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Amp Hum

I've got a B&K AV5000 Series II amp with a hum. It gradually builds up over about a 5 second period on startup. I've disconnected everything (preamp, speaker cables) and still the hum persists. I tried a different power cord (Shunyata Sidewinder), made sure everything else was off, tried a cheater plug, different wall socket... still have the hum. I tried the Monidal Magic thing for the cable, still the hum torments me. Is it time to take it in or am I missing something? Thanks-
scrapiron
sean
6,231 posts
 
This could be a lot simpler than i thought. I've run into this on other amps, including B&K. Pull the lid and check to see if the toroidal transformer is tightened down. I have seen where these were not snugged down properly at the factory and have vibrated loose in transit or over time. I would suggest unplugging the unit from the wall first though while leaving the amp on. Let it sit for a few minutes and then make sure that it is snug using the proper tools. Sean
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bufus
149 posts
 
Sean has a good idea. My Adcom hums and I talked to a dealer about it. He told me to open it up and make sure the transformer was tightend down good. I have never bothered doing it beacuse I can't hear it from my listening position. Yes, be careful to make sure you unplug the unit and leave it sitting for a good long while so that the caps discharge. I would let it sit overnight. I'm extra cautious.
mdomnick
332 posts
 
I was rewiring my gear last night and heard a hum coming from my mid-range driver. I was used to this but surprised how loud it had gotten, and it usually went away...presumably after some parts warmed up (especially the tubes) but this time it stayed. Long story short, I found several loose screws holding key parts in place, tightened them, and the hum went away. I'm afraid to turn the amp off in fear of the hum coming back, but as of now the speakers are dead quiet.
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