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RE: Motor Run Caps for the BB Proof Amp

I few things have come up in this thread ...

* The revised circuit uses two electrolytics in series for the first power supply cap, only to obtain a voltage margin for better longevity.

* Film caps also have a much longer lifetime when operated below their max rated voltage. This is mildly true for polypropylene and strongly so for polyester films.

* The DC rating for capacitors is sometimes much less than 1.4 times the AC rating; many AC caps do not handle DC very well. Like facebook says, "it's complicated". Check the ratings, read the data sheet! If the manufacturer won't rate it for DC, I would not use it for DC.

* The revised circuit has resistors across those caps to bleed them down when the amp is off - there should have been such a resistance in the first diagram as well.

* The power supply filtering is (by my calculation) the minimum required to get the power supply hum at or below the residual from the AC filament power. Since this is a calculation, not a measurement or listening test, I can't yet say the caps are the right value for best performance. Keep that in mind before investing heavily in pricey caps!

* I simulated the power supply in PSUD-2 to check the peak rectifier current and confirm that it is below the rated maximum with 50uF as the first cap. This is because we are drawing only 60mA; if we were drawing the full 175mA max rated current for the 5V4 then 50uF would be far too big a capacitor.

I have deliberately put up a best-guess design, inviting and counting on the hive-mind of the forum to test and improve it. I'm trying for more consensus, less guru/ego design.

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