Memory Distortion - Part 7 : Power Supplies

The effect of power supplies on sound quality has been known for a long time. In power amps, feedback is supposed to reject everything that happens on the power supply lines (the famous power supply rejection ratio).

The case of power amps is interesting, because most of them use unregulated power supplies. Therefore, when the amp needs to put out a lot of juice (on a transient, or when it clips), rail voltages will sag a little. How much will depend on the "stiffness" of the power supply (capacitor size), and wether or not the rectifying diodes are conducting when this current demand happens (in which case the current will come directly from the transformer).

Of course, moving rail voltages will not only affect dissipated power in devices, but also shift the operating parameters which depend on supply voltage. I tried to run some simulations with very pessimistic power supply sag (1 volt during 1 second), and I found that the memory effect is measurable, around 0.8 units in the scale we previously used, for the standard amplifier configuration. The New amplifier configuration that was examined in the last chapters shows no measurable memory.

So, here is yet another reason for regulating the power supplies in the signal stages. Dejan has been knowing that for what, 20 years ?.....

The Kick ass amp will, therefore, have two power supplies, one for the signal stages (fully regulated), and one for the output stage (unregulated, but with biiig caps).

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