Big film caps and noise

[SY]

The Pass amps are run open loop. Many have a high source impedance compared to the chip amps run closed loop. OK, do I still need to ask question 4?

 

[Conrad Hoffman]

xiphmont, you've really done it now- we're bound to see circuits containing unshielded grapefruits! (if they passed a law against putting tennis balls in toilets, half the toilets in the US would be plugged up within the hour)

Sy, I'm not familiar with the particular Pass amp in question, but having seen his design philosophy on various things, that's why I added the weasel words and caveats about damping and equalization. My guess is that there would be be an obviously audible difference if the two amps were just substituted plug-for-plug. I'm not in any way knocking that philosophy, just pointing out that the conditions for indistinguishability are rather well defined, and easily violated by the casual tester.

 

[KSTR]

The foil cap turns out to be coupling hum and hash noise coming from the PSU. Although shielding the input cap helps, eliminating it entirely or using an electrolytic yields

Just food for thought, and more or less off-topic: When you have that much hash from the PSU then I would attack the problem at the cause (the PSU).

- Klaus

 

[SY]

I'm not in any way knocking that philosophy, just pointing out that the conditions for indistinguishability are rather well defined, and easily violated by the casual tester.

1000% agreement. It's a point that I've made over and over. If two boxes of gain can be verifiably distinguished by ear, the explanation is never mysterious.