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300 Watt MOSFET Real HI-FI Power Amplifier

Project Summary

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.

Project Description


Figure 1 

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.

Project Files

File NameFile Size
PCB layouts and parts files376.57 KB
Tags: MOSFET, HI-FI, power, amplifier,

Comments on this Project:

By ken -2Score: 

7 years ago:  why does your circuit diagram was uncleared? other than that, can we use bipolar transistor instead using mosfet as power output of your amp?

By daniel kyei boadu 2Score: 

7 years ago:  i need pwer amp similar but it sould be only transisters

By Greg Smith 0Score: 

7 years ago:  I saw power amplifier similar at Ebay.

By Vergel Calma 0Score: 

7 years ago:  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.

By ali 0Score: 

7 years ago:  true 300 watt rms power amp circuit diagrame plz send me

By Dirk Steyn 0Score: 

7 years ago:  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?

By RICHARD 0Score: 

7 years ago:  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

By rayedgwapo gundoy jr 0Score: 

7 years ago:  is the power output transistor in this circuit could be replace by another is it a quasi or complimentary symmetry amplifier

By joe 0Score: 

7 years ago:  what is the replacement number of power transistor 2sj162 and 2sk1058,how much the ampare we can use the trasformer of this circuit

By jun 0Score: 

7 years ago:  hi i love to build this circuit,can i use also bipolar tranies, instead, of mosfet for power output?

By Vicken Mardiros 0Score: 

7 years ago:  just need to try if it works and i'll mail u back

By Bruce Lavender 0Score: 

7 years ago:  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.

By jun 0Score: 

6 years ago:  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,

By deddy 0Score: 

6 years ago:  Why iget your komponen for power amplifier 300wat (fet)

By suresh R 0Score: 

6 years ago:  How can i get this(300w mosfet amplifier)assembled kit and what is the cost of this

By jck 0Score: 

6 years ago:  hi suresh, there are no kits available.

By williampadilla 0Score: 

6 years ago:  hahaha!!!!!it sounds good....more power!!!!

By Bima Shah 0Score: 

6 years ago:  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

By ludde 0Score: 

6 years ago:  I can't se capacitor C2 in the partlist, should it be there or not?

By ibnul 0Score: 

6 years ago:  thnx for the nice project, what type of loud speaker i have to use fo the cicuit. plz let me know.

By jigz_ianzy 0Score: 

6 years ago:  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!

By stitch 0Score: 

6 years ago:  i think bruce is must be /-80 volts get the exact 380 watts into 4ohms...

By joey de leon 0Score: 

5 years ago:  is there an easy way to do this using few components?

By Sherwin de vera 0Score: 

5 years ago:  Pls. Send me the pcb board lay out and parts list i like this amp.Pls thanks.

By stephon marbury 0Score: 

5 years ago:  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...

By Ronaldo 0Score: 

5 years ago:  Somebody haves the pcb layouts, the link on this page appears to be dead. Thanks a lot.

By ryan 0Score: 

5 years ago:  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.

By ryan 1Score: 

5 years ago:  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.

By ryan 0Score: 

5 years ago:  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

By willy 0Score: 

5 years ago:  i want to build 1200 watts power amplifier can u give me the circuits diagram

By john 0Score: 

5 years ago:  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

By johnman 0Score: 

5 years ago:  pow((55V/sqrt(2)),2)/4ohm = 378W

By john 0Score: 

5 years ago:  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

By Steve 0Score: 

5 years ago:  Given the topology of the proposed circuit layout on the PC board, how do you attach a large heatsink to the FETs? Example:

By Emmanuel Darko 0Score: 

5 years ago:  please where can i get the n channel and p channel mosfet transistor

By Niyas 1Score: 

5 years ago:  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.......

By gerard 0Score: 

4 years ago:  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.

By gerard 0Score: 

4 years ago:  This amp pumps, mosfets cooled by means of fan on heatsink. good power.

By gerard 0Score: 

4 years ago:  good power.runing off 57 0 57DC,no problem, 500w speaker connected, this amp pumps.

By Federico Peris 0Score: 

4 years ago:  Why the ground of the input its conected to the (-) of the speaker in the pcb, and not in the schematic???...thanks..

By ariff 0Score: 

4 years ago:  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?

By Johnny56 0Score: 

4 years ago:  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 !

By DiyaudioTR 1Score: 

4 years ago:  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.

By diyaudiotr 0Score: 

4 years ago:  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

By james 0Score: 

4 years ago:  hi,good day, is 1/4 watt and 2 amp diode used for the amplifier ras 300???????

By james 0Score: 

4 years ago:  hi good day,hmmmm,the transistors are expensive.if this project wont work,waste of money hehehe but i will try to make one

By julius 0Score: 

4 years ago:   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?

By Rupert 0Score: 

4 years ago:  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.

By Rupert 0Score: 

4 years ago:  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.

By Rik 0Score: 

4 years ago:  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!

By chales 0Score: 

4 years ago:  with 35-0-35vdc works just fine.But with 56-0-56 it starts distorting. why?. please assist me

By shailendra kumar patel 0Score: 

4 years ago:  i'll built that ckt but that was not working can u tell me what is the fault in it

By dwight 0Score: 

3 years ago:  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

By yogeshmani 0Score: 

3 years ago:  i like to go for this project because its very simple......

By ariff 0Score: 

3 years ago:  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.

By knights 0Score: 

3 years ago:  if you like quality sound and power, then try this out

By richard 1Score: 

3 years ago:  I think that your circuit needs output short-circuit protection or shutdown. Can you design it in, please?

Ian Fearn
By Ian Fearn (+9) 1Score: 

3 years ago:  Hi the output devices you have used are now very hard to come by could you please nform me of an equivlent that will not destroy the very good published specification of this amplifier. I have yet to check to see if there are any problems obtaining the other semiconductors in this amplifier .. Please advise as i am very intrested in building this amplifier. I dont need such high power so i would like to run it on say +_ 35 Vdc and use only one pair of output devices.

Kindest Regards Ian (.(JavaScript must be enabled to view this email address))

Mark Harrington

3 years ago:  Good design however having spent many years servicing amplifiers class A, class AB , Class GH , Class D I notice that in all designs except for the odd few that No loudspeaker protection has been introduced into the design equally No Clipping protection , further no AGC , No Over current protection and no Over vaults protection Now as silly as this may sound There isn’t one manufacturer bar the odd few and I do mean the odd few that ever thinks about this at all Whilst of course the market is flooded with such amplifiers all resembling very much the same as yours in circuitry The most common fault is short circuit outputs especially Fets and bang lost of DC at very high currents through the loudspeakers and in the case of pwm or dc to dc power supply stages this then becomes even more critical where some how the manufacture designer then also forgets that they need earth isolation so consequently DC up the phono inputs under certain fault conditions and bang goes the next peace of equipment that is connected to your amazing design

I very good suggestion which I hope you will take note of please incorporate this into your design lest we should see more companies fold, more court cases and some very annoyed customers knocking at your companies / designers door Food for thought “Why have we got such a problem with technical standards in the UK , USA and elsewhere ?? “ Be different for a change produces something that is in the interests of the customer and not just for your back pockets Your customer base will improve tenfold if you do and you wont have to replace speakers under warranty saving all of us many arguments not to mention wasted time and money and keep people employed must be a bonus I would have thought

Krzysztof Kowalewicz

3 years ago:  Ian
I have build similar but not the same amp utilizing mentioned 2sk1058 and 2sk162. The sound is really very clear and dynamic. Unfortunately there is no replacement for it - only original or post production from china. Be aware that 2 pair are due to improve transconductance! (resistance of one pair is to high for 4 ohm speakers) I have checked it. I also recommend you decrise of 470R resistors connected to gates. 100-200R are ok.
good luck

Masood Alvi
By Masood Alvi (0) 0Score: 

2 years ago:  i made its pcb but i am unable to fit mosfet with heat sink.can any one send me kit picture

Masood Alvi
By Masood Alvi (0) 0Score: 

2 years ago:  300w nico ras amplifier gallery

Swagatam Majumdar

2 years ago:  I have build the above circuit, it works outstandingly well.

The sound quality and the level of amplification is awesome.

The important thing is that it started working immediately after assembly without any fuss....

You may see the built prototype here:

Oliver Carlos
By Oliver Carlos (-1) -1Score: 

1 year ago:  What if i use 38v-0-38v @ 8amp what power can i achieve at 8ohms and 4ohms speaker system

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