Cootcraig Public Blog

Firstwatt F2 Build Log

Recently Nelson Pass released the schematic for the Firstwatt F2. It’s a current amplifier that can be used to power single driver speakers (eg, single driver speakers, AKG K1000 and possibly other headphones).

Penultimate Zen is the sum of several incremental improvements

Zen Variations 2

Zen Variations 3

Zen Variations 4

The Penultimate Zen is the sum of several incremental improvements to the original Zen amplifier of 1994. Eight years just flies by, doesn’t it? These improvements are contained in parts 2 through 4 of the Zen Variations, and is likely the last version of this amp, although by no means the end of the variations on the theme of single stage amplification.

In part 2 we developed an improved active current source load for the single gain device which is at the heart of the amplifier. Originally designed for the Aleph amplifier series, this current source doubles the output current and significantly lowers the distortion of the circuit over the original constant current source. As the original Zen amplifier is limited in both power and fidelity, this is a welcome improvement.

The original Zen amp is also limited in its rejection of power supply noise, and benefits from having a quiet, stable power supply. In part 3 we discussed some possibilities for power supply regulation for this and other Zen amplifiers.

The final shortcoming we will address in the Penultimate Zen is the low input impedance. Depending on the version and the desired gain and distortion figures, the original Zen amp has an