Ground Loop Hum

[slipperybidness]

OK guys, I got a new amp recently, hooked it up, and it had an obvious hum. Quick-fix to check out the amp and troubleshoot, I just got one of those 3prong to 2prong adapters to defeat the ground. Problem solved, temporarily.

In general, I would prefer to not defeat the ground, especially on something that can deliver this much power.

I played around with it some more, and I noticed that my pioneer elite reciever (used as pro) is not grounded at all, only a 2prong plug. To add to this, the pioneer has a "ground" connection on the back for a turntable. I guess there is an internal "ground" for the pioneer?

Any ideas on how to solve this problem and why the pioneer would only be a 2 prong plug?

 

[walter duque]

In general, I would prefer to not defeat the ground, especially on something that can deliver this much power.

I wouldn't worry about putting out that much power. I use a cheater plug on my amp that puts out 350 watts X 6 watts into 8 ohms and 500 watts X 6 in to 4 ohms for the last 14 years and never had a problem. Just as a note, I ubuse my amp. Sometimes that's all it takes, is a 99 cent plug to solve the problem.

 

[slipperybidness]

OK, I've been doing more troubleshooting and trying to resolve this issue without resorting to a cheater plug, but no luck.

I'm now thinking about using a cheater to defeat the ground, but using one of those GFCI plugs designed for power tools. So, I would have the GFCI plugged to my grounded recepticle, a cheater plugged into that to defeat the ground from the amp, and the amp plugged to the cheater.

Will this give me any protection from shocks? As good as an actual ground? Any problems with this approach?

 

[agarwalro]

First try and determine which device is causing the loop and then simply remove ground on it. To find the offending device, turn everything off and then start unplugging equipment till the hum is gone.

 

[Rickster71]

Is the pre/pro hooked to a cable box? If so, try disconnecting the cable box from the rest of your system.

If not, run a ground wire between the Amp and pre-amp cases/frames and get rid of the cheater plug.
Plug everything into the same outlet or power strip.

 

[highfigh]

OK guys, I got a new amp recently, hooked it up, and it had an obvious hum. Quick-fix to check out the amp and troubleshoot, I just got one of those 3prong to 2prong adapters to defeat the ground. Problem solved, temporarily.

In general, I would prefer to not defeat the ground, especially on something that can deliver this much power.

I played around with it some more, and I noticed that my pioneer elite reciever (used as pro) is not grounded at all, only a 2prong plug. To add to this, the pioneer has a "ground" connection on the back for a turntable. I guess there is an internal "ground" for the pioneer?

Any ideas on how to solve this problem and why the pioneer would only be a 2 prong plug?

The power output has nothing to do with the grounding pin. The receiver or, if not using a receiver, the preamp is the piece that generally has the grounding pin. Some power amps have it, but some of those will have a ground lift switch to disconnect Pin 1 of the XLR.

As Rickster posted, if you have cable TV, disconnect the cable feed and find out if the hum goes away. There's a great chance that the hum will. If it does, you can either use a de-coupling adapter on the cable feed or you can have the cable company ground the cable at the entrance to the building. The grounding of communications service entrance is covered in the National Electrical Code.

 

[highfigh]

OK, I've been doing more troubleshooting and trying to resolve this issue without resorting to a cheater plug, but no luck.

I'm now thinking about using a cheater to defeat the ground, but using one of those GFCI plugs designed for power tools. So, I would have the GFCI plugged to my grounded recepticle, a cheater plugged into that to defeat the ground from the amp, and the amp plugged to the cheater.

Will this give me any protection from shocks? As good as an actual ground? Any problems with this approach?

As good as an actual ground? If you lift the ground, you won't have one and therefore, you won't be protected. Neither will the equipment. Do it right- fix the problem, don't use a band-aid.

What do you expect the GFCI to do for you? That's not a ground-lift device- it senses connection between the hot and neutral legs.

 

[bikdav]

Suggestion

If all else fails, try one of these from your nearest Radio Shack store. It has massively reduced _ if not completely eliminated _ my hum problems without fail.

 

[slipperybidness]

The problem manifests through the ground on the amp. This happens when ONLY THE AMP is plugged in even. If I lift the amp ground, then the hum dissappears.

I have tried unplugging every piece of equip, still the hum. My reciever does not have a ground pin at all, only the amp.

 

[slipperybidness]

Is the pre/pro hooked to a cable box? If so, try disconnecting the cable box from the rest of your system.

If not, run a ground wire between the Amp and pre-amp cases/frames and get rid of the cheater plug.
Plug everything into the same outlet or power strip.

Yeah, I could run a ground b/w reciever and amp, but the reciever does not have a ground pin so this is pointless.

 

[slipperybidness]

As good as an actual ground? If you lift the ground, you won't have one and therefore, you won't be protected. Neither will the equipment. Do it right- fix the problem, don't use a band-aid.

What do you expect the GFCI to do for you? That's not a ground-lift device- it senses connection between the hot and neutral legs.

I hoped that the GFCI would offer some shock protection, that is all. I realize it is not a ground lift, I can lift the ground with a cheater.

 

[Rickster71]

I have tried unplugging every piece of equip, still the hum. My reciever does not have a ground pin at all, only the amp.

Just so I understand fully.
Are you also unplugging all the RCA connectors to the amp?
For the test, the only connections are: the amp is plugged into the outlet and amp to speakers. Do you still get a hum in the speakers?
If so, have a repair shop check the amp.

 

[Rickster71]

Yeah, I could run a ground b/w reciever and amp, but the reciever does not have a ground pin so this is pointless.

That is exactly why you would want to tie the amp and preamp together with chassis grounds.
The ground pin on the amp and the neutral blade on the preamp are offering to different ground potentials.

 

[highfigh]

The problem manifests through the ground on the amp. This happens when ONLY THE AMP is plugged in even. If I lift the amp ground, then the hum dissappears.

I have tried unplugging every piece of equip, still the hum. My reciever does not have a ground pin at all, only the amp.

So you're saying that if no input cables are plugged into the amp- it still hums? No input or other connection to any other equipment, other than the speakers?

 

[ratso]

well here we go again. having wrestled with ground loops, please do yourself a favor and go to the experts. there is more misinformation about this than anything else i can think of in this hobby.

http://jensentransformers.com/an/ts_guide.pdf

contact them before buying anything, they can help.

 

[ratso]

btw please note the part that says "DON’T CREATE A LETHAL SHOCK HAZARD" and then shows a cheater plug.

 

[highfigh]

I hoped that the GFCI would offer some shock protection, that is all. I realize it is not a ground lift, I can lift the ground with a cheater.

A GFCI is made for safety- definitely, but ONLY if the circuit is wired correctly and the equipment is un-modified and the fact that you have hum means there's a difference in potential between the two pieces. "Difference in potential" means that if you connect a voltmeter to each piece, you will measure voltage between them. If you lift the ground, it's possible that the chassis of that piece will become "hot", meaning that the full line voltage will be present if you measured from it to a good ground. This is why power cords of many items now have a three-prong cord- the chance of being electrocuted was high if a person touched the chassis (or something else that was connected to it) of one piece and another piece that was grounded or wired for reverse polarity. Guitar amps had a 'ground' switch for reversing the polarity and the recommended way to find out if it needed to be flipped was the amount of hum when it was near another piece of equipment. Touching the guitar strings (or anything that was connected to the cable's shield) and another amp, guitar or a properly grounded mic sometimes resulted in a bad shock and sometimes, death. Keith Richards was knocked out by this (explains a lot) and if someone has a pacemaker, like Hubert Sumlin at Milwaukee's Pabst Theater during the Les Paul Tribute show, the go down like a sack of potatoes.

BTW- the adapter used as a "cheater plug" isn't made to have the ground lifted. If you look at it, it either has a small metal tab or a green wire with a spade terminal. The metal tab is to be secured using the screw at the center of a standard duplex receptacle (not a Decora) and the wire is supposed to be connected to the metal junction box. By design, this was never made to lift the ground- they came about when grounded plugs were new and most receptacles had two slots.

The first thing I would check is the house's wiring, using one of these:
Gardner Bender GreenD Fault Outdoor Tester GFI-3501 Electrical - Lighting - Testing Equipment - Electrical Testers Energized Circuits

If the tester shows a good circuit and the power amp is connected ONLY to the speaker wires with no other connection to the receiver, another source or preamp, your power amp may have a problem. If it's sitting directly on the receiver or preamp, it's possible that the power supply from one is affecting the audio section of the other. You can verify this by moving them apart.

 

[Rickster71]

I can't believe the original question was asked on Oct 10th.
The question was answered with simple, systematic step by step tests and instructions.
Yet were still no further than the first day.
I guess the OP didn't get the answer he wanted to hear?

 

[highfigh]

I can't believe the original question was asked on Oct 10th.
The question was answered with simple, systematic step by step tests and instructions.
Yet were still no further than the first day.
I guess the OP didn't get the answer he wanted to hear?

Everyone understands once they become the load.

 

[slipperybidness]

Yeah, hum is there with only power and speakers connected, but with 1 catch: Amp ONLY powers up when it has signal to the 12V trigger, so I MUSt have that connection to my reciever too in order to test. I suppose I could rig it up to another 12V source for testing purposes.