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Author Topic: Separate power supply filter for each channel - why?  (Read 422 times)

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Separate power supply filter for each channel - why?
« on: September 08, 2019, 04:16:41 PM »
The subject line says it all. I've been wondering about this for a while.

Does it have something to do with the last cap being in the signal path? In which case, separate filters for each channel provide some noise/crosstalk isolation between channels?

But if that's the case, why doesn't the Kaiju have dual power supply filters?

cheers and thanks, Derek

Offline Paul Birkeland

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Re: Separate power supply filter for each channel - why?
« Reply #1 on: September 08, 2019, 05:27:41 PM »
[email][email][email][email][email]The parafeed cap is the dominant cap in the signal path.  The issue you run into is getting the power supply quiet enough without dropping too much voltage and without cooking off a ton of heat.  For the original Stereomour, there were a bunch of 5W and 10W resistors on a PC board, and we either would've wound up with too much voltage loss or not enough noise reduction with a single supply per amp.  In the Stereomour II, the availability of the DC filament supply meant that the B+ supply needed to be even quieter, so we split the resistive part of the old power supply into two resistors.  Since we were replacing the power supply PC board with a DC filament PC board, it sure was handy to work with 3W resistors in the power supply instead of higher power/larger parts.  An alternative would've been a more dramatic power transformer redesign to bump up the B+ to allow for a shared supply. 

The Kaiju is a physically larger amp that's far more able to fit 10W resistors and to handle the heat they put off.  It also wouldn't be all that great with 450V power supply capacitors, so we have caps in series to provide lots of voltage overhead.  The power supply in the Kaiju takes up a ton of space so it was sensible to stick with a single supply for both channels.  You'll also notice that the Kaiju and Stereomour power supplies are both CRCRC with approximately the same R and C values, which makes for consistent noise floor performance. 

If the Kaiju was in an 18" x 12" chassis, we might've gone with dual mono power supplies, but as it is the Kaiju is a rather large amp.
Paul "PB" Birkeland

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Re: Separate power supply filter for each channel - why?
« Reply #2 on: September 08, 2019, 06:08:39 PM »
Many thanks PB. I think I see what you mean.  Splitting the current draw between two filters decreases ripple and pumps up the voltage.  That's a neat trick.

cheers, Derek