This is the circuit diagram of a fully transistorized sub woofer amplifier that can produce an output of 100W.There are seven transistors including four in the output stage. The transistors Q1 and Q2 form the preamplifier stage. Transistors Q4 to Q7 form the output stage. Since no ICs are used the circuit is very robust and can be easily assembled on a general purpose PCB.

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Circuit diagram with Parts list.


  • The circuit can be powered from a +35V/-35V, 5A dual power supply.
  • Use a 100W, 12 inch sub woofer at the output.
  • All electrolytic capacitors must be rated 100V.
  • The transistor Q4 to Q7 must be fitted with heat sinks.


  1. dear seetharaman,
    the amplifier output is very low, Q5 standing current is 30ma, output dc is -0.16v, all the transistors are very max volume Q5 collector current remains 200ma . o/p is nearly 20 watts only . what’s the problem. anyone fix the solution

  2. i am looking if someone help me buy this circuit or help me from start as i am new to this kinda stuff and all the stuff is available in India or not? os do i have to buy it from abroad

  3. hey yar i m getting the out but its not clear… its notmuch louder and bass is also insufficeint ??

    wat should i do now ?

  4. superb can use any voltage in between 30-0-30 up to 60-0-60 .if you try to make it plzz use heavy heat sink for power transistors.use bridge rectifiers insted of diods. use .33 ohm resistor having 5w or more.if you wired it well the out put must be just enjoying this sub amp

  5. hii, i have designed this cct on the bread board yet …. but i m not getting accurate out put…. the output is a hum sound and low amplifiyng signal 🙁 wat should i do now ? plz help me seetharamen ……

  6. and i also want to know the pin layout of transistor 2N3773…. i will b very thankful to u seetheraman!!

  7. hi seetheraman, how r u? i have a question about the subwoofer low pass filter…. is it connected to the input of the subwoofer circuit or at the output?

  8. Seetharaman

    Hi Aris you can use ceramic or polyester capacitor for all except C17 which can be electrolytic or polyester as it is difficult to get in ceramic.
    HI Lordsville I can suggest a very simple cross over which is just sufficient Woofer through 300turns of 18SWG enameled copper wire (1mm dia wire will do)on 25mm dia plastic former wound for 40mm length. Mid range through 25uF non polar capacitor or 2nos 50uF electrolytic connected back to back and tweeter through 2.5uF non polar (here you can use a polyester or paper or 48″ ceiling fan run capacitor)or 2nos 5uF (4.7uF standard value) electrolytic capacitors connected back to back. I am using in my system an 8″ Philips 40Watts woofer, 6″ X 4″ Philips standard speaker as midrange and Philips 1″ Dome tweeter.

  9. lordsville

    Thx a lot SEETHE::I have recently upgraded the transformers to dual 25v ac. Abt 50v. And it drives my 12-inch Sony speakers like mad but there is a volume limit so I wont damage them.Im thinking of buying Two 10-inch 8-ohms heavy magnet subwoofer speakers with tweeters and midrange speakers,,all 8-ohms.. to build 2 loudspeakers.Is this configuration convinient and do i need u know abt the best kind of crossover circuit i can use.

    Thx a lot.

  10. Seetharaman

    Hi Aris you can use with sub woofer filter you have to increase input coupling capacitor to 2.2uF 50volt + terminal connected to Q1 Base. with 0.22uF low end cut off will be around 90Hz to still better low frequency response you have to increase the value of C1 to 2.2uF

  11. thanks for all the support sir! this project is really great, of course with your support! thanks a lot!

  12. hello sir seetheraman,
    i found my problem, it was Q3 and Q4 mounted on the same heatsink with their screws un-insulated, i removed the other one now it works fine!
    just as you said, the sound is clean and nice! will it give a good bass if i will connect it with the subwoofer filter?

  13. thanks seetherman ………. thanks a lot man …..

  14. Seetharaman

    Hi Lordsville As indicated 15-0-15 2000mA transformer will be 30VA normally. With a full wave rectifier it will give 15 volt ( a peak of 21volt DC)at 2Amp DC. even if you take full winding 2amps then it be just 60VA.If the efficiency of the amplifier is around 80%(cannot be this high) you can get 48 watts energy. that is just 24 watts per channel. For a good punch for a room of 20ft by 12 ft by 10 ft you require 60 watts RMS per channel for a good punch. You have to first upgrade amp and then the speakers. Amplifier rating can be always higher than the speaker capacity for a clean sound.

  15. Seetharaman

    Hi Omer the provider is correct he has given the best equivalents. you can go ahead.
    Hi Aris Once the assembly completed and thoroughly checked for mistakes, before energizing do not connect the speaker use a 100 ohms 10 watt resistance in its place. Temporarily link Q4 and Q6 bases. Now switch on with +35 0 -35 supply to the circuit without feeding any signal to the amplifier. check the current drawn by the circuit from positive and negative rail should be less than 50mA. the voltage across the 100 ohm resistance can not be more than few milli volts. if it is more check the connections and polarity of transistors and diodes, correct the mistakes and energize. If every thing is ok remove the base link by measuring the current at the collector of Q5 it should be between 60 and 100mA if not by varying R9 & R10 you can achieve. Once things are set feed around 50 to 100mV audio signal through a suitable volume control the sound should be clean and with life.

  16. hi sir seetharaman. i checked the Q3Transistor (2sb825 in place of 2n6107) and noticed that the pins were interchanged, i corrected it but when i powered it, it burned my 4ohms,80watts speaker. i checked the output voltage it sends the supply voltage when the speaker is connected. there is also a voltage at the input pin which is about 12volts dc.
    what happened sir. i never used my speaker before so i used it to test this project but sad to say it ended up burned.

  17. by the way sir,i used a cd player for testing but there is no output and when i touched the input terminal i still hear no blurring sound just like any other amplifier. hope you could help me solve it. tnx again sir!

  18. hello sir seethraman, i have built this amplifier but there is no sound coming out. ive used 2sb825 in place of 2n6107.2sd313 in place of 2n5294 and 2sd667 in place of bc108. i used .22 electrolytic at the input. all other capacitors and resistors used are those of specified. what might be wrong sir? i have not used those BD series but ill try to find it if those replacement i used are wrong. thanks in advance sir!

  19. hi mr. seetherman …..

    my question is personally for u….

    i m from pakistan and i didnt find any of the transistors used in this circuit but the provider gave me thier equivalent transistors … i did’nt have designed this circuit cz i want to confirm that these equivalents are suitable for the circuit or not ……..

    equivalents are as follows….

    2N3773 = 2N5303
    2N5294 = D313
    2N6107 = B857
    BC108 = BC109

    i will b very thankful to u ….. n will wait for ur kind reply… thnx.. 🙂

  20. lordsville

    hello evry1
    i bought an amp panel with a label :hi-ft ok 100w: powered by a 15v-0-15v 2000ma has an aux. Input and 2 mic. also has mic. Volume ctrl. Bass and treble ctrl and master vol. Ctrl. It works ok with 2×80-watts,6-ohms,5inch Sony deck speakers but Im not satisfied wt the audio depth and tnking of upgrading d speaker to 2x12inch double magnet subwoofer spkrs wt abt 8-ohm rated abt 200watts paralleled wt tweeters. Will it work wt my power supply and what modifications do I need to make?

  21. Hey seethraman thax a lot dude i repaced my transformer with a center tap 1 and its working well.
    Sound is not so clear wat replacements are to be made kindly tell.
    i replaced c1 with 4.7uf
    wat else to be replaced

  22. any ways 40volt is not to high for it na ?
    i will get it center taped if its ok

  23. no dude its a 28 volt 5amp transformer so 40 volt dc but not center tap
    thax a lot for the info i will try and let u know

  24. Seetharaman

    Hi Kingsly you require a centre tapped transformer 25-0-25volt of 125VA rating. speaker one should be connected to 0 volt other end of speaker to output transistors. you have to connect plus 35 volt as well -35volt to amplifier that is a total of 70 volt DC.

  25. tnx sir seetharaman. ill see if can get those replacement.

  26. do i need a center tap transformer for ground or normal 1 will work

  27. Hey seetharaman i have built this circuit but iam not geting any output at speaker my input is +40v 5amp
    i have connected the ground of my speaker to the ground of r1
    when i connect the ground of speaker to +40 input it give humms but no sound output
    my speaker is 8ohms 100w

  28. plzz plzz help me fast i will be doomed if it dosent work out

  29. the speaker is giving hum but no sound when the ground of speaker is given to +40 input

  30. Hey Seetharaman i am not geting any output my input voltage is 40v 5amp will it effect the circuit
    I have connected the speakers ground to R1 ground

  31. Seetharaman

    Hi Aris 2N6107 can be BD140, 2N5294 can be BD139 and 2N3773 can be BD182 or the standard 2N3055
    Hi Caloy if amplifier output and input terminal are close positive feed back can take place and you may get instability. the power supply input output terminals may not matter much they may produce little hum if filtering is not proper.

  32. wat will happen if the output terminal and the input terminal for power supply is near from each other???
    hum noise???

  33. are there any replacement for the transistors other than 2n series sirs?

  34. can i ask any substitute for all the transistors specifically sir seetharam?

  35. Thanx a lot jojo sir. . . .bt wil u plz b in touch wid me 2 clear my doubts. . .plz sir i nid ur help. . .sent me ur email id at . .n 1s again hearty thank u fr gvng me suggtn. . .

  36. Seetharam sir plz help me. . . .plz rply 2 me or atleast gve me ur email addr. .plz sir help me. .

  37. hey yar ………… can any one telL me that how can i able to convert 12V to 35 V dc????????

    i have 12 v transformer with 2A

    and another question …….. wilL this circuit work purely as a subwoofer output i.e with no stereo or voice sound only bass ??????????

  38. Seetharam wil u plz help me out in builting dis circuit. . .actualy m a beginer i dnt knw anythng but i hve very much interest in such circuits so wil u plz teach me i dnt even knw hw 2 read a cicuit diagram im a be 1st yr student of etc branch plz help me friend

  39. hey jeffrey, this is a difficult project for beginners.

  40. jeffrey castillo

    pwd hingi ng pcb design…. baguhan plang ksi ako guzto ko ma 22ng gumawa nang ganito

  41. is there any circuit which would give 35 volts from 12 or 24 volts

  42. Seetharaman

    Hi Tomin You are correct but you have to develop plus & minus dual supply for TDA2020 with inverter or other gadgets, but LA4440 is working with single 14 volt supply rail available in car and 19watts RMS inside the car is enough power for sub woofer.

  43. Seetharaman

    Hi Prem use Sanyo LA4440 for your application which is best suited as it produces 19watts RMS into 4 ohms speaker with quite low distortion.

  44. CT is quite awesome & informative…

  45. Could you please give me 12v supply sub woofer power amplifier…. For car stereo….
    Iam waiting for your reply…

  46. Hello sir,
    Could you pls give me 12v supply subwoofer amplifier circuit.. For car stereo…

  47. Seetharaman

    Hi Patrick you require a 25 – 0 – 25 volt 5amps this transformer will give you 250VA. use individual bridge rectifier and smoothing capacitors in each amplifier PCB to reduce cross talk. you require 5amp bridge with 2 nos 4700uF and 2 nos 0.1uF for each amplifier. run ac wires from transformer with not less than 18SWG wire to each amplifier.

  48. patrick vaz

    Power supply for 100watts subwoofer & 2×60 watts amplifier

    Hi Seetharaman,
    I want to have a common power supply for both the above mentioned subwoofer and 2×60 watts amps, what should be the transformer with ampere rating, power supply circuit diagram.

  49. Hi

    Does anyone know a link where there is a PCB design of this circuit.

  50. hi seetharaman

    I have assembled the circuit and working fine

  51. i am intersted to buy this circuit without power supply can any 1 intersted to send me i wl pay i am from India

  52. hello seetharaman

    you asked me for the voltages

    do the voltages are correct?

    At Q1 Emitter -1.2
    Collector 46.2
    Base -0.06

    At Q2 Emitter -1.2
    Collector 46.9
    Base -0.06

    At Q3 Emitter 46.3v
    Collector 1.2v
    Base 46.8v

    At Q4 Emitter 0.7v
    Collector 46.5v
    Base 1.2v

    At Q5 Emitter 0.03v
    Collector 47v
    Base 0.07v

    At Q6 Emitter 0.3v
    Collector -46.5v
    Base -0.1v

    At Q7 Emitter -47.4v
    Collector 0.03v
    Base -47.1v

  53. hello seetharaman

    At Q1 Emitter -1.2
    Collector 46.2
    Base -0.06

    At Q2 Emitter -1.2
    Collector 46.9
    Base -0.06

    At Q3 Emitter 46.3v
    Collector 1.2v
    Base 46.8v

    At Q4 Emitter 0.7v
    Collector 46.5v
    Base 1.2v

    At Q5 Emitter 0.03v
    Collector 47v
    Base 0.07v

    At Q6 Emitter 0.3v
    Collector -46.5v
    Base -0.1v

    At Q7 Emitter -47.4v
    Collector 0.03v
    Base -47.1v

  54. Seetharaman

    Hi Mounica they are not equivallents and cannot be used. 2N series is freely available hence can be used.
    Hi Jacob the circuit is correct as both the output transistors are NPN. Q4 and Q6 are complimentory drivers

  55. Hi seetharaman

    I think for Q6 100ohms resistor should be connected to emitter

  56. can i use BD139,BD140 or MJE340,MJE350 instead of 2N6107 and 2N5294

  57. hello seetharaman

    At Q1 Emitter -1.2
    Collector 46.2
    Base -0.06

    At Q2 Emitter -1.2
    Collector 46.9
    Base -0.06

    At Q3 Emitter 46.3v
    Collector 1.2v
    Base 46.8v

    At Q4 Emitter 0.7v
    Collector 46.5v
    Base 1.2v

    At Q5 Emitter 0.03v
    Collector 47v
    Base 0.07v

    At Q6 Emitter 0.3v
    Collector -46.5v
    Base -0.1v

    At Q7 Emitter -47.4v
    Collector 0.03v
    Base -47.1v

  58. please give your mobile number to talk with you personal

  59. Seetharaman

    with respect to zero volt at collector base and emitter of all the transistors and also across bias diodes

  60. Seetharaman

    Hi Jacob by shorting R9 and R10 if the current is not falling down check your circuit again and try to send me all the voltages, for me to understand your problem.

  61. Hello seetharaman output transistors getting too hot Q5 and Q7

    i adjusted bias current by trim-pot instead of R9 and R10 but still getting heat but drivers are running cool

    i have used 8inch length and 3inch wide aluminium heat sink was this sufficient?

    please solve this problem the amp producing too much heat.

  62. Hello seetharaman output transistors getting too hot Q5 and Q7

    i adjusted bias current by trim-pot in place of R9and R10 but still getting heat but drivers are running cool

    i have used 8inch length and 3inch wide aluminium heat sink was this sufficient?

    please solve this problem the amp producing too much heat

  63. Seetharaman

    Hi Jacob all other parts are OK go ahead building

  64. why dont you tell this first

    all the remaining part of the circuit is ok or not

  65. Seetharaman

    Hi Jacob C2 polarity is wrongkindly connect -ve lead of capacitor to R4 and +ve to ground.
    With the above correction it should become alright.
    if output is still going negative try adjusting R11 till it becomes zero.(give alteast 15 minutes for warming befor doing the adjustment).

  66. hello seetharaman C2 (4.7uf 100v)is getting bold and then it is exploding after several minutes why it is happening like this DC offset voltage is getting negative voltage

  67. i have used same as 40v dual power supply circuit appeared in this site

    what do you mean by regulated power supply

  68. if use it on Q4 what will happen?

    sorry for many questions

  69. Seetharaman

    Hi Jacob C2 is correct it is only the bypass capacitor for Q1 Q2 collector current.
    560 PF at Q6 may not have the required effect as it will give feed back to only one half of the waveform that is conduction through Q6, Q7 not through Q4, Q5.

  70. what will happen if i use 560pf at Q6

    if output DC voltage is 330mv do this spoil the speaker

  71. Seetharaman

    Hi Jacob capacitor C5 is used to roll of the high frequency response of the amplifier. it will be a negative feedback only at high frequencies. if increase the value the HF response of the amplifier will fall down as though you have cut the treble control. the value should be chosen such a way the amplifier response is limitted to audio frequency only( so that you can avoid HF instability)
    There wont be any change in the out put DC voltage only the AC voltage will change. if DC changes your amplifier power supply is not regulated properly. if DC is constant the amplifier is quite stable in DC conditions and it indicates the design is good.

  72. forgot to ask another question what is the use of capacitor C5
    please read above comment also

  73. seetharaman actually you didn’t understand my problem

    Problem 1:output offset voltage is increasing gradually before it was at 96mV but now it is around 380mV

    Problem 2:while playing songs at low sound the out voltage is same i.e 380mV.At maximum sound also it is showing same voltage how it is possible

    I am measuring output voltage with digital multimeter +ve terminal connected to K1 and -ve connected to earth

    Question:what will be the output voltage at full sound?

    please please understand my problem and question

  74. Seetharaman

    Hi Jacob you ar right. The gain of the amplifier is R6 / R5 that is 47K / 680 ohms. around 70. for 20 volt output you require only 20 / 70 = around 285mV RMS any pre amp will give you this much even the walkman or any digital MP3 player can give. check these resistance values and the capacitor C3. kindly increase the input coupling capacitor to 2.2 or 4.7uF 0.22 is not sufficient. Reduce C5 to 100PF. These should solve your problem.

  75. i have build this circuit (not assembled in a case) i have directly connected from cd player (not from sub woofer out) sound is good but getting low sound even at maximum volume i have used MPSA43 instead of BC108 because i don’t have them anyway this amp is very nice but low sound i think you can solve this problem

    output voltage is also increasing with out input signal at first it is 96mv but now it is 330mv

    when measuring output voltage while playing a song at maximum sound its voltage is same ie 330mv to 380mv
    For 100 watt it should get atleast 20v in multimeter

  76. Thank you seetharaman for your reply

    i have build this circuit (not assembled in a case) i have directly connected from cd player (not from sub woofer out) sound is good but getting low sound even at maximum volume i have used MPSA43 instead of BC108 because i don’t have them anyway this amp is very nice but low sound i think you can solve this problem

  77. Seetharaman

    Hi Jacob it requires a sub woofer filter. it can be connected directly to 5.1 DVD / VCD player’s sub-woofer output without any filter or preamplifier

  78. Hello Seetharaman

    could you please give me preamplifier circuit that it should have 2 AUX (100mV/470Kohms) and 2 Dynamic Mic inputs at 1K

    I request you the above circuit on 1st Aug,you told me that you will send soon but till now there is no response from you

    I am waiting for your reply

  79. seetharaman

    Hi JB you can refer to 40V dual power supply appeared earlier in Circuits today. use 24 – 0 – 24 volt transformer with 125VA rating, instead of 30 – 0 -30.

  80. seetharaman

    Hi JB You can use a 25 0 25 transformer with 150 VA capacity a 5 amp bridge rectifier and two filter capacitors of minimum 4700uF 50 volts with 0.1uF 100 volt ceramic capacitor in parellel with it in both positive and negative supply.
    rrefer to 40V dual power supply appeared in these column earlier

  81. Hi Seetharaman

    could you please give me preamplifier circuit that it should have 2 AUX (100mV/470Kohms) and 2 Dynamic Mic inputs at 1K

    I request you the above circuit on 1st Aug,you told me that you will send soon but till now there is no response from you

    I am waiting for your reply

  82. seetharaman

    Hi PravinSP sorry for the delay. the circuit enclosed is for your sub woofer filter. connect left and right channel input to this filter in addition to your LA4040 amplifier, and the output of the filter to subwoofer amplifier. The existing LA4040 will become your front right and left channels 2. and the subwoofer will be your .1 channel.
    you keep your LA4040 amps bass control little up so that it cannot respond to freq below 120Hz and enjoy the full thumping bass response.

  83. I had put an request on 23rd Aug 2010, I was wainting for your reply to start the project with..since then NO reply…Very Interesting…!!!

  84. sir, can you give me the power supply circuit so that its easy for me to assemble.. thank you.

  85. Hi Seetharaman, I want to make this circuit, I find it very insteresting as I have stereo amp made up of LA4440 and want to make a Subwoofer, to make my system 2.1. also tell me the circuitry for low frequencies, as input for 100Wtt Subwoofer Amp. Please could you send me it’s Clear Schematic and PCB to my mail ic –

  86. hello seetharaman i have send you mail( with attachment having circuit diagram of amplifier please read the mail and reply me soon

  87. seetharaman

    Hi Emmi Q3 also requires a good heatsink as being a driver transistor. 80volt pk tp pk avilable for the speakers. the RMS value becomes 28volt(ignoring the voltage drop across output transistors around 3volts) power = V sq / Z (spkr imp)
    28 X 28 / 8 = 98 watts approx. with 4ohms it will be 196watts(approx). Power supply must be capable of giving 3.5amps current. Fix a good heat sink for output transistors.

  88. A.A.ABDUL

    Hi seetharaman,pls i need a preamp 4 this diagram on my mail(

  89. Hi seetharaman

    i put trim pot between emitters of t1 t2 and adjusted offset voltage and also put 2.2k at r11
    sounds nice thanks for you reply
    but q3 is getting hot and q4,q6 are not getting is this normal

    i have put +/-40v to this circuit what will be the power rated at output how do you calculate

    can i use two 100watt speakers in parallel having impedance 8 ohms each

  90. seetharaman

    Hi Emmi fix a variable resistance temporarily for R11 say 5k 5W. adjust till you get zero voltage at out put. fix anearby preferred value. check the current drain of both supply rails without input signal itshould be within 100mA.

  91. hi seetharaman

    the out put is getting nearly 1 volt at no input this is very high how can i decrease this
    i think we have to add 100r in parallel with diode at emitter of Q6 to adjust instability of Q7 because its getting heat

  92. seetharaman

    Hi Pravinsp i was away on a pilgrimage and back. unfortunately my desk top is down. i can do drawing etc on it. now for email i am using my inspiron mini. please bear with me for few more days i will send you the circuit as well to Mr. Adnan on variable power pack.

  93. I had put an request on 23rd Aug 2010, it seems since then your were not online. I was wainting for your reply to start the project with..but on 30th Aug 2010, you were online and just one reply to Mounica…Very Interesting…!!!

  94. seetharaman

    Hi Mounica you can connect a zobel network (of 10 ohm in series with 0.1uF) in parellel to K1 loudspeaker.
    Vi limitter can be provided just before the capacitor C1.

  95. Hello seetharaman

    How can i add vi limiter and zobel network to this amp please tell me

  96. hi seetharaman i have build this circuit but Q5 is getting too hot at no input i found that voltage across r16 is high and also humm sound is coming

    why it is happening like that i checked everything all transistors are working perfect

    help me please

  97. Hi seetharaman i have build the above circuit the problem is q5 getting hotter and a humm sound is coming at output i found
    voltage across r16 is higher at no input

    what will be the problem ? i have checked everything all transistors are working
    help me please

  98. Hi Seetharaman, I want to make this circuit, I find it very insteresting as I have stereo amp made up of LA4040 and want to make a Subwoofer like 2.1 sound system also tell me how circuitry for low frequencies as input for 100Wtt Subwoofer Amp. Please send me it’s Clear Schematic and PCB to my mail ic –

  99. I found that voltage across the R14 is greater than R16 thats why Q7 is getting hotter than Q5

    If i increase the value of R11 (as you said) what will happen?
    voltage at R14 will decrease or not?

  100. seetharaman

    Hi Shreya increasing R11 to 2.7K to 3.3K should solve your problem.

  101. Hi seetharaman where you have gone all these days

    i shorted R9 & R10 the temperature of transistors decreased but Q7 is getting hotter than Q5 why ?

  102. Hello mr.seetharaman ur doin vry fine job by helpin people coz at times we are really clue less about the fault. so thanx a lot ………I wanted to ask u few things please suggest me …….i willb really thankfull to you
    iam makin this circuit and iam using transistor 6110 in place of 6107 and 5296 in place of 5294.
    please tell me will they work!! coz the actual values arent avialable here.
    and i have auto variable transformer which has a output range of 0-220 volts at its output it can give any o\p from 0 to220 volts and current ratig of 8 amps.please tell me how i can use this as it has no ground point. please tell me as soon as possible mail me if can .

  103. hi can i ask you something regarding in this circuit

  104. Hi seetharaman

    i found 3input mic pre amplifier
    can i use that for two amplifier if so how can i

  105. sir i have an strio amplifier circuit i want to build three chanal circuit 2 speeker and 1 woofer.
    spouse i have three mono amplifier in same condition.
    can you help me about it? plz
    how to convert my circuit for woofer?
    how to convert from 2 input to 1 out put?
    if you give me diagram i will be very very thanks

  106. Hi seetharaman
    i am asking about R8 not R9 and R10
    if i increase or decrease R8 what will happen?
    if i increase or decrease R13 and R15 what will happen?
    if i increase or decrease R14 and R16 what will happen?

  107. seetharaman

    This amplifier is a class B amplifier. that is it will conduct only when input sgnal is present(an ideal class b amp.
    If you use only D1 then if the input to out put pair is greater than 600 mV only it will conduct, up to that no conduction will take place. if you see the output waveform by feeding a sine wave input, the discontinuty at zero crossing. this is called cross over distortion.
    r9 and 10 are used to avoid the above phenomena by having a small conduction in out put pair. if you increase thiese resistance value the no input signal current through out put pair will increase. if you reduce the current will reduce but the cross over distortion may set in.

  108. Hello seetharaman
    i have some doubts could you please clarify
    this is what type(class) of amplifier?
    if i remove d2 what will happen?
    if i increase or decrease R8 what will happen?

  109. seetharaman

    Hi Mounica the amplifier will become Class A amplifier. Out put transistors require a very large heat sink.

  110. Hi seetharaman i shorted R9 & R10 the temperature of transistors decreased but Q7 is getting hotter than Q5 why ?

  111. seetharaman

    HiJoel MPSA 42 is a better transistor to 43. i will send soon.

  112. Hi seetharaman

    MPSA43 is not available can i use MPSA42?
    could you please give me preamplifier circuit that it should have 2 AUX (100mV/470Kohms) and 2 Dynamic Mic inputs my e-mail address

  113. seetharaman

    Hi David It is very high. please check the wiring around Q3, Q4, Q5. Q6 and Q7.
    My prototype consumes around 100mA standing current. (no signal current)

  114. Hi seetharaman i shorted R9 and R10 but the standard current is not reducing it is around 800mA what i have to do now

  115. Hi seetharaman

    what do you mean by standing current?

    the intake of current to the amplifier at +/- rail at no input signal right??

    please explain me i am new to electronics

    can you send your mobile number to my mail i have to ask some doubts

  116. seetharaman

    Hi KVS you can use. The DC will be 34 0 34 that is the most suited. if dc shown is x volts your transformer has to be x X 0.7, speaker impedance 8 ohms is preferable. 4 ohms can be used, use fast acting 5 amp fuse in both plus and minus supply.
    Hi Emmi PCB is not available. other project one is available on the net, which you can adopt. i will send it to your email id. The only standing current is adjusted to 50 to 75mA depends on the out put transistor matching, by varying R9 and R10 from 10 ohms to 27ohms

  117. Hello seetharaman
    Please read my comment dated July 29,2010

  118. hi seetharaman please reply me.
    i have 24-0-24v, 6A power supply.
    And my subwoofer rating 100w, 4.8ohm.
    May i use this power supply for this circuit?

  119. I don’t understand “put a link for R9 and R10” what do you mean by link?

    shall i shot them

  120. i didn’t have 35-0-35v transformer in my area.
    can i use 24-0-24v, 6A for this circuit?
    anybody reply me please.
    And i have 100w sub woofer & it shows 4.8ohms between it’s two lead.

  121. seetharaman

    Hi put a link for R9 and R10
    between C1 and R1 add 2.2 k resistance
    add 470 PF in parellel with R1.
    use a good quality shielded wire and connect to mp3 player through a 100k log volume control

  122. Yes seetharaman the output transistors are getting heated up without input signal

    Without any input signal the speaker is quiet but when i give input signal burring sound is coming

  123. seetharaman

    Hi Shreya whether it is burring sound or motor boating sound. Without any input signal the speaker should be quiet. Whether output transistors are getting heated up.

  124. sitharaman

    how to test this amplifier like adjusting bias current etc….

    you didn’t give any notes

    do you have PCB design? if it has can you send it to my mail

  125. Hello seetharaman

    i think R14 must be connected to collector of Q7 once check the diagram

    also tell me where should i use variable resistor of what value to adjust bias current

    sorry for my poor english

  126. Hi! seetharaman

    when i touch the input a barrrrrr sound is coming i thought that it is working but when i give input signal thru mp3player disturbance is coming and still barrr souund is coming
    i gave +/- 48v at 5 amperes to the amp
    please help me

  127. seetharaman

    Hi Mounica its quality is quite good. you please go through my earlier comments on the modification required

  128. seetharaman

    Hi Mounica it is a general purpose low audio frequency amplifier to be used with proper subwoofer filter

  129. Hi Seetharaman

    I already builts some subwoofer above but the audio result
    was not so good !
    Would you like explain me and answer my qustions :
    – what are we using the power rated subwoofer speaker same with the power rated output of the amplifier ?
    – why the quality of sound was different if i changed the input source,example tv and radio or many type of tv audio
    out ?

    thank alot

  130. seetharaman

    Hi David it is measured at the collector of Q5. Actual currnt depends of the component manufacturers production spread . All the specimens assembled cannot have identical values. To set it correctly feed 1KHz sine wave signal to the input of the amplifier and feed output to rated load and also connect it to an oscilloscope adjust the quiescent current till there is no discontinuty in sine wave at zero crossing point. it can be anything from 20mA to 200mA as per the matching of the compoung complimentry output transistors.

  131. Hi can any one give me circuit diagram of 2 channel to 5.1 channel sound conveter

  132. what is quiescent current actually ? How and where it is measured

  133. Hi Seetharaman,
    I want to know this circuit how output frequency in this circuit???????????????????????????????

  134. seetharaman

    Hi Shreya around 60 to 100mA depends on the components.

  135. Hi Seetharaman,

    Can you give me the circuit diagram of
    streo to 5.1 channel converter.

  136. I have an Infinity BU-120 subwoofer that has a bad amp. Can I use the factory installed RC connectors, off/on switch, phase switch and the like with this board?

  137. seetharaman

    Hi Soumya in 5.1 system you have to use 5 amplifiers and speakers. sub woofer will be a single channel amplifier only. low bass notes have no directivity they are not heard but felt. hence mixing both channels and using a suitable low pass filter you can get the low notes amplified through subwoofer amplifier. thisd project givs only the subwoofer amplifier portion.
    Hi monica you can use NE555 timer with the relay it has appeared in electronics today earlier.
    hi Shreya you can use this for any application as i informed earlier only a small modification is required, increase C1 to 4.7uF and reduce C5 to 47 to 100PF. before C1 provide a volume control

  138. Hi Seetharaman

    can i use this amplifier for keyboard and guitar

  139. Hi seetharaman

    can you please give me the circuit diagram of five seconds timer

  140. seetharaman

    Hi Monica initially you will be connecting the amplifier output to a resistance, for the output coupling capacitor inside the amplifier to get charged. In 5 seconds it will get charged. once it is fully charged you can connect the amplifier to speaker without the click problem.
    to do this automatically when ever you switch on the amplifier, the resistance will be connected to the amplifier output through the timer, once the required time is lapsed the timer will connect the speakers to the amplifier by disconnecting the resistance.

  141. Hi seetharaman

    i didn’t understand whare i have to connect 100ohms resistance and switch

    please explain me

  142. seetharaman

    Hi Shreya you can use any transformer with 1.5 amp are greater. 1.5amp is sufficient. if you have 5 or 10 amp you can use it. still at higher volumes the consumption cannot be more than 1.5amps. Then why we prefer the current rating. since if you inadvertently short the amplifier output nothing will happen to the amplifier with higher rating transformer the current drawn by the out put transistor can reach the maximum capability of the transformer and will get destroyed to avoid it use a fast acting 1.5amps fuses in the power supply both positive and negative supply rail.
    Hi Mounica A simple solution will be conect the speaker through a switch, first connect the amplifier to 100 ohms resistance and switch over to speaker after 3 to 5 seconds, this will enable the out put coupling capacitor to get charged and the thump can be avoided.
    You can also use a 5 second timer to do this job.

  143. Hi seetharaman

    i have an ahuja 100watt amplifier when i switch on a big sound “pat” is coming out of speaker how can i prevent this sound


  144. Hi Seetharaman

    can i use this amplifier for keyboard and guitar

    also need some clarification about using transformer
    i have 35-0-35 5A transformer
    i will use 16ohms load
    but you told to joe to use 1.5A
    because i don’t have 1.5A
    if i use 16ohms load at 5A any problem will occur please let me know clearly

  145. Soumya Sumitra Behera

    And also sir cant we have volume control for it.
    I connect Front speaker=10Wx2, Reer speaker=10Wx2 and center=10W.

  146. Soumya Sumitra Behera

    Sir, i really really thanku from my heart. Thanku for your kind circuit diagram. Can u please tell me the name of the parts-(What-resistor, capacitor, diode, IC chip). I cant understand from the c.diagram. Pls tell me what will be preferable for input voltage? Can i use simple circuit board which have many holes in it and we have to solder? Where should i connect front and reer speaker pins? Pls teach me in detailed…Pls…Pls…Pls

  147. seetharaman

    Hi David check the polarity of bias diodes D1 and D2. short R9 & R10 and check the standing current, may come down to just few mA, without any signal input to amplifier. at low volumes it may sound highly distorted. you can adjust these values to increase the standing current to 50mA or so. By shorting R9 & R10 if the current not reducing, then there is some wiring mistake kindly check up thoroughly.

  148. Soumya Sumitra Behera

    Dear Sir,
    I gota 30 W, 4 ohms speaker for sub-woofer. I am going on scarping my head. I dont know how to construct the amplifier for it. This sub-woofer is going to be used in 5.1. Please show me the way to construct this. Please provide me your kind guidance, by the circuit diagram and the parts to be used and where to be used. I am a beginner. Pledging your kind reply.

  149. Dear sitharaman

    Thanks for your kind reply

    i found that bu407 is npn and 2n6107 is pnp

    anyway i changed to 2n6107

    but the transistors which are in the output(Q5 and Q7) are getting to hot

    when we touch the heat sink our finger will burn out that much heat is coming from them

    it is getting hot with in few seconds

    i am using 32-0-32 5A transformer

    let me know what changes have to be made to the circuit

    reply as early as possible brother..

    thank you

  150. seetharaman

    Hi David all your component selections are ok. 40 volt power supply published is the correct one only change is you have to use a 25 – 0 – 25 @ 2.5amps transformer. Q1 & Q2 you may use only BC107 or 547 not BC108(some samples may fail).

  151. Dear sitharaman

    i have used BU407 instead of 2N6107
    For R2&R5 i have used 560 ohms instead of 680
    For R4 – 4.1K instead of 4.7K
    For R7,R9,R10 18ohms instead of 22ohms
    For R11 1.8k instead of 1.5K
    For R13&15 120ohms instead of 100ohms
    For R16&R14 i have used 0.5ohms instead of 0.33

    all these are changed due to lack of availability

    Please Help me it is not working to me
    i have checked many times but no use

  152. Dear sitharaman

    i have center tap transformer but when i connect to +35 -35 and ground its getting shorted my fuse burnt out

    i have seen the circuit diagram of 40v in this site done as it is but it happens as stated above

    what i have to do now please tell me .
    is this ciruit is correct?

  153. seetharaman

    Hi David You require a total of 70 volts DC with centre tap. Hence with reference to Zero (common) you should have both positive 35 and negative 35 volts. like operational amplifier plus minus 15 volts.

  154. Dear sitharaman what is +35 and -35 can i combind those please tell me

  155. seetharaman

    Hi Nirmal you have to use a pre amplifier since the amplifier requires around 400mV RMS input for the rated output.
    If you want to use this as an exclusive sub woofer amplifier increase C1 to 4.7uF and use an active sub woofer filter before the amplifier

  156. seetharaman

    Hi Shreya since he is going to use 15 ohms speaker 1.5amp is sufficient for 8 ohms load you require 3amps rating. you can comfortably use 5amps transformer.

  157. hai is there is any pre amplifier need for this circuit

  158. Hi Seetharaman

    So i can use 35-0-35 5 Amperes Transformer by changing Q1 and Q2 with MPSA43 Right?

    But you stated to Joel dated July 7 1.5 A

    can i use 5A for single amplifier

  159. seetharaman

    Hi Shreyas upto 200watts you dont require to use any parellel transistors.
    any way to parellel out put trasistors connect both bases together connect both collectors together. but for emitter for each transistor use a seperate 0.33 ohms resistance. this will protect the transistors from thermal runaway.

  160. seetharaman

    Hi Shreya This amplifier is a general pupose amplifier. To make it into a sub woofer amplifier you have to use the sub woofer filter. If you want to use it as a general purpose amplifier increase C1 to 5uF and reduce C5 to 47 to 100PF.
    35 – 0 – 35 transformer will give you a no load voltage of 35 X sqr 2 = 50 volts. It will be quite high, you refer to my reply to mr.joe dated 6th july for the required modifications.

  161. Hi Seetharaman

    is this amplifier can be used for speakers
    what changes have to be made can you tell me please

    and also how can we add two more transistors along with same model of Q4 and Q7 to share the load

    can you suggest me the transformer like how much amperes should i use

    i have ’35-0-35 5A Transformer’ can i use this for the present shown circuit
    please tell me

  162. seetharaman

    Hi Joel Higher the load impedance – higher voltage, less current to get the same power. A 1.5 Amp transformer will do for a single amplifier.

  163. Thankyou Seetharaman

    So i have to increase only supply voltage.

    Then what about current 5A is enough???


    i want to use this as normal amplifier not as subwoofer amplifier so what changes have to be made

    and also want to add two more transistors to Q7 and Q5 with same model to share the load

    i don’t know how to do it can you please tell me

  165. seetharaman

    Hi Joel you can use higher than the rated impedance speakers with any amplifier, only thing is the available power will get reduced. In this circuit it will get reduced to 45 to 50 watts. To increase you have to increase the supply voltage to plus minus 55 volt and replace Q1 and Q2 with MPSA43. use all capacitors with 63 volt or higher rating

  166. i want output load to 16ohms can any body tell want changes have to do to this circuit

  167. k. i want that time delay line circuit. the above attachment will not open.

  168. seetharaman

    Hi KVS you can use a direct signal mix with delay signal and use a single amplifier. but to avoid inter modulation and distortion problems I always use a spare amp for delay line. the delay line is required to give the reverbration of a big hall. so your existing room will look like enlarged into a big hall or auditorium. this is called commercially as echo effect. there are bucket brigade chips available for different time delay line.

  169. so i create another circuit to another woofer for theatre effect? what can i do for a small time delay circuit in the second 100 watts amplifier with woofer? please send that time delay circuit to me. my mail id

  170. seetharaman

    Hi KVS It will reproduce heart thumping beat. But for theatre effect you require a small time delay circuit in the second 100 watts amplifier with woofer.

  171. is this circuit produce theatre effect? that i mean heart beat thumping? with 8inch,100w,rubber woofer? in 15*15feet room. please send reply for me mr.seetharaman.

  172. seetharaman

    Hi Gouranga you have to use center tap transformer and a bridge rectifier with minimum 4700uf capacitor in both positive and negative power supply
    By increasing C1 to 4.7uf you can achieve response down to 20Hz.

  173. how mach frequency this amplifier respond?
    is there need bridge rectifier in power supply?
    or how connect the power supply in to the amplifier?

  174. seetharaman

    Hi Nayak
    All Capacitors to be of 50 volts rating. This amplifier as such can respond to voice also may be upto 6KHz it can respond. Hence you have to neceesasorily use the sub woofer filter to take care of it. Increase C1 value to 2.2 to 4.7uF.

  175. Basanta Nayak

    what is the voltage of all capacitors. also any one tell me that the amp. outs only bass. no voice. or outs voice also?

  176. seetharaman

    Hi Chris The second wire should get connected to the 0 volt of +35 & -35Volt. similarly the input side ground also should get connected to 0 volt of the power supply. the input socket common also should get connected to 0 volt of the power supply and to the metal chassis as close to the input socket as possible. (power supply o volt should not get grounded anywhere else except near the input socket as indicated). If your home theatre has got subwoofer output connect it to this amplifier. To get 100watts output use 12″ 4 ohms impedance speaker, front mounted in 20mm thick wooden cabinet of inner volume not less than 35litres.

  177. hi, I am planing on building this circuit to go along with my old home theater system. can you post or send me a parts list of all the components I will need and some tips on building it.
    I also see that the speaker has only one wire going to it. where is the second wire? If it is a ground wire, do i connect both ground wires together, then ground it?

  178. seetharaman

    Hi Allan low frequencies are not heard, but felt by our body. in my experience a clean 100watts (as per DIN45500) of bass is more than sufficient to be felt in a room of 3000 cub ft.

  179. sir, why does our output is so small that we can only hear a sound about 40hz? how can we make our output sounds better?

  180. seetharaman

    Hi this amplifier is designed as a sub woofer amplifier to cover low frequecies only, you have to use this after the sub woofer filter. but can be modified easily as a full rane amplifier also.
    you can use a 100Kohm potentiometer in the input. slider connected to C1 and cold end of the pot to common, input signal between hot end(other end of the pot) and cold end of potentiometer. increase C1 to 2.2 or 4.7uf non electrolytic capacitor to improve low frequency response to 10Hz or so, with the present value the roll of will be above 50Hz itself.

  181. Is there a volume Control?
    Is the diagram of the circuit in the picture a design to work as a subwoofer (120 hz and below),or is it designed to cover all frequencies( about 80 hz-20,000 hz)

  182. seetharaman

    Hello Gannex this is the best tone control circuit. you can add it before the sub woofer amplifier at C1 (‘in’ signal)with its own power supply as it uses only a single supply. reduce C5 between 47 to 100PF, if you want to use this amplifier as an independant hi-fi installation, not as sub woofer amplifier.

  183. Hello Seetharaman, thank you for your advise.
    I found this tone control at and i want to integrate this in the circuit. Where should i connect the input and output of the tone control? Is it in series between the output of Q1 to the input of Q3 (not Q2 sorry)? Or just to place the tone control before the input of the 100W Subwoofer Amplifier? Thanks you.

  184. Hello Seetharaman, thank you for your advise.
    I found this tone control at and i want to integrate this in the circuit. Where should i connect the input and output of the tone control? Is it in series between the output of Q1 to the input of Q2? Or just to place the tone control before the input of the 100W Subwoofer Amplifier? Thanks you.

  185. seetharaman

    Hi connect a tone control network before the main amplifier with its own power supply. you can use a simple passive tone control and add a transistor amplifier with a voltage gain of 50. if you want to use the same power supply use suitable regulators and tone control circuit with dual supply. these circuits are availabe on the net

  186. Hello Guys!
    I just would like to know if is it possible to add Bass & Treble control in the circuit, perhaps using a potentiometer? How and where to place the controls? Thank you very much.

  187. seetharaman

    Hi Anthony Deane are you supplying both +30 and -30 volt(total supply voltage is 60volts). if so it should work. The groud indicates that it should be connected to zero volt reference. Q3, Q4 & Q6 require a small cooling fin each. For Q5 & Q7 use a good quality extruded alloy heatsink insulate them using available ready made kits.

  188. hi,
    Is this circuit is for subwoofer only?what i mean is,is output only low frequency no high frequency coming out?i want to build this circuit,is there any one can guide me,

  189. Anthony Deane

    Hi Guys,
    I Build the 100w subwoofer circuit and power it with 24v 4amp transformer, which when rectifies gives an output voltage of 30v dc. My problem is when i test the circuit with this 30v, it send an output signal to the speaker and then stop.
    I then test back all the components on this circuit which test o.k, but i am not geting back the signal to the speaker.what advice can you give me, one more thing how to layout the output transistors do all them have to moumt on the same heat sink insulated properly.

  190. Anthony Deane

    Can You please send me the power supply diagram for the 100w Subwoofer project.

  191. seetharaman

    Hi Suku you can use a 100Kohm potentiometer in the input, slider to C1 cold end to common, between hot end and cold end of potetiometer input signal. Except C5 no other feed back or filters are used. this can give a good frequecy response upto approx 8KHz beyond 10KHz it will be rolled of. For a hi-fi application you can reduce this to 47PF add 1Kilo ohms with 470PF input filter to amplifier. increase C1 to 2.2 or 4.7 micro farades poly carbonate capacitor.

  192. Hi
    Can you tell me what is the range of frequency response and any way to control the output like using pot or so

  193. hello admin,
    To obtain +35v&-35v,which type of voltage rating step down transformer can we use?

  194. Seetharaman

    Dear Ram Iam using this amplifier as an Hi-Fi amplifier at home. Hence the suggested improvements. To use as a sub woofer amplifier for which it is designed leave C5 as it is. increase C1 to 2.2mfd poly corbonate capacitor. with 8 inch venyl rubber surround woofer in 25 litre infinite baffle gives eccelent thumping bass reproduction. assemble and listen to believe it.

  195. Seetharaman

    Yes Mr Ram
    This simple amplifier is really sounding very good you need not have any doubt about it. If you use good practice in laying out the components the given circuit will work very well. You may require small improvement depends on your layout. You can provide input filter with 1kohm resistance in series with the input and by passing it with 470pf to common. This will limit the amplifier responding to frquncies beyond audible range (simple low pass filter) You can connect 100mfd electrolytic in parallel with 0.1 mfd ceramic capacitor to positive and negative supply rail close to power transistors for power supply decoupling due to long inter connecting wires if used. After these modifications If you feel high frequency response is little lesser reduce C5 to 100 to 150PF. wishing you happy listening.

  196. is this cricuit working????????????
    or any correction is requried

  197. is that 10k (R8) is include….
    is that connected to base of Q4..

  198. realy fentastic site this one, very very thanks to you ……
    so many new ideas from here. thank you…

  199. twits4twats

    Is this Circuit Working ?


    The circuit looks like it will work allthough I haven’t built it myself. This uses a high pass filter and a class A amplifier. Active filters are a better solution and the only resistors that require a higher wattage rating are R16 & R14.

  200. hi buddies….mukba from georgia
    amplifier is excellent,great
    if u have any questions you can ask me

  201. ian cabajar

    can we use an 8 ohms speaker for this amp.?

  202. ian cabajar

    what is the voltage of all the capacitors? electrolytic and ceramic

  203. how do you connect the heat sinks to Q4 and Q7 and why heat sinks are required here??

  204. IS there anything else that can power this circut other than 35v.

    • 35V is necessary for getting the full output power. Reducing the supply voltage will reduce the output power.

  205. hi i have made this circuit i am having some kind of hum sound in this i need to know wats the problem in the circuit and should i use mica for output transitors to the heat sink can u pls guide me

  206. I have 35 0 35 secondary transformer and the rectified output shows around +47 0 -47..

    Is it suitable to connect for this circuit.

    • YED KRiz

      USE 25/0/25 VOLT RMC AC @ 3 AMPS,THIS WILL PRODUCE +36/0/-36 volts DC best suited for this amplifier.

  207. wat type of capacitors are c2&c3 resistors whose wattage are not specified must be 1/4 watts is’nt it

    • C2 and C3 are electrolytic capacitors.
      The resistors with unspecified wattage are 1/4 watt resistors.

  208. neto oliveira

    gosto muito de projecto amplifier e outros

    fortaleza brasil

  209. Tende ivo

    I must say I’m very proud of this site but i will be very glad to hear you say whether the circuit needs a power transistor or not
    and how it is connected.
    I am waiting to hear from you people.

    • the transistors used in the final stage are power transistors itself.

      • sir, pls send a complete layout of your 100w sub-woofer amplifier. i am very interested to make and assemble this circuit.thks & happy new year.

      • g’eve sir, .,if you have time plsss send me the pcb layout of this design!, .,thanks much!

        • SEBIN JACOB

          seetharaman sir,

          I want a stereo amplifier circuit.The 150 w amplifier using tip147 in your site and this circuit, which will work fine which one gives the good sound clarity and good output please help me.I am already using this circuit as a sub woofer amplifier it works good.if i want to double this for stereo amplifier how much amp transformer i must use is 5 ampere enough.