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First Watt M2 Clone

Designed by Nelson Pass. Class A push-pull power amplifier with no feedback and voltage gain created through an auto-former which magnetically multiplies the input voltage. 25W for 8 Ohm, 40W for 4 Ohm speakers. More details on First Watt website.

SCHEMATIC

MEASURES

  • Rails: +/- 24VDC under load

  • DC offset at speaker teminals: +/- 2mV

  • BIAS: 1.3A (0.61V on R13/R14)

  • Voltage gain: 10 (20dB)

  • THD+N (at 1 Watt into 8 Ohms at 1kHz): 0.08%

  • THD (at 1 Watt into 8 Ohms at 1kHz): 0.04%

NOTES

  • R7 changed to 52.3k to remove excess negative DC offset at the output of the amp

  • R4 changed to 8.2 Ohms and 220uF bipolar capacitor added to remove DC offset at Edcor input (pin 1)

  • Boards, Edcor transformers and MOSFETs from TeaBag

  • Harris IRFP9240 MOSFETs

  • Matched Toshiba JFETs from FET Audio

  • Dual mono implementation

  • 2 x 250VA transformers from Toroidy - 230V primary, 2x18V secondary

  • 8 x 22000uF KEMET PEH200 in power supply

  • Deluxe 4U chassis from Hi-Fi 2000

Last update: 10.03.2019.

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