ground for the amplifiers must come from the physical centre tap between the two filter caps. This should be a very solid connection (heavy gauge wire or a copper plate), with the transformer centre tap connected to one side, and the amplifier earth connections from the other. DC must be taken from the capacitors - never from the bridge rectifier.
    The order of the fuse and power switch is arbitrary - they can be in any order, and in many cases the order is determined by the physical wiring of the IEC connector if a fused type is used. With a fused IEC connector, the fuse is before the switch and it cannot be removed while the mains lead is inserted.

    I have shown a 2A slow-blow fuse, but this depends on the size and type of transformer and your mains supply voltage. Some manufacturers give a recommended fuse rating, others don't. The fuse shown is suitable for a 150VA transformer at 230V AC, and is deliberately oversized to ensure that it will not be subject to nuisance blowing due to transformer inrush current. A 2A fuse will fail almost instantly if there is a major fault.
    Make sure that the mains earth (ground) is securely connected to guarantee a low resistance connection that cannot loosen or come free under any circumstances. The accepted method varies from one country to the next, and the earth connection must be made to the standards that apply in your country.
    Testing Never attempt to operate the amplifier without the TDA7293 ICs attached to a heatsink!
    Connect to a suitable power supply - remember that the supply earth (ground) must be connected! When powering up for the first time, use 100 ohm 5W "safety" resistors in series with each supply to limit the current if you have made a mistake in the wiring. If available, use a variable bench supply - you don't need much current to test operation, and around 500mA is more than enough. If using a current limited bench supply, the safety resistors can be omitted. Do not connect a speaker to the amplifier at this stage!
    If using a normal power supply for the amp tests, apply power (±35V via the safety resistors) and verify that the current is no more than 60mA or so - about 6V across each 100 ohm resistor. No load current can vary, so don't panic if you measure a little more or less. Verify that the DC voltage at both outputs is less than 100mV. Using another 100 ohm resistor in series with a small speaker, or an oscilloscope, apply a sinewave signal at about 400Hz to the input and watch (or listen) for signal. The signal level needs to be adjusted to ensure the amp isn't clipping, and the waveform should be clean, with no evidence of parasitic oscillation or audible distortion.
    If everything tests out as described, wire the amplifier directly to the power supply and finish off any internal wiring in the amp. Once complete, it's ready to use.

  15. #32
    کاربر فعال nima_zeus آواتار ها
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    Amplificador cuasicomplementario de 50W por canal
    Este amplificador
    Este amplificador no solo es de potencia aceptable si no muy sencillo, por lo cual se recomienda
    para las personas que quieren aprender y entender el transistor.
    Esta configuración se conoce como amplificador clase AB cuasi complementario con par Darlington,
    e incorpora un par Darlington con transistores NPN y un par retro alimentado consistente en un
    transistor NPN y uno PNP.
    Los transistores de salida son NPN similares capaces de manejar alta potencia. Los transistores D400
    y A683 son complementarios y no necesitan manejar alta potencia
    فايل هاي پيوست شده فايل هاي پيوست شده

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  17. #33
    مدیر انجمن javad naderi آواتار ها
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    آمپلیفایر 200w با stk 4050 ساختم.اگر کسی خاست سفارش بده.

  18. #34
    مدیر انجمن javad naderi آواتار ها
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    سلام این آمپ رو تازه طراحی کردم 500 وات استریو با 8 ترنزیستور قدرت ماسفت.
    اگه کسی خواست سفارش بده برام پیغام بزاره.


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  20. #35
    کاربر دائمی alghasi آواتار ها
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    سلام به همه
    خيلي خوبه اما همه اين آمپلي فاير ها خطي هستند كه اتلاف توانشون خيلي بالاست. من مشغول ساخت و يه آمپلي فاير كلاس D با قدرت 1kw هستم. از دستان كي مايله به همكاري؟

  21. #36
    مدیر انجمن javad naderi آواتار ها
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    سلام آمپ 1کیلو وات تغذیه بالای 1300 وات میخواد تا بتونی توان نرمالشو بگیری یه چیزی حدود 150 تومن فقط ترانسشه خازن صافی هاشم بالای 100 تومن میشه تازه اینا هیچ هزینه بلندگوهاش سر به فلک میکشه.فکر اینارو کردی؟

  22. #37
    کاربر علاقه مند
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    نقل قول نوشته اصلی توسط alghasi نمایش پست ها
    سلام به همه
    خيلي خوبه اما همه اين آمپلي فاير ها خطي هستند كه اتلاف توانشون خيلي بالاست. من مشغول ساخت و يه آمپلي فاير كلاس d با قدرت 1kw هستم. از دستان كي مايله به همكاري؟
    من چندتا با توانای مختلف و روشهای مختلف ساختم اگه کمکی از دستم بر بیاد در خدمتم

  23. #38
    کاربر دائمی alghasi آواتار ها
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    نقل قول نوشته اصلی توسط me28k نمایش پست ها
    من چندتا با توانای مختلف و روشهای مختلف ساختم اگه کمکی از دستم بر بیاد در خدمتم
    من ديروز يه amp‌كلاس e ساختم. خيلي كوچيك و كم تلفات بود. اما توانش به 10w نرسيد.
    كلاس e براي تك تون سينوسيه. مجبورم برگردم به كلاس d.
    شما كلاس d ساختين؟ چه تواني رسيدين ؟ طبقه آخر رو چي گزاشتين و فركانس pwm چند بود؟

  24. #39
    کاربر دائمی alghasi آواتار ها
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    ببخشين غلط(قلت) املايي زياد دارم.

  25. #40
    کاربر علاقه مند
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    دوست عزیز من تا توان 2300 وات رسیدم فرکانسم در این آمپلیفایر 250 کیلوهرتز بود.

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