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Ground Cheater plug or....

Maybe this isn't a good idea, but I thought I'd ask anyway.

I have what I believe to be a persistent ground loop hum from my amplifier. It's quiet, inaudible if music playing or unless you're standing next to the speaker, but knowing it's there is annoying.

I've heard suggestions to use a cheater plug to defeat the ground, but it seems counterintuitive to stick a 35cent plastic plug between expensive cables and power supplies. My question is, couldn't you accomplish the same thing by disconnecting the ground wire in the outlet, and still exact the benefits of better cables?

I'm sure the fire marshall would disapprove, but I'd like to hear what the hi-fi nuts have to say.

Cheers!
grimace
jea48
2,944 posts
 
Grimace,

When you sent the amp to Cary did you also send along the power cord that is used on the amp?

How about the repair shop. Did you take the power cord with the amp?
>>>>>>>>>>>

I assume you have a multimeter.

(1) With the amp turned on measure the AC voltage at the wall duplex receptacle.

(2) With nothing plugged into the duplex receptacle measure the AC voltage.

(3) Check the AC voltage from the hot contact to the equipment ground contact.

(4) Check for AC voltage from the neutral contact to the equipment ground contact...
Make sure the meter is set to AC auto.
Make sure both meter test probes are making good contact.

Post back the measurements.
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puerto
372 posts
 
I use cheaters on my mono blocks to solve the same issues - nothing else worked!
broimp
10 posts
 
I had the same problem. Cause was the fact that one of my amps uses a grounded plug, the other not and they live on the same circuit, unfortunately. You may want to look to see if you have a similar situation. Two and 3 prong devices on the same circuit can cause this problem. Start disconnecting and reconnecting stuff and you will probably find out what is doing it. Chances are nothing is broken. I wound up using a cheater. No fires so far (10 years)
broimp
10 posts
 
Yes all devices you have are grounded, some are chassis grounds (2 prong devices) and some externally(3 prong). The problem is that these grounds are just different enough to create a small current flow when they are on the same circuit and that is what you hear as 60 Hz hum. Rewiring all to be 3 prong will most likely fix, but that is pretty extreme. Not saying this is your issue, just that it was mine.
grimace OP
624 posts
 
So here's what fixed it. I switched pre-amps, and suddenly the amp was quiet, but when I turned on the pre-amp the hum came back. It had mysteriously jumped between components! To finally get it to settle down, I stuck a cheater plug between the pre-amp and the power supply - the PS is still grounded at the wall - and that fixed it. I don't hear any sonic degradation from the cheater. Cheaters seem to be controversial, but at this point, and since the PS is still grounded, I'm not arguing. But hell's bells. it took a year to figure out.
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