bypassing diodes with caps

Ritchie · 1492

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Offline Ritchie

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on: December 02, 2013, 03:55:33 AM
Can anyone tell me if it is worthwhile to bypass power supply diodes with capacitors to supress switching noise?

Thanks

Ritchie M.

crack/speedball as preamp,linn lp12 w/radikal/keel/urika phono, linn majik 4100 active monoblocks,linn majik isobarik speakers(active).

Offline mcandmar

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Reply #1 on: December 02, 2013, 04:43:23 AM
I scrapped a few old amps for parts and found some of them had four small green poly caps ~.1uf directly on the bridge rectifier pins.  I asked about it on one of the DIY audio sites and the general consensus was that it can cause more problems than it fixes so dont bother.  In those cases we were dealing with the classic square bridge rectifier block instead of individual diodes, so its possible they may have been noisier and required them.

M.McCandless

Offline Grainger49

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Reply #2 on: December 02, 2013, 04:47:52 AM
This is a "fix" for reverse recovery spikes.  Most diodes do not turn off immediately when they become reverse biased, they leak the opposite polarity then turn off.  One fix is the diodes that Bottlehead uses, the soft recovery diodes.  Another one is using Cree diodes which are costly and hard to find. 

A trick someone on the old board told me was to put one Cree diode in series with the positive lead coming from the bridge.  It stops the noise.

A choke in the power supply will pretty much eliminate the spikes too.


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