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Ground loop hum - Can one amp be much more sensitive to this?


psg

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Some of you may recall a hiss problem I had last year using an amp I had on load. I finally couldn't stand it and pulled it out of the system. When I got my Tuba HT sub build in December, I pulled it out again to power the sub since hiss wouldn't be a problem on a sub. It has a ground loop hum.

I disconnected every input and monitor output from my receiver and the hum was gone. It turns out that I am getting hum in the sub by plugging any RCA-based or HDMI connector to the TV screen (which is at the other end of the room on a different electrical circuit), or any RCA-based or HDMI connector to the satelite receiver. I connected the ground screw of the power amp to a ground pin of an outlet on the TV electrical circuit and the hum must have dropped by 10 dB. But it's still audible and distracting.

So, as a further check, I pulled out my old hk avr-325 receiver, connected the sub to a main channel, calibrated the volume level on the receiver to get the same output as with theproblematic external amp, and... no hum. Dead quiet.

My question is: is it normal that an amp would be prone to ground loop hum while another would not be? How do I check for this when I buy a power amp for the sub? Roll of the dice? I was thinking maybe a Behringer EPQ1200 (enough power, RCA inputs, several output power LED indicators).

Thanks!

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Downside (I think) is you risk the chassis of the amp being 'hot' (as in electrically charged?)

I think I read one way around this was to plug the amp into a GFCI outlet and the GFCI would offer some protection that the ground prong is currently offering.

I don't know if the above is accurate so perhaps others will chime in.

Seem that cheater plug use can be an intersting topic of conversation. You DID say it was a cryo-treated cheater plug right? So it's audiophile grade.

[;)]

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What's the safety downside, if any (since not all electrical appliances have three-pong plugs anyway)?

It could make it a shockingly good amp, what's a little 115V between friends?

I would do it. Now you may not want to run out the shower dripping and touch it . [li]

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It could be the satellite system. Very common issue. Unplug the satellite box and see what happens. I run my satellite box with a cheater plug so it can't introduce another ground. Another thing to try is to just unscrew the incoming coax to eliminate that as a potential issue.

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OK, now the safety aspects. You know that potentially touching something ungrounded, and anything else could pose an issue. Just be careful.

I run every single piece of equipment I own on a cheater plug and use GFI outlets. Still, 2 separate Behringer 2496DCX processors that I owned electrocuted me (very minor shock in those instances)........when I touched the Behringer and another piece of equipment. No GFI tripped.

So be careful. It could be worse.

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If I have an elctronic unit that causes hum when plugged in and the hum is removed by using a two prong adapter I get rid of the improperly designed unit. That means they scimped to save money on the power supply and you eventually will have problems. My opinion base on 40 years experience so please don't get mad.

JJK

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OK, now the safety aspects. You know that potentially touching something ungrounded, and anything else could pose an issue. Just be careful.

Correct me if I'm wrong but if you have a hum caused by a ground loop, it is because you have two or more ground paths. As long as all the equipment is plugged in together, you still have a ground, no? The risk is if you un-ground, the system unknowingly and have no ground remaining.

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The risk is if you un-ground, the system unknowingly and have no ground remaining.

I don't know that cheater plugs "unground" the system -- aren't both amps grounded through the "neutral" blades of the power cords? Remember, the 3rd, or "grounding" pins, end up going to the same place as the "neutral" in many electrical panels. The cheater only lifts the grounding pin, not the neutral.

In my case with 2 ML-2's, somehow, there was a ground loop between those various pathways (2 per amp) to the single ground for the entire house. It didn't seem to have much to do with the other grounding pathways for the preamp and sound sources via a variety of interconnect "grounds."

JJ: That means they scimped to save money on the power supply and you eventually will have problems.

Well...a pair of ML-2's cost many thousands of dollars in the 1970's and showed it when you looked inside (70 lbs. each!). Wouldn't it have been a philosophical circuit design issue?

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I fought a similar issue for some time before finding the solution.

I used to have a Yamaha 795A 5.1 receiver. I also had a Bryston 2BLP stereo power amp and a Anthem MCA-20.

I wanted to use the Bryston for the L/R mains, being a better amp than then Yamaha. Use the Yamaha for the center and surrounds and the Anthem for my subs.

No matter what I did the Bryston would hum badly. The Yamaha would not hum nor the Anthem.

I finally determined that the cable coax coming into my house and the 120V neutral were at different ground potentials and what was causing the problem.

I tried a cheaper RS filter which didn't work. The addition of a $50 Jensen isolation filter fixed all!

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If you lift the chassis ground the chassis floats "somewhere", at some minimal voltage above ground. An electrical issue iside the unit could make it hot or somewhat hot (some minimal voltage). This is the danger. You touch 2 things of different potential and you get a shock. The cheater plug ungrounds the chassis.

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This is off topic but you all might get a jolt out of it... I know I did.

Was at father in laws house. He needed a new element put into his water heater. This was a comedy of errors.

I learned that you can replace a heating element very quickly if you don't mind some blurbs of water spilling out. You will not however, lose the tanks contents since air has to go into the same hole (water is of course, turned off)

So, here I sat... power turned off, water turned off. I pulled out his heating element.... and OMG... the replacement was still in its hermatically sealed wrapper. Stupid me forgot to open it. So now I'm sitting here, one hand trying to hold the original element in the hole while with my other hand and teeth, rip open the replacement element.

Long story short, I ended up sitting in a mild 'puddle' of water and.... was receiving a noticable shock as I'd grab the heater parts.

It wasn't a full 110 volt (nor 220 thankfully) but it was enough to 'bite' at your fingertips. The breaker was turned off but, now I'm fearing something is cross wired somewhere and I'm still getting some juice... so I tell them to kill power to the entire house.

The entire house now goes dark and I'm sitting in a closet with a dull flashlight....

STILL getting shocked when I touch this thing. [:|]

Now I'm baffled.... I'm not comforted with the fact that I'm sitting in a puddle of water getting slowly cooked with electricity. We called my wifes brother (electrician) and I don't remember his comment but it was basically to get out of the water (duh) and call the power company.

Cutting to the chase, it seems one of the power lines near us (in the woods so invisible to us) had severed and was shorting to the ground. This was allowing the current to go either through my butt to my fingertips and back to the power company or the other way around.... I don't know.

Either way, the power company came out PROMPTLY the next day, surveyed the lines and discovered the problem. they shut it down and fixed it right away.

It was a weird sensation getting mildly shocked while working on something knowing that power to the entire house was killed.

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Fantastic story Coytee!

As for me, I did connect a ground connector on the back of the power amp to the ground pin of the TV screen outlet, so even if the ground pin was lifted from the amp's power cord, the chassis was grounded... somewhere. Still, I suppose hum means there is some potential for voltage difference there to shock you.

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