Circuit Schematics Diagrams and Projects

300 Watt MOSFET Real HI-FI Power Amplifier

 300 Watt Mosfet Power Amplifier schematic


My passion for excellence progressed over the past 40 years to developing sonically superior amplifiers to the highest possible standards, providing life like sound performance.

I am committed to sharing my experience of the RAS 300 with other enthusiasts sharing my passion for perfection.I designed this minimalist amplifier to be durable, simple to operate while offering high fidelity equivalent to the original sound source and would recommend partnering this amplifier only with other products of outstanding quality.

When I set out to design this amplifier, my aim was to create a product most suitable for the reproduction of complex music and speech signals. Although I placed high emphasis on electrical characteristics, the single most important requirement is achieving an audibly superior sound, vivid spatial imaging and superb tonal clarity.

Although the average listening level is normally less than 10 watts, my design approach was to create an amplifier with ample reserve power, but biasing it for class A at average listening levels reducing cross-over distortion to extremely low levels.

There is not one capacitor in the signal path, improved the accuracy of the tonal characteristics of instruments and voices significantly.
The RAS 300 has almost zero phase distortion far beyond the audio range resulting in perfect resolution and totally un-coloured sound.

Amplifier Specification:
Maximum Output: 240 watts rms into 8 Ohms, 380 watts rms into 4 Ohms
Audio Frequency Linearity: 20 Hz - 20 kHz (+0, -0.2 dB)
Closed Loop Gain: 32 dB
Hum and Noise: -90 dB (input short circuit)
Output Offset Voltage: Less than 13 mV (input short circuit)
Phase Linearity: Less than 13 0 (10 Hz - 20 kHz)
Harmonic Distortion: Less than 0.007% at rated power
IM Distortion: Less than .009% at maximum power


The amplifier consists of two completely separate monaural amplifiers each channel has its own power supply, resulting in zero inter-channel cross talk, a common phenomenon in amplifiers sharing the same power supply.

In order to obtain the full output power each supply transformer should be rated at 40VAC - 0 - 40VAC at 640VA. Unlike many designs relying on the reservoir capacitors to supply peak currents, I prefer to have the raw power available from the transformer resulting in much faster transients.

Although the RAS 300 specifications are moderate, when listening to it you will immediately experience the massive reserve power available and never have any cause of anxiety that something is going to give in that one would when driving many amplifiers loud.

You will hear nothing but reality with no distortion at any level and I guarantee that this amplifier will divulge the best qualities of any equipment connected to it.

You can download the PCB layouts and the part list files from here

A Final Word from Author Nico,

I invested thousands of work hours into developing and refining the RAS 300 making use of advanced computer simulations, test equipment and the of course a vast variety and number of human ears.

I have found to my surprise that many listeners I invited to audition the equipment who normally does not enjoying listening to music, actually changed their perspective completely when exposed to this system.

Of course speakers, inter-connections and source does play a significant role in the final result. However, the choice of speakers and music is like your choice of fine wine, it is what you enjoy.

I am convinced that you would be as pleased and proud owning this amplifier as I am designing it, never finding the need to upgrade as it will provide you with many of years of listening pleasure.

Author: NICO RAS from Diyaudiotr 

Comments (57)

why does your circuit diagram was uncleared? other than that, can we use bipolar transistor instead using mosfet as power output of your amp?
daniel kyei boadu
i need pwer amp similar but it sould be only transisters
Greg Smith
I saw power amplifier similar at Ebay.
Vergel Calma
Hi,i assembled your amplifier and it sounds good. Is it possible to add some additional mosfet output to increase it's power? My driver speaker is 18 inch 1200watts.
true 300 watt rms power amp circuit diagrame plz send me
Dirk Steyn
I'm keen to try this project. Just know that this will require a huge heatsink, but how will it be placed on the MOSFET transistors?
i want to build the amp, and am very pleased with the circuit. you have really done a great job, keep it up. and i hope to learn more from you on amplifiers. writing from malawi. isnt it possibe to increase the supply voltage to /-65V
rayedgwapo gundoy jr
is the power output transistor in this circuit could be replace by another is it a quasi or complimentary symmetry amplifier
what is the replacement number of power transistor 2sj162 and 2sk1058,how much the ampare we can use the trasformer of this circuit
hi i love to build this circuit,can i use also bipolar tranies, instead, of mosfet for power output?
Vicken Mardiros
just need to try if it works and i'll mail u back
Bruce Lavender
380 watts into 4ohms from a -/ 55volts impossible Mr ras you need to go back to school!!!! who are you fooling you sound like a glorified
hi fi sales man. I wont even waste my time explaing why cant get 380 watts from -/ 55 volts. A local crowd make a simalar circuit the company is called PA&L they use /- 60 volt supply and it just manages to do 250 watts into 4 ohms.
hi bruce lavander! wat do u mean, the ras 300 is impossible to get 380 watts at 4 ohms? of /-55 volts supply can u help me,im newly of electronic and i want to buil,this circuit from m. ras 300,wat do u think why mr. ras 300 post. this cicuit,
Why iget your komponen for power amplifier 300wat (fet)
suresh R
How can i get this(300w mosfet amplifier)assembled kit and what is the cost of this
hi suresh, there are no kits available.
hahaha!!!!!it sounds good....more power!!!!
Bima Shah
i have 12" 120mm megnate full range speakar,is it possible to connect 2no 12" 90mm megnate ? is it compectable ? can u give me any speakar combination for better out put? with network circuit if require & give me some idea for making speakar box ,what i do for better out put? if you have any tone control pcb designe for stereo plz reply me and send me its pcb designe if you have .....Thanks
I can't se capacitor C2 in the partlist, should it be there or not?
thnx for the nice project, what type of loud speaker i have to use fo the cicuit. plz let me know.
hi !I would like to assemble this circuit and I really appreaciate of what you did to complete this project of yours,can you proved to me that this realy works good as you said?Thanks and more power to you!
i think bruce is must be /-80 volts get the exact 380 watts into 4ohms...
joey de leon
is there an easy way to do this using few components?
Sherwin de vera
Pls. Send me the pcb board lay out and parts list i like this amp.Pls thanks.
stephon marbury
if anyone was able to build this, can you tell me how much is the total harmonic distortion? maybe there are some components that we might overlook that causes this distortions...
Somebody haves the pcb layouts, the link on this page appears to be dead. Thanks a lot.
this amplifier have a clear sounds, no hum or noise,good amps. I ask about the rated Ampere of the power it Ok to use 40 volts centertap at a rated of 15 ampere? the mosfets have carry this high current? because on the data sheets only 7 ampere maximum current of this mosfets.
when I build this I replaced the driving transistors,to low frequency. wala ako masabi this is a great sound like audiophile amplifier,if you increase the power add the mosfets. but this mosfets have higher cost unlike the other.
somebody planed to build this amp.look the transistorr output something wrong..I have many redisign this amp to make sound. I put the supply 35 35 center tap.15 ampere the mosfets become heat in standby mode, I think this is a 100 watt rms,if you like more power I think add 2 two mosfets to negative supply and positive supply so 8 mosfets at all that a higher cost. thanks
i want to build 1200 watts power amplifier can u give me the circuits diagram
if you build 1200 watts u can used this schematic just add 3 K1058 and 3 J162 then supply a 100 voltsDC Peak,total 200 volts peak to peak. then the four driver medium transistor change in high power handling
pow((55V/sqrt(2)),2)/4ohm = 378W
i tried using 50 volts dc 15 ampere transformer the transistors become heat.I think someone used an big heat sink to prevent over heating the mosfet
Given the topology of the proposed circuit layout on the PC board, how do you attach a large heatsink to the FETs? Example:
Emmanuel Darko
please where can i get the n channel and p channel mosfet transistor
circuit is totally wrong, dont go for this circuits. output MOSFET quiescent current setting made with two diode series connection, so MOSFET will be cutoff all the time, Output MOSFET need minimum 2.5V for passing quiescent current of 100mA. So this circuit will not work at all. Author: NICO RAS from Diyaudiotr grabbed this circuit from some other site and redesigned his own. So worst.......
Built this circuit, running off 57 - 0 - 57 DC, connected to 500W 15inch speaker, sound is excellent and pumps the bass with no problem.Mosfets cooled on good 180mm L shape to amp box. Cool mosfets with 2X computor fans with heat sensor switch attached. Good amp with high power.
This amp pumps, mosfets cooled by means of fan on heatsink. good power.
good power.runing off 57 0 57DC,no problem, 500w speaker connected, this amp pumps.
Federico Peris
Why the ground of the input its conected to the (-) of the speaker in the pcb, and not in the schematic???...thanks..
i completely build this amp.i using ac 24 0 24.dc go to 35 0 35.bass not power i can get full bass?and what max voltage of this amp?
Bruce needs to re-examine the circuit's power supply.
With a + AND - 60V power supply you have 120Volts.
A 120 volt sine wave multiplied by .707 gives the RMS
value of 84 volts. Put that into a 4 ohm load and ya get
1764 watts !

Plug your 4 ohn speaker into a wall socket and yer gonna need a 3500 watt speaker !
This circuit is built successfully, however, with 55V you can not expect 300W rms. In fact, theoretically +-70V would give 240W into 4 ohm load, but the small transistors should be replaced with 100V equivalents as previously Nico Ras in his site as RAS240. Anyway, the max power supply voltage can not exceed 63V, because of mosfet failures. So, like any other copy and paste circuits you can not build that circuit with just a small piece of information. Instead, ask Nico Ras, or goto Rod Elliott's site for a similar project, Rod and Nico well each other this is their mutual project derived from Hitachi application notes.
It's surprizing that the project was stolen and put here without permission form the author. Ant not the least, some wannabe diyers commented in a way that reflects their lack of common electronics knowledge. Why don't you bother trying to reach the author and ask your questions or negotiate your concerns? Mr. Nico Ras is a great guy when it comes to sharing experience and has been in to audio for more than lifetimes of many of you. You can probably reach him form
hi,good day, is 1/4 watt and 2 amp diode used for the amplifier ras 300???????
hi good day,hmmmm,the transistors are expensive.if this project wont work,waste of money hehehe but i will try to make one
I have built this amp but it's not switching with the stated supply voltage.However with + and -20Vdc am getting good output.What could be the problem?
I like the symmetry of the design and have seen the first circuit from a hitachi app note using 2sk134 and 2sj48 I think. These devices have a negative temperature coefficient so no thermal compensation for the bias is required. ETI published an amp based on the hitachi app note in the early 1980's. I think it was called old smokey.I like the design so much I built for units using parts from my junk bin.
I have just switched this amp on and am really impressed with the performance. I am running +/- 60v DC Supply (pushing it a bit). It sounds great and have had it on the signal generator and scope and output seems nice and flat all the way. I must say a word of thanks to Nico Ras for putting this design on the net. I photographed and manufactured the board and built and tested 2 channels in just over 3 hours.The mounting arrangement works very well and have added fan cooling that kicks in at 40 degrees. A anti thump relay is a must and a led vu meter adds a bit of flash.
I built old smokey back in the mid 80's. It was a great amp and I would still be using it today if it hadn't been stolen when my house was burgled!
with 35-0-35vdc works just fine.But with 56-0-56 it starts distorting. why?. please assist me
shailendra kumar patel
i'll built that ckt but that was not working can u tell me what is the fault in it
hi i have a harnest on this mosfet 300 i need to know what are the speaker wires and so forth. i have a green a white a blue a orange and a yellow 5 wires can you help me
i like to go for this project because its very simple......
who like the bass should try this amp.bass very dynamic.very simple amp.but higher cost of power output.i using for my 12" subwoofer.
if you like quality sound and power, then try this out
I think that your circuit needs output short-circuit protection or shutdown. Can you design it in, please?

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