A-75 buzz

I am a rookie.

But somehow I managed to build an A-75 about 2 years ago and since then I have lived with a buzzing sound, not too annoying with my main speakers but really obnoxious with some single driver boxes I am now toying with.

Question: The buzz is not the traditional hum, but more like what I would suspect is related to either the diodes or voltage doubler circuit in the regulated power supply. Where should I look for the source and/or how can I eliminate (or reduce) the buzz?


Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Look on the rails for the front end using a scope,
and if they look like they don't have any ripple,
say only a few millivolts AC, then the amplifier
might be oscillating, in which case you look for high
frequency noise at the output, again using an
Did you add the bypass electrolytics to the driver card board? There was some slight oscillations that showed up on a few of these that were eliminated by placing an electrolytic from the + , - power inputs to ground on the driver cards. I think 150 mf, polarized. Keep - pointing to - and + pointing to + . This will mean where they come together at the ground you'll have a - to a + .