Pass Labs First Watt F8 Power Amplifier

Pass Labs First Watt F8 Power Amplifier


Originally created almost 6 years ago, the F8 is a stereo two-stage single-ended Class A amplifier using the NOS Toshiba 2SJ74 P channel Jfets and SemiSouth R100 SiC power Jfets for signal gain, plus IRFP240 Mosfet mu-follower current sources, for a total of three devices per channel.

It is similar to the J2 amplifier, but has only one front end transistor instead of six, operated as a current feedback amplifier (CFA) as opposed to the J2's voltage feedback (VFA) differential input. This front end is more consistent with the single-ended approach to amplifier design and yields a purer second harmonic character, less distortion with lower negative feedback, greater bandwidth and higher damping factor.


Distortion @ 1 watt, 8 ohms 0.015%
Input Impedance 100 Kohm
Gain 15 dB
Input Sensitivity (1 watt) 0.53 V
Input Sensitivity (max output) 2.6 V
Damping Factor 40 @ 8 OHMS
Output power 8 ohms 25 watts @ 1% THD, 1KHz
Output power 4 ohms 15 watts @ 1% THD, 1KHz
Frequency response -0.5 dB @ 10 Hz, 200 KHz
Noise <100 uV unweighted, 20-20 KHz
Power consumption 170 watts
3AG slow blow type -
2.5 Amp for 120VAC
1.25 Amp for 240 VAC