Pass Labs First Watt F5

f those requirements. Single-ended Class A, the Aleph J is an easy-going design which is happy driving 8 ohm loads with a warm, relaxed presentation. By way of contrast, I present the F5 (taa-daa!), a push-pull Class A amplifier, utilizing JFETs and MOSFETs in a very simple two stage complementary circuit a little bit like a complementary version of the Aleph J. But like all the
other First Watt amps so far this one is different.
In many ways, it's an ordinary topology - the basic circuit is found in numerous preamp circuits and the odd power amplifier (Check out the Profet amp from Selectronics). But the F5 is the product of numerous decisions that set it apart.

In many ways, it's an ordinary topology - the basic circuit is found in numerous preamp circuits and the odd power amplifier (Check out the Profet amp from Selectronics). But the F5 is the product of numerous decisions that set it apart.
It has very wide bandwidth, DC to > 500 KHz.
No capacitors anywhere in the circuit. (except in the power supply, of course!)
It has a high input impedance 100 Kohms, and a high damping factor (~60)
The distortion is very low, between .001% and .005% at 1 watt.
It's very quiet, about 60 microvolts or so.
It will drive a 2 ohm load without burping, and 1 ohm without misbehaving.

Previous Next

Klik op de afbeelding voor een vergroting
Click picture for magnification

Measured at 120 V AC with a 25 ohm source and an 8 ohm load:
Distortion @ 1 watt .001% to .005% @ 1 KHz
Input Impedance 101 Kohm
Damping Factor 60
Output power stereo 8 ohms 25 watts @ 1% THD, 1KHz
Voltage Gain 15.3 dB
Maximum unclipped output +/-20 Volts
Maximum output current 10 amps
Frequency response - .0 dB @ DC, -3 dB @ - 1 megaHertz
Noise -60 uV unweighted, 20-20 KHz
Power consumption 180 watts
Fuse 3AG slow blow type, 2.5 Amp for 120VAC
1.25 Amp for 240 VAC