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Intro:
In Part 2 we developed a new active current
source for the Zen amplifier. In this part, we create a power supply regulator suitable for the Zen
amplifier projects.
Previous versions of the Zen amplifiers had no
power supply regulation at all, or used capacitor/inductor/capacitor "pi" filters to smooth
the ripple on the DC supply lines. In keeping with our philosophy of simple-as-possible, we want to
develop a supply regulation system which gives us good regulation, with low AC noise and a stable DC
value.
The need for a good regulator is obvious enough.
As simple as they are, the Zen amplifiers do not have particularly great power supply rejection ratios
(PSRR), the measure of how much of the power supply variations bleeds into the signal path. In the
original Zen amplifier, ripple voltages of 1 volt or so typically caused 2 milliVolts or more of the
same noise on the output of the amplifier. In this case the PSRR is about 500 to 1, or about –54 dB.
2 milliVolts might seem sufficiently low, that is until you hook the amp up to a 110 dB sensitive horn
midrange, and then you will start looking for less noise.
You can make the PSRR of the amplifier higher,
or you can clean up the supply. A "pi" filter will take out most of the ripple, but will not
stabilize the value of the DC against fluctuations in AC line voltage. For this you need an active
regulator.
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