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Power Amplifier project by Nelson Pass

Aleph J

The Aleph J is a single-ended, Class-A MOSFET power amplifier, with a Jfet driver stage.

Aleph J

Aleph J

From $ 25.00 USD
3 options

Key Information

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


  • Possibly the most popular Firstwatt for DIYers
  • It's an Aleph. "Everyone needs an Aleph" - Jim Tiemann

Links, Discussions & Files


This amplifier is a direct descendant of the legendary Pass Labs Aleph 3, the amplifier that turned the audio press upon it's ear, brought single-ended amps to many people, and catapulted Pass Labs into the forefront of specialist audio engineering and construction, where it still resides today.

Circuit description

The Aleph J is a single-ended, Class-A, MOSFET power amplifier, with a Jfet driver stage. It utilizes the Nelson Pass 'Aleph Current Source' to greatly increase the overall efficiency of the output stage, with the benefits of more linearity, a higher damping factor, and greater stability into tough speaker loads, doing all this with less negative feedback than it's predecessors. The Aleph J is a regular kind of amp - a voltage source amplifier, requiring nothing out of the ordinary from the preamp or the speakers.

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.