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  • 2500


This pair of F-4 Clone Boards use the same circuit as the Nelson Pass / Firstwatt F-4 model.

Circuit description

The F4 is a Push-Pull, Class-A, Mosfet power amplifier. It is unique in that all of the active devices (transistors) are connected in a 'source-follower' configuration, which makes the amp add very little sonic coloration to the signal, less coloration than most other arrangements.

It sounds very, very good, and is extremely versatile, as each channel can be used separately, or a stereo amp can be run balanced for high power. This is a current source amplifier - it can run any normal speaker, but the F4 needs a preamp that has voltage gain - a passive preamp or buffer will not drive an F4. This amp has no voltage gain so works best when paired with an active preamp that has reasonable gain.  Most preamp circuits from the 50's - 80's will have enough, and there are a number of DIY designs made specifically for the F4 as well. It can also be used on the output of a "flea-powered" tube power amp, keeping the tone of the tubes, but adding power enough to run normal speakers. The sonic signature of the F4 is as close to completely transparent as can be built - the tone of whatever you use to drive the F4 will pass though without any alteration.

Please read the Firstwatt F4 manual for more explanation on configurations and use, availiable at

Populate these boards with your own components, then add your own power supply, chassis and heat sinks to complete the amplifier. These generously sized, high quality boards spread the six output MOSFETS for efficient cooling. The mounting hole spacing is the same as all other diyAudio Version 2 UMS boards.

Output Power

  • Running as a stereo amplifier from a single-ended source, 25WPC into 8ohms
  • A stereo amp, running as a Monoblock from single-ended source, 50W into 8ohms
  • A stereo amp, running as a Monoblock from balanced source, 100W into 8ohms

Power supply requirements

A Bipolar power supply of (+/- 24V) is required. This will require an 18V+18V (or 36V Center Tapped) transformer from 300-500VA, and PSU capacitance of 60,000uF per rail or more. The PSU for the F4, F5, and Aleph J are all essentially identical. See the F5 build guide for details. (F4 guide coming soon!)

Chassis Suggestion

The 4U Deluxe Amplifier Chassis makes a great home for this amplifier, and has pre-tapped holes that match the circuit board and transistor mounting positions. The diyAudio "Universal Mounting Spec" (UMS) is a common mounting pattern between the amplifier PCB and the heatsinks. If you utilize the UMS on your heatsinks or use one of the pre-drilled chassis from diyAudio, you will be able to quickly and easily mount different amplifier boards in the same chassis. For example, a 4U 'Jack of all Chassis' with a 400VA, 18V+18V transformer and PSU board, will give you a power supply and chassis where you could try the F4, F5, F5C, Aleph J, and other Pass/Firstwatt amps in the future merely by swapping the amp PCB. The investment in Chassis and PSU needs only be made once.

Build Guide

An Illustrated build guide showing all sorts of useful information on how to build your F4 can be found here: F4 Build Guide


Please see the F4 thread in the store support forum for any questions you might have and a definitive list of relevant links and resources.

Additional Information 

Dimensions 250mm x 50mm
Mounting holes UMS Heatsink Compatible
Number of boards included 2
Layers 2
Board Revision 2.0

Customer Reviews

Based on 9 reviews
What can you do with a coefficient of 1?

Well, you'd be surprised how much you might do with this no gain amplifier. You should read up on it and if it seems you'd like to give it a try you will be rewarded with a new and lovely perspective.

It will show you what you need to know about your preamp. It will show you how a speaker can be really controlled. I use mine to drive a pair of high efficiency sub woofers because of the control afforded. It is a great tool in making music and taking a full assessment of where your stereo is at. I have built the F4, F5t, F6 and the Aleph J, all very good experiences and all still in service but the one that taught me the most about stereos is the F4.

All of the kits here are a great bargain and very well made. The gift from Nelson Pass and his supporters is not to be passed up. Build this amp! You'll be educated and it'll be fun!

Great design, excellent quality.

The amp itself is brilliant design!
PCBs are of excellent quality and very easy to work with.
Though a couple of improvements can be made: bigger diameter of resistor leg holes allow to install high quality resistors like 0.5W Shinkoh or Takman. Also it's better to bypass electrolytic caps with film and mica caps, so place for one (or better - two) bypass caps for each electrolytic should be great addition.

Great Amplifier

I first bought an F5 kit from DIY audio store. It was an awesome sounding amplifier but I felt it had too much gain for my system (I have very sensitive speakers). I then got the F4 amplifier PCBs, that I could use in the same chassis I used for the F5 (I had to augment the PSU with another board for more capacitance). The F4 is perfect for my system, I don't have to listen at very low volume setting anymore butt I still do have plenty of room to increase volume if needed. The sound is great. The F5 has exceptionally fast transients and a somewhat lean sound with tons of details. The F4 has a more relaxed presentation, not as fast as the F5, but I felt the sound has very wide soundstage, and the details are still there. Very enjoyable to listen to. Overall I am very happy with this amp, that I know will remain in my system for a long time. I am very pleased with the service from DIY Audio Store, and the quality of the PCBs and parts they provide. Thank you!


Everything was ok, fast shipping. Highly recommend.

DIY Audio Store

Excellent products. Fast shipping.

As good as it can be!

This time my shipment was held up at Indian customs for a while & I received the goodies on 14th Feb 2K18 (Had to pay a hefty customs duty)
No complaints about the goods though! Excellent quality & good packaging as well. A big & hearty "Thank You" to all at DIY Audio Store - MM

the f4boards are A1

I've built a bunch of stuffs starting more than 40 years ago. An with these pass projects things just keep getting better and better. And easier and easier. I don't want to miss lead you, I build tube stuff too, and really love them. They are awesome beautiful art works, elegant and unique. Instruments of music, not reproduction. They make music. Sand amps though, - they are different, and you gotta accept this, but then guys like Allen Wright and Nelson Pass come along, and they've change everything, - for the better, more artful. And this is the accomplishment of our time, to bring back art to this increasingly artifical man-made world. And the more of it we make the not so always better. Man, the times I was born into, guys in the bowery were throwing shit on canvas and calling it art. Well we changed that, now its a wonder to see and hear also again. I've seen art, real art become Ordinary, and I've looked on as we become more artful, and creative without animus, with pathos or love or our collective identity in mind. It makes me wonder if Barack Obama is really John the Baptist. IF so the man is on the way, let the trumpets roars, the Man is on his way. Anyway when I am listen to these amps, the F4's I can think of these thing and ideas together. I can wonder and dream, and can also think the thoughts that can recreate the dream on earth. Both ways are valid and in the right frame of mind together they are a bit of heaven on earth.


fast and as expected.

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