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RE: SET Power supply in series with output trans

"I speculate that frequency response is not the right criterion. My tentative candidate is envelope modulation - that is, the fluctuations in musical loudness. This is clearly dependent on the music as well as the amp time constants, which does muddy the waters."

One needs to distinguish between class A and class AB amplifiers here. In class A, the average current draw from the power supply is essentially independent of the loudness of the music. The fluctuations in the current draw are on the timescale set by the audio frequencies in the musical signal. Essentially, the job of the final smoothing capacitor is to hold the supply voltage nearly constant during the period of the lowest frequencies that one wants the amplifier to reproduce without colouration. (Bypassed by smaller capacitors too, if the main capacitor has higher-frequency deficiencies.)

By contrast, in a class AB amplifier the average current draw from the power supply can increase very substantially when the music gets louder. In this case, sagging in the power supply voltage during extended loud passages could certainly be a problem in the case of a poorly designed power supply. It seems to me that it is in these class AB cases that the envelope modulation you are alluding to would be a problem.

Of course, if one actually wants a colouration in the sound of a class A amplifier, such as a low-frequency fall off, then a less than "ideal" power supply might give a more pleasing sound. But this, or any other colouration of the sound, might be better achieved in a more controllable fashion, using purpose built audio filters.

Chris


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