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Power Supply Hum

post #1 of 6
Thread Starter 
Hey Guys

Just finished building a new CMoy amp with buffered outputs. I'm powering the amp off of a regulated mains adaptor which is dishing out 24DC at 300mA. I'd been testing the amp for a while and everything was running sweet until eventually an annoying loud hum kicked in!

I'd narrowed the problem down to the power supply since using batteries eliminates the problem entirely. The strange thing is that the hum is intermittent, sometimes the hum is gone entirely and then itll just kick in and annoy the crap outta ya! Anyways, when playing music the hum also seems to dissapear, its not that the music is masking the hum, the hum itself stops.

I mean the supply is regulated so I shouldn't be having this problem right? One more thing, the input jack for the power supply connector has 3 tags. I've only used two of them, one for -ve and the other for +ve. Could it be that the third tag has some significance here?!

I'd seriously appreciate any help since I'd desperately like to get down to some serious headphone listening with this new beast without having to power it off a crappy 9V PP3!!

Cheers Guys,
Div
post #2 of 6
Thread Starter 
One more thing, several times now the LED on the amp has even flickered as a result of the hum stopping and starting again.
post #3 of 6
sounds like one of two things
1-cold solder joint,double check all of them,reflow all if need be
2-bad filter capacitor
post #4 of 6
Thread Starter 
On further listening playing music does not stop the hum, it simply masks it. I was wroing before. I also tried using another adaptor supply, and it gives the exact same problem! However, once again batteries eliminates the problem altogether. Man, whats going on?!

Rick, did I need a filter cap?? I mean I'm using a 24V DC regulated supply rated at 400mA. I've checked the joints and it all looks good, besides it couldn't be a joint since using a 9V PP3 sorts things out perfectly. I'm using a virtual ground driver with two paralled BUF634s, a single OPA637 per channel and two paralleled BUF634s per channel, if thats nay help.

Cheers.
post #5 of 6
would it be possible to post a schematic ? There could be many reasons for your problem but sounds a lot like a ground loop other than the flickering LED which sounds like oscillation.Do any of the parts feel hot ?Are you using a star ground ? double checked the false ground buffer wiring ? Double checked filter capacitor polarities ?
post #6 of 6
Thread Starter 
Rick, yes the BUF634s run quite hot actually. Only the ones in the output of the amp, not those in the virtual ground driver however.
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