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.
NOTES
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4U Deluxe chassis (Hi-Fi 2000) with an extra hole on back panel for XLR socket
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All boards from diyAudio Store
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Matched MOSFETs from Hannes
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Matched JFETs from FET Audio
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500VA transformers custom made by Avel Lindberg 2002 - 2x115V primary, 2x18V secondary
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8 x 22000uF in PSU
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R1 changed to 100k 0.1% in preparation for ImPasse
MEASURES
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Rails: +/- 25 VDC
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DC Offset: < 1 mV (< 30 mV cold)
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R3/R4: 60mV
SCHEMATICS
RESOURCES
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Service Manual: First Watt F4
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diyAudio: F4 power amplifier, F4 guide, Store
Last update: 28.09.2014.