50 W transistor amplifier

Description. 

A very rugged and reasonably power amplifier circuit that can be used  for any audio applications. The amplifier produces 60W rms at 50V supply  on a 8 Ohm load.The circuit is designed such that most of the components are not critical and can be easily replaced by nearest values.This make it ideal to assemble from your electronics junk box.

 The capacitor C1 controls low frequencies and capacitor C2 controls high frequencies.The circuit ia basically a class B amplifier.The transistors 2N 3055  serves the function of driving the speaker.The other transistor functions  as pre amplifiers for the  driver stage.This is the basic scheme of the circuit.The maximum power level of amplifier can be  set by adjusting the 500 Ohm POT connected with the BC107 transistor.

 

Circuit diagram with Parts list.

 power-amp-50-w.jpg

Notes. 

  • The circuit can be powered using a 50 V DC power supply with 5A current rating.Up to 60 v can be given to the circuit.Any way the power supply must be well regulated and filters to avoid noise.
  • Adjust the 500 ohm POT  to obtain optimum performance.
  • All capacitors must be rated higher than the supply voltage.
  • Volume control can be attained  by connecting a 10 K POT in series to the input of the amplifier.(Not shown in circuit).

 

Show Comments

36 thoughts on “50 W transistor amplifier

  1. Christiaam

    HI sir i domt know what your name is but ive this circuit whouid like to know what is the RMS watts on this amplifier output

    Reply
  2. seetharaman

    TIP41/42 are good output transistors its gain may not be sufficient for driver application. You can try using them. you can use BD139/140 pair you can use BC327/337 8550/8050 CK100/CL100, 2N1711/ 2N1907 etc

    Reply
  3. seetharaman

    Hi Anish you require MIC preamplifier with a voltage gain of atleast 100. Because the mic output is around 2 to 3mV. for rated output the above amplifier requirement is around 300mV RMS. Why do you want to use a sledge hammer to hit a fly. you can use amplifier with 1 watt or 2watt capacity that is all what you require.

    Reply
  4. seetharaman

    Hi Jomots cannot be used as A733 is an NPN small gignal transistor. You can use BC558, BC158, 8550, BC327, BC328, 2N2907

    Reply
  5. SARATH

    I was trying to make fm 50 watt transmitter circuit.But i could not find the transistor BC286 .can you please help me what can i use insted of BC286

    Reply
  6. Seetharaman

    Hi Rupjyoti the problem is due to too much of HF response in modern silicon transistors. To avoid RF break through I always recommend a Low pass filter before main amplifier 1K in series with input signal and decoupled to ground with 470PF ceramic disc capacitor. The amplifier should be enclosed in metal chassis with common of the amplifier board connected to chassis at the input socket end. For reference see motional feedback amplifier appeared earlier.
    http://www.circuitstoday.com/motional-feed-back-amplifier

    Reply
  7. RUPJYOTI

    SEETHARAMAN SIR,
    I MADE THIS CIRCUT AND SOUND QUALITY IS GOOD BUT LOTS OF NOISE IS COMING WHEN NO INPUT IS GIVEN. WHEN I CONNECT A SOURCE AND MUTE IT SOME RADIO CHANNEL’S VOICE IS COMING, WHAT I DO SIR. (I USE 2.2K AND 22OHM IN THE EMITTER CIRCUIT OF BC212.I USE BC157 INSTEAD OF BC212,BD140 INSTEAD OF BC287, BD139 INSTEAD OF BC286).SORRY BAD ENGLISH

    Reply
  8. alandeaker

    Hello again
    I’m having troubles with this circuit, I can’t find the exact transistors. I’m think that is the problem.
    Could you give me a list with replaces?
    Thanks

    Reply
  9. gregtherider

    HElo!

    If I understand you right you want to know what are the power ratings for resistors?
    As far as I can remember the resistors around 2N3055 transistors have to be at about 5W all others can be 1/4W.

    Correct me if I am wrong.

    Reply
  10. Alandeaker

    Hello
    I have a question about this circuit. There are power resistances or what are the power capacity of all resistances?
    PD: Sorry by my bad english, je.
    Thanks and greetings from Ecuador.

    Reply
  11. seetharaman

    Hi Kapo both bc286s and bc287 requires small finned TO39 cooling clips. both the power trasistors require extruded aloy large heat sink sitable for TO3 casing.

    Reply
  12. Ezekiel Fernandez

    Thanks for the reply… i’ll try to seek out the problem…. anyway i think we had problems on the transistor replacements

    Reply
  13. seetharaman

    Hi Mr fernabdez you should get 25 to 30 volt at out put transistor emitter resistance junction conection to speaker coupling capacitor positive terminal. if not there is something wrong in the wiring. This circuit is based on philips audio application book 1972. a stable reliable amplifier.
    donot give up please find out the problem and solve it you will appreciate the results.

    Reply
    • admin Post author

      Reply to Ezekiel Fernandez

      There is no problem with this circuit.I think you may have made some connections wrong. Also,you need to adjust the 500 ohm POT for optimum performance.This circuit is successfully tested by many guys.

      Reply
  14. gregtherider

    Hi again. Problem solved. One of the BC transistors was fake. I replaced it and now amp is working fine and its fu**** loud!
    Thanks for that circuit!

    Reply
  15. gregtherider

    Hi! I built this amp and it`s not working. I triple checked everything and it looks ok to me. But when I connect it to power nothing happens. I measured the standby current(current to the circuit when not loaded) and its very low (4.5mA). Power supply is 35V 5A. I measured all transistors with multimeter and they seem ok.
    Does anyone have an idea what could be wrong?

    Reply
  16. chuan

    HI
    This chart uses pspice to simulate may ??
    ok or no
    And tells me All transistor’s function is??

    And tells me the oscillogram the illustration

    Thanks

    Reply
  17. seetharaman

    BC212 is for stailising half supply at positive end of spkr coupling capacitor. BC286 is driver, BC286/287 is a complimentry driver for output 2N3055. BC107 is the thermal compensation as well quisent current stabiliser for out put transistor 2N3055s (say around 50mA). The gain of the amplifier is governed by emitter resistance of BC212 2-3K and 20 to 100ohms resistance. you can adjust the ratio in such a way you maintain around a gain of 50, for better frequency response and distortion due to over loads. wish you happy listening.

    Reply
  18. seetharaman

    you can use european components like BC177/557/157B for BC212, medium power BD137/BD139 can be used for BC286, BD138/BD140 can be used for BC287 which are quite rugged and reliable. please note these plastic medium power transistors have center lead collector left emitter and right base as you view the leads and metal heat sink portion viewing down. this is a very reliable amplifier. Please enjoy the sound with solid punch and power.

    Reply
  19. Rezwan

    Hi, I was trying to build the circuit for 50 W transistor amplifier on Multisim but I couldn’t find transistor BC286 and BC287. Can you please tell me what can I use instead of them? Are there any equivalent transistors? Thank you in advance.

    Reply

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