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DIY 100 Watt MOSFET Amplifier Circuit

Last Updated on by 88 Comments

MOSFET based amplifiers as we all know are outstanding with their sound qualities and they can easily beat the performance of other counterparts based on power transistors or linear ICs.

Why use Mosfets in Amplifiers

However amplifiers based on mosfets are not always easy to design or make.

Moreover after assembling a prototype, testing to perfection always remains an issue with new electronic hobbyists.

You might have come across many hi-fi complex mosfet amplifier designs, but might have not dared making it just because of the above reasons.

The simple mosfet amplifier circuit diagram is super simple to build and yet will provide you with a crystal clear 100 watts of raw music power that all the listeners will cherish for a long time.

The idea was developed a long time ago by the Hitachi researchers and still it remains one of the favorite designs of all time considering the involved simplicity against quality.

How the Amplifier is designed to Function

Looking at the figure we can understand the circuit with the following points:



The involved simplicity would also certainly mean that some of the ideal features of the circuit was sacrificed in the design, for example it lacks a constant current source for the differential amplifier at the input stage of the amplifier.

However that doesn't induce any serious problems though.

The differential amplifier makes sure that the input is sufficiently amplified to some reasonable levels suitable for feeding the next driver stage.

The driver stage consists of a well balanced high voltage transistor stage which are necessarily positioned for driving the output power mosfets.

The pot positioned in between the two sections of the driver stage is used for setting the quiescent current of the circuit.

The output stage is a common push pull type of mosfet stage which finally provides the boost for amplifying the fed low signal music into a 100 watt thumping music over a 8 Ohm speaker.

The shown parts might be obsolete today so may be replaced as follows:

The differential transistor may be replaced with BC556.

The driver transistors may be replaced with MJE350/MJE340.

The mosfets may be replaced with 2SJ162/2SK1058

 

Parts List

Resistors

All resistors are 1/4 watt, CFR 5%, unless otherwise stated.

100 Ohm = 7nos

100k = 1no

47k = 1no

5.1k = 2nos

62k = 1no

22k = 1no

2.2k = 1no

12k = 1no

1k = 1no

4.7 ohm = 1no

0.2 ohm / 5 watts = 4nos

Capacitors

All capacitors must be minimum 100V rated

1uF = 1no Electrolytic

100uF = 3nos Electrolytic

15pF = 1no Polyester

30pF = 1no Polyester

0.22uF = 3nos Polyester

0.0068uF = 1no Polyester

Semiconductors

Q1, Q2 = BC546

Q3 = MJE350

Q4, Q5 = MJE340

Q6, Q7 = 2SK1058

Q8, Q9 = 2SJ162

1N4148 = 2nos

Misc

Inductor = 1uH, 20 turns of close wound 1mm super enameled copper wire, with 10mm diameter (air core)

Note: The resistor, and capacitor values are not critical, slight up and down will do, and will not cause any harm to the performance of the amplifier

Parts, PCB Images and Prototype

1) The first image shows the PCB which was used for the 100 watt mosfet amplifier circuit project

2) The second pic shows the soldered portion of the assembled circuit.

3) The third pic illustrates the components side of the assembled board

4) The fourth image relates with a  few of the components involved with the the circuit making.

5) The fifth figure witnesses the speakers which was used for testing the amplifier with astonishing levels of clarity and superb power outputs :p

I used only a couple of mosfets which could generate power outputs well over 100 watts RMS, connecting more numbers in parallel can easily enable this circuit to cross beyond the 1000 watts mark.

If you are intending to buy a ready made power amplifier for your home, I would suggest, you build this one instead and be the proud owner of this outstanding home built power amplifier unit which would probably serve you for years.

 

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Reader Interactions

Comments

  2. Hello dear swagatam ji
    I'm a Mechanical Engineer. I am unable to find the name of some component and specifications.
    It is my request to you plz share the complete list of component with their specification.
    I will be very great full to you.
    Thank you

    Vivek

    Reply

  4. one of the best electronics sites and Swagatam you are the greatest blogger, electronics PRO i have ever came across bcos i really really appreciate you support for a new beginners in electronics like me and lots of others bcos you give us hope by answering our questions because a pro like yourself will never ask questions which we the beginners in electronics don't understand and needs helps, YOU ROCKSSSSSSS, SIR KEEP UP THE GREAT WORK. BTW i have a 400watt-RMS mono mosfet amp and the required VDC is 56-0-56VDC its very hard to find even a 45-0-45VCD so i am wondering why can't pro's like you and others design an amp like car amp which uses a 12-0-VDC no matter how big is the amp wattage, because this is just a 100 Watt MOSFET Amplifier but the downfall is the power it requires is 56VDC and as i said even a 45-0-45VDC SMPS based power supply is very hard and expensive to get out here in our country India anyways thank you sir you are a great and a very kind man too, appreciated.

    Reply

    • Thanks Lima, I am glad you liked my website.

      Amplifiers and inverters are generally rated with higher operating voltages so that the current (amp) rating could be lowered….as we know that Watt = V x I, that implies if the voltage goes low, the current has to rise and vice versa.

      Lower voltage and higher current spec would mean the amplifier getting bigger and bulkier in size and unnecessarily heating up.

      This is why the above explained 100 watt amplifier could be directly upgraded to 300 watt amp simply by increasing the operating voltage to 75V or 90V…

      conversely if the above amp was operated with a 12V then the current required would had to go up to 100/12 = 8 amps, causing a substantial amount of heat generation and involving large heatsinks.

      Therefore to avoid this high watt devices are preferably powered with higher voltages and lower current supplies.

      Reply

    • You are most welcome. OK, so HIGHER-VOLTAGE+SMALLER-AMPERAGE=LESS-OVER-HEATING of the amp yes(: maybe this is the reason why i see most car amps no matter what the brand is, it gets hot because of less-voltage it uses(like 12VDC car battery) anyways Thank you so very much Swagatam for this great info and great site, for some couple of years i totally lost interest in electronics because the only info i am able to get is from the net (i don't get much time to go to electronics training institutes because i am employed) but as you know, guys out there who publish articles based on electronics, they never answer our questions but sir you just gave me new hope to continue learning electronics. Keep up the great work for new beginners like me and all around the globe.

      Reply

    • that's right Lima, it's the amps that is responsible for generating the heat….just divide watts with volts to get amps and try to keep this as low as possible in any power circuit.

      you can feel free to comment here and share your thoughts with the folks around and me.

      Reply

  5. Ok then I will try but in the mean time I have all the parts and I keep trying to make it work, I even tried in on a new bread board with new wires thinking it was a connection problem but still nothing, the only time I hear a hum of any sort is when I use my finger to touch the zener diodes I hear a hum from the speaker, I was wondering If I should just build it on a Vero board because I reall need it this week and a pcb will take so long because of my location, I am wondering If I should just use the parts from the older version in the circuit in this article

    Reply

    • In bread board the possibility of a connection fault is more likely than on a PCB….moreover mosfets prefer short connections and therefore work better on correctly designed PCBs.
      Veroboard can also be problematic due to their closely etched pads which can cause hidden short circuits or stray inductances

      Reply

  6. I am going to pull up the circuit I built on the proto type board and start again and ensure no mistakes. I have never done a Pcb so I am not even sure which way to go using that method I normally use Veroboard. A Pcb Manufacturer needs gerber files to make a board and the pic in the article its file is Gif So I am assuming I have to converter it to gerber to submit to a website

    Reply

    • OK, that'll be fine…provide the downloaded zip file to the PCB manufacturer, that should be enough for him to convert the given info into a practical PCB…if ot then you can approach some other more efficient source

      Reply

    • still it should have worked, please follow exactly what's mentioned in the referred linked article…you can download the PCB layout and try the amp on the PCB, just as I did for my prototype and succeeded

      Reply

  8. Some Parts are different but lets Ignore that, what I am saying is the Pcb would need to be improved because I would need to step up to power from 100w to atleat 2000w so I would need more FETS, you didnt reply to that

    Reply

    • technically, both are exactly identical.

      you said your basic circuit did not work, so first succeed with the basic 4 mosfet version and then you can think of upgrading it for higher outputs.

      Reply

  9. the reason I didnt try the version you had was because in the comments I think you refered someone to the original designer of the circuit for the updated version so I tried it. also I actually want to add mire Fets to it because I need a 2000W amplifier unless I could just use the pcb for the first section of the circuit and the place added fets seperate

    Reply

    • the circuit which I referred has a recommended PCB with it…actually both the circuits are one and the same, in fact the linked circuit was inspired from the above original circuit from Hitachi

      Reply

  10. I built the newer version of this amp from the article but I am not getting any sound out I use only 1 pair of Fets to test it I am using Irfz44n and Ifr4905 the Ifr4905 gets slightly warm when its plugged in but I cant seem to find my fault in the wiring if I hold the signal wire and touch the ground itself I will here a slight hum from my speaker connected but thats all, also I only powered it from 14v +/- for testing purpose.

    Reply

    • When I built it started working immediately with extremely high clarity and super high volume.

      you will need to use the recommended PCB and all the parts as given in the original design for enabling a proper working of the system

      Reply

  11. Hi Dear, This looks a very nice project to me will try soon.
    Some question to pacify me:
    1. Is this sound better than BJT
    2. What class this is?
    3. Will OP/AMP 072 tone circuit will improve quality over 741?
    4. Will 10000uf/63 Volt do or have to increase uf for better result.
    5. Can PCB be availed by you.

    Tks
    Lalit

    Reply

    • Here are the answers:

      1) sound quality cannot be better than BJT, but mosfets can save space as these are capable of handling huge power compared to BJTs.

      2) I am not sure about the class…could be classB

      3) our ears won't be able to make out the difference between 741 an 072 quality

      4) same as above

      5) PCB is not available with me.

      Reply

  13. Hi Swagatam,

    I tried with input and output open (ie without grounding) and also connecting the bulbs before the circuit.But still the 0.2 ohms resistor at Q7 started to produce smoke. I feel that my component rating is not right (may be lower value).so I request you to provide me with the righr resistor,diode and capacitor ratings.

    Thanks

    Reply

    • Hi Aaron, the 0.22 resistor should be 3 watt rated and rest all can be 1/4 watt.

      all capacitors must have a voltage rating that may be twice of the supply voltage, meaning if you are using 50-0-50V, then the capacitors must be rated at 100V each

      However even if you connected 0.22, 1/4 watt it should not have burnt with a small bulb in series with the supply terminals, here's the image of the bulb you must try with:

      http://www.newmodellersshop.co.uk/images/grain_of_rice_bulb.jpg

      These are also known by the name "rice bulbs"

      Reply

  14. Hi Swagatam,

    At last I have assembled the ckt but before I could set the quiescent current the 0.2 ohms resistance started to smoke. Kindly give me

    a detailed parts list(mentioning Ohms-volts/watts).I have used the following components

    Resistors
    1. 100 ohm (8 nos)
    2. 0.2 ohm 1watt (4 nos)
    3. 4.7 ohm 1/4 watts (1 nos)
    4. 22k (1 nos)
    5. 5.1k (2 nos)
    6. 2.2k (1 nos)
    7. 47k (1 nos)
    8. 12k (1 nos)
    9. 62k (1 nos)
    10. 1k variable pot (1 nos)

    Capacitors

    1. 0.22u (3 nos)
    2. 100uf capacitive (3 nos)
    3. 0.68 (1 nos)
    4. 15p (1 nos)
    5. 1u (1 nos)
    6. 30p (1 nos)

    Inductor :- 1u (1 nos)

    Diode:- 1N4148 (3 nos)

    Transistors

    Q1 & Q2 – BC556
    Q3 – MJE 350
    Q4 & Q5 – MJE340

    Mosfet

    Q6 & Q8 – 2SJ162 and
    Q7 & Q9 – 2SK1058

    Power supply
    24-0-24/5amps transformer

    Please give me full spec (ohms/volts/watts) for each components.

    Warm Regards,
    Aaron

    Reply

    • Hi Aaron, I guess you have used the previous original circuit which had a 1k preset adjustment, OK in that case you can follow the following procedure.

      Use two tiny bulbs rated at 100mA 24V or 50V, connect these in series with the (+) and the (-) input supply terminals, such that the supply passes through these before reaching the circuit.

      When switched ON you will find these bulb lit up brightly….now you simply need to adjust the 1k preset until the bulbs just shut off….the quiescent current is set now.

      the above must be conducted with the input of the amp shorted to ground and the output open.

      alternatively you can replace the preset with two 1N4148 diodes as shown in the diagram and simply avoid the above hassle…….

      Reply

  16. Hi Swagatam,

    Thanks for the info and now about the heat sink can u advise me as to which transistor needs heat sink and also can u tell me how to make a crossover for both high and low frequencies. Thanks in advance.

    Reply

  17. Hi, Swagatam

    Thanks for directing me to this page I wanted to add a treble, bass and volume control for the above circuit can u tell me how it can be done and about the supply for the above ckt I just have a 24-0-24,5 amps transformer will this power be sufficient and if it is…can u help me with its rectification ckt diagram.Thanks in advance.

    Reply

    • Thanks Aaronz,

      for bass/treble you can try the 741 stage circuit shown in the following image:

      http://3.bp.blogspot.com/-ymKuHf69dDk/UdmW_ybzAeI/AAAAAAAAEzk/sELvs1XZJY8/s1600/spectrum+analyzer+circuit.png

      The C8 output can be then linked with the the input of the above mosfet amplifier through a 10k pot, this pot will then act like a volume control.

      the center lead of the pot will go to the amplifier input lead, one of the outer leads of the pot can be connected with the ground of the supply, and the other free lead of the pot can be finally connected with the C8 out of the bass/treble stage.

      for a better response pin4 of the 741 IC can be linked with the (-) of the supply instead of the ground which is shown in the bass/treble diagram.

      24V-0-24V will be OK but will genearte only 120 watts, for higher watts upto 500 watt you may try using 100-0-100V trafo. but make sure the bass/treble stage does not get more than 15-0-15V for the IC 741

      Reply

    • A 100-0-100V transformer or smps based power supply will be very hard to get out here in India, even impossible too. Swagatam why not give us a Simple 100Watt-RMS amp which uses a 12_0V like car amp does. Thank you.

      Reply

  20. hello
    i just need to get some things straight about the circuit because they're confusing
    -what is the component right after the input? the 1u valued one? is that a capacitance too?
    Q6,7,8,9 are mosfets while the others are bjts?
    is 0.068u capacitance a preset value available for purchase or do i have to make it somehow?
    and finally, what input should i put in exactly? how do i input a sound?

    sorry for the many questions but i really need help with this 🙁

    Reply

    • hello, nothing is confusing in the diagram.

      yes it's a capacitor (electrolytic)

      mosfets and BJTs can be easily distinguished from their symbols.

      all components are readily available.

      put music input from your cell phone.

      Reply

    • also i tried checking the site you mentioned in another comment to understand the part replacements but i didn't really get it :/
      are these replacements correct?
      Q1 & Q2 – BC556
      Q3 -?
      Q4 – MJE350
      Q5 – MJE340
      Mosfet
      Q6 & Q8 – 2SJ162 and
      Q7 & Q9 – 2SK1058 ??

      Reply

    • It's a preset which could be replaced with two 1N4148 diodes connected in series back to back, anodes up, cathodes down.

      yes all the components are correctly selected for enabling high voltage operations,
      upto 100V

      Q3 = MJE350
      Q4/5 = MJE340

      Reply

  24. sir can i use 4 pair of IRF540 and IRF9540 to replace the output mosfet (if it will be then can you guess how much watt would i get @ 50 0 50

    Reply

    • connect two small (low current) incandescent bulbs in the path (series) with the (+) and (-) supply terminals, short he speaker terminals.

      Now apply power, adjust the preset until the bulbs stop glowing.

      Reply

    • sir ,
      correct me if i am wrong.
      short means i should connect speaker o/p to ground.doubt sir,By shorting this would blowoff the MOSFET?
      is 0 watt incandescent bulbs is enough?

      Sorry sir if you get annoyed
      I am confused, I gone through the both circuit you provided(100Watts)and the link 300Watts. Both Circuits are different.
      which circuit i should make.

      The link you provided (100watt) In that O/p of amplifier is connected by inductor 1 micro henry.is it necessary to place that coil? how to make it?

      Reply

    • thanks a lot sir,
      coming to my build amplifier using IC 4440 . I check the voltage its giving 18 volt DC but i am not sure about the Current.
      Sir How can i check the current of transformer .Transformer dimension is 3 inch by 3inch. Yes by size we cant judge the o/p current
      regards

      Reply

    • connect a DC ammeter in series with any of the power supply terminals.

      switch on the amplifier and set the volume at optimal levels, and you would be able to see varying current consumption on the meter, you can take the average of the readings……

      Reply

    • Please check their datasheets online for current and voltage. If volt handling capacity is above 100 and current above 8 amps, then it would be OK.

      Reply

  39. Hi, Swagatam
    This is very Simple Diagram. Part list is vey complicated, I doubt these are avialable nowadays.
    According to you the equivalant are like this I guess..for
    Q1 & Q2 – BC556
    Q3 -?
    Q4 – MJE350
    Q5 – MJE340
    Mosfet
    Q6 & Q8 – 2SJ162 and
    Q7 & Q9 – 2SK1058 Please Correct Me..
    For L1 can it be hand wound?
    and for Power Supply I have 12-0-12 5Amp Transformer.

    Reply

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