This site has limited support for your browser. We recommend switching to Edge, Chrome, Safari, or Firefox.

Power Amplifier project by Nelson Pass


Another unique amplifier in the First Watt family from Nelson Pass. The F6 is a Class-A MOSFET power amplifier, with a JFET driver stage. It utilizes a small-signal transformer that greatly contributes to the overall sonic character of the amp.



From $ 24.00 USD
2 options

Key Information

  • Power Amplifier Project
  • Designed by Nelson Pass
  • Intermediate Difficulty
  • Only Essentials Kit Available
  • Basic Build Guide


  • Another incredible First Watt Amplifier
  • Unique use of a signal transformer

Links, Discussions & Files


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

25WPC into 8ohm

Power supply requirements

A Bipolar power supply of (+/- 24V) is required. The PSUs for almost all First Watt amplifiers including the F4, F5, F6, M2x, Aleph J, and Aleph Jzm are all essentially identical.

These Power Supply PCBs are suitable for all First Watt amplifiers.

Chassis suggestions

We have a full line of Deluxe Chassis perfect for this project. The two most common choices are the Deluxe 4U and the larger Deluxe 5U, however we heartily encourage you to consider the PASSdiy chassis currently available for pre-order until May 31st 2024. We also have a back panel parts kit to make life easier. Don’t forget the Keratherm.