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Please note we have F6 parts / transformer kits now available (which include a pair of these PCBs).

These F-6 Clone Boards use the same circuit as the Nelson Pass / diyAudio FirstWatt F6 described in the diyAudio FirstWatt F6 thread thread.

This set of circuit boards will make a MOSFET version of the F6 amplifier of Nelson Pass. This amplifier is a new and interesting development from his creative mind, where a small collection of parts comes together to make amazing, beautiful music. This creativity and solid engineering has kept Mr. Pass, and his companies, Pass Labs and FirstWatt, at the forefront of specialist audio engineering and construction, where new and wonderful creations are made.

The original amplifier utilized extremely rare power JFET from SemiSouth, which will never be made again, and are all gone. Be warned, any eBay sources claiming to have the SemiSouth devices are fakes. If you happen to already have the power JFET, they can be used with this PCB.

Populate these boards with your components, then add your own power supply, chassis and heat sinks to complete the amplifier.

Circuit description

The F6 is a Class-A MOSFET power amplifier, with a JFET driver stage. It utilizes a small-signal transformer for phase inversion, so both the output MOSFET are N-channel. This transformer greatly contributes to the overall sonic character of the amp which is very highly regarded and considered to be similar and having all the benefits and positive characteristics of a tube amp... making some observers speculate that much of the positive 'tube amp' sound is the transformers, not the tubes. The F6 is a regular kind of amp - a voltage source amplifier, requiring nothing out of the ordinary from the preamp or the speakers.

Output power

As with most of the FirstWatt amplifiers the power output is 25WPC into 8 ohm. More into 4 ohm.

PSU requirements

A Bipolar power supply of (+/- 24V) is required. This will require an 18V+18V (or 36V Center Tapped) transformer from 300-400VA, (shielded transformers are preferred) and PSU capacitance of at 60,000uF per rail or more. A PSU for the F4, F5, or similar will be appropriate. See the F6 build guide for details.

Chassis (heatsink) requirements

The 4U 'Jack of all Chassis' is ideal for this amplifier. If making your own chassis a good rule of thumb is at least 25sq inch (160sq cm) of finned heatsink per output transistor. (More is always better.) 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 the diyAudio store, 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 the F6 can be found here -- F6 Build Guide


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

Customer Reviews

Based on 17 reviews
F6 vs F5

I decided to build the F6 after doing and listening to the F5 for a few months. Although the F5 is a fantastic sounding amp I somehow found it a tick too bright and flashy...
Now the F6 seems to be a completely different beast (in a positive way) as it sounds darker and rounder.
Only a few hours of listening but I guess I'll stick to this one ;-)
Absolutely fantastic service from DIY as always.


F6 boards
They are high quality.
the finish of these boards have been great!


Hi quality PCB with plenty of empty space, i.e it could have been made a little more compact.
Power in, and output to loudspeakers would benefit from being a little more separated allowing for nicer cable routing.
Anyway these are not big issues and the overall impression is great!

Super Amp

This is my second F6. Sound is like a good tube amp but better bass response. I am very happy again.


Good quality. Will do business again.

F6 boards

They are high quality. I’m still in process of building but the finish of these boards have been great!

Very sweet sounding amp

Easiest by far, needs bare minimum adjustments, very very quiet. I remember a very old tube radio from my Grandpa's time, it does sound much like it. Vocals are simply amazing and puts up a great soundstage. Listening for 6 months now, coupled with BA-3 frontend pre, trying various types of music, it keeps getting better and better. I was thinking of making Aleph J during Christmas, but going to postpone it for some more time...for a year atleast :)


Very fast delivery and customs clearance. The best heat dissipation for the IRFP240 is "Keratherm-red",
thermal conductivity: 6.5 W / mK.

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