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Introduction
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 input impedance that varies from 600 ohms to a couple
thousand ohms. For many audio sources, this input impedance is simply too low to give optimal
performance. The ideal input impedance would be something up around 47 K ohms.
We will address this fault here and now, and
then go on to present a final circuit with a nice finished printed circuit board design.
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