Amp Hum

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.

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.

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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The suggestion of a faulty ground seems a likely possibility. With everthing unplugged except the amp, ground the amp from the ground of one of the RCA plugs to ground at the outlet. I had a Rowland 5 that had this problem. It was just a loose wire on the input of the IEC connector for ground. It also got worse over the first 20 seconds or so of warm up. I was rather surprised that the hum was so bad since the unit was effectively grounded through the interconnects and other equipment--but it was.

Definately call B&K they are more than happy to advise you on potential problems or even suggest a fix. They are only in NY and a pleasure to deal with. A hum that is isolated to the component can be two things... faulty ground or
bad or noisy transformer or power supply...
take the piece over a friends and plug it in... see what happens and if hum still persists.. call B&K.
Good Luck!
Joe

Can you hear the hum from the listening position or when you put your ear to the unit. If the latter is true this is normal. Steve

If everything is disconnected and you hear a hum from this unit, I beleive you may have a transformer hum. (a noisy transformer) In this case, it would be wise to discuss this with the amplifier manufacturer. cordially, Richard..

Is the factory cord actually grounded i.e. a three pin connector ? If it isn't, you might have the polarity reversed on the plug or the outlet. This can introduce a hum into the amp which is then fed through the speakers. Sean
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