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First Watt F4 Clone

Designed by Nelson Pass. Class A push-pull power amplifier with no feedback and no voltage gain, only current gain. 25W (for 8 Ohm speakers), 40W (for 4 Ohm speakers). 47 kOhm input, 0.2 Ohm output impedance. More details on First Watt website.


  • 4U Deluxe chassis (Hi-Fi 2000) with an extra hole on back panel for XLR socket

  • All boards from diyAudio Store

  • Matched MOSFETs from Hannes

  • Matched JFETs from FET Audio

  • 500VA transformers custom made by Avel Lindberg 2002 - 2x115V primary, 2x18V secondary

  • 8 x 22000uF in PSU

  • R1 changed to 100k 0.1% in preparation for ImPasse


  • Rails: +/- 25 VDC

  • DC Offset: < 1 mV (< 30 mV cold)

  • R3/R4: 60mV



Last update: 28.09.2014.

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