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In Reply to: RE: Here is what you can do. posted by Michael Samra on July 14, 2016 at 23:30:47
The laptop should be a three prong plug. However one of the vintage pieces may be using a hot leg as ground?????
Any chance of reversing the plug and see if that helps?
Follow Ups:
All the tube stuff has been converted to three prong, but I understand where you are going with this, good suggestion. Some kind of ground loop is definitely a possibility.
old gear uses the ground AC line AS a ground. Even with the three prong plug it still may be reversed but you are not aware of it. if a different outlet worked out I would say this is your problem is reversed +/- line on your Sherwood.
Did you mean to write neutral? I thought that was a UL violation, even back then, but what the heck I can try it, not a big deal to swap them. I will let you know the results.
The old plugs didn't have a real hot/neg leg. You could put the old plug in any polarity. Besides how do you know if your outlet was wired correctly. I was an electrician and found MANY outlets wired in reverse. It made very little difference in the old days. Old stereos used the ground to the outlet AS the chassis ground. Hench hum issues when mixed with new gear.
Sounds like you got yourself the classic ground loop.
Play with the plugs.
charles
Sorry this took me a bit of time, with two pieces of equipment, preamp and amp, had 4 combinations, tried them all. There were combinations that added a bit of hum, no combination eliminated the beating switcher noise. Also checked the outlets, all wired ok. Didn't pop any breakers so none of the neutrals were tied to chassis. But thanks for the suggestion it was worth a shot.
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