Classic Hifi Care

Decided to play some music today and kick back after yesterday's festivities ... My aircraft carrier sized maggie always had a slight hum in the background nothing to noticeable... imagine a guitar amp turned up without a guitar plugged in... that is the type of hum it has .. I went though the amp and the power supply completely with all new high quality caps , and the hum never changed ... today it got noticeably louder.... There is AC ripple leaking in somewhere in the amp... we have a few LED light bulbs and when I turn one on the buzzing got even louder. I wouldn't think LED's would have a effect on a transformer supplied power supply ?... a switching power supply I would expect the noise... I think the first step is to pull the chassis and measure AC across the caps while under power...maybe one of the new caps was defective ?
Elton

Or one is wired backwards? Sounds like you are on the right track. Good luck.

Edit.....I've been thinking about this a lot for some reason. We know you don't have a heater to cathode short, since there are no heaters and no cathodes. We know you don't have defective cathode bypass components, since you have no such components. Assuming the hum is there in all modes, one could logically eliminate a short to ground in an input connection. So about all that leaves is a capacitor somewhere not doing its job. Either it's defective, of too low a capacitance or it is installed backwards. One would think that if it was installed backwards, there would be more obvious issues, like smoke or something like that. One could check for AC after the rectifier and filters where it should not be. Solid state devices don't have high voltage past the rectifier. That chassis probably runs on 12 or 16 VDC instead of the 350VDC we see in tube chassis. Perhaps a filter cap is under capacity. You could bridge the filter caps with known good electrolytics of equal or greater capacity and see what you get. If the hum has gotten worse recently, that lends more credibility to the defective cap theory. Tinker with it a bit and let us know what you find. Good luck.

so lying on the floor behind the behemoth looking at the wiring , I had a DUH moment ...the input from the tuner chassis easily unplugs from the amplifier, so I plugged a mp3 player directly into the amp input , and lo and behold no hum in the speakers ... so the fault lies somewhere in the tuner chassis itself...so forgetting the first basics of troubleshooting... inject a signal ... the older i get the dumber I get...

I'm sure you guys all know this, but I was surprised. My Zenith had a slight hum that would get louder when I touched the tonearm. Unplugged the console, turned the plug around and plugged it back in. The hum was gone! On this unit at least, the polarity made a difference.

My Maggie Symphony has a hum when I touch the tone arm. No sure why, and have not bothered to check it out. When I got it, the cartridge was hanging out of it and someone had hacked the wiring leading up to it. I think the first thing I should do is install new wires to the cartridge. The other thing, and I'm guessing here, it's either the wrong cartridge, or, it's mounted wrong. It does not track correctly, like it's not sitting down in the grove far enough. It sounds terrible. The radio plays great, and I have tired another changer and that plays great too.

Bill

I can see reversing the plug making a difference in hum on a hot-chassis set. One with a power transformer, not so much. The power transformer should isolate the chassis from the line, hence should kill the hum.

Bill, wonder if that could be a ground issue with the changer?

That's kind of what I'm thinking. The way someone hacked the wires that go from the under side of the changer to the cartridge was horrible. When I get back to it, I will change out those wires and see what I have.

Bill

Since reversing the plug got rid of the hum on my Zenith, is that then indicative of something else wrong, like a bad ground?