Ground loop?

[ratbuddy]

I've got a buzz going on when the amp is turned up past halfway. It sounds exactly like http://en.wikipedia.org/wiki/File:Mains_hum_60_Hz.ogg

It's almost never an issue because the speakers are loud enough with the amp only turned up to 1/4 for most material, but once in a while there's a bad DVD or Netflix stream with quiet audio, and I need to turn it up. That's when Mr. Hum shows his face.

I've heard ground loop isolators will change the sound, and I don't want to do that. I just want to get rid of the AC noise. Any way to do that?

The amp is a 2 channel integrated, no grounding pin on the plug, connected via RCA to a sound card, the cable box, and a switch box that handles all the consoles. The only thing using a grounded plug is the HTPC, and there is no grounding post on the amp. There is no buzz on the cable or console inputs, just the HTPC.

Thanks :beer:

[MadMan007]

What's the model of the amp?

Ground loops can be a PITA to troubleshoot because it can loop with anything on the same circuitbreaker or even sometimes in the house as a whole. For troubleshooting steps you might want to start by making the system as simple as possible. Take everything out but the PC and the amp, even though you say the other parts don't have the hum that could be because they are the source of the ground loop.

Do you hear the hum with other sources selected but not playing when you turn the amp up as loud? It's possible the amp itself has a bit of hum, if you know where the transformer is in the amp turn on just the amp and see if you hear any buzzing. Transformer buzz is different from ground loop hum but can sound similar.

[ratbuddy]

What's the model of the amp?

Ground loops can be a PITA to troubleshoot because it can loop with anything on the same circuitbreaker or even sometimes in the house as a whole. For troubleshooting steps you might want to start by making the system as simple as possible. Take everything out but the PC and the amp, even though you say the other parts don't have the hum that could be because they are the source of the ground loop.

Do you hear the hum with other sources selected but not playing when you turn the amp up as loud? It's possible the amp itself has a bit of hum, if you know where the transformer is in the amp turn on just the amp and see if you hear any buzzing. Transformer buzz is different from ground loop hum but can sound similar.

The amp is an NAD C320BEE, and I'm going to try all that stuff now, will post back with results.

edit: Well, I turned the volume up and switched between the inputs with no sources active. The cable box is nearly dead silent, unless the volume is at 75% or so which never ever happens. Once the knob goes that high, it gets a slight buzz at the same general frequency. The console switchbox (Wii selected but not on) gave a little more noise overall, but much higher in frequency. A bit like white noise, even. Also not until very high volume.

Mr. HTPC is the naughty one, the buzz at half volume is very noticable. I guess the next step is to move the HTPC to another input on the amp to rule that out as the cause, then go from there?

[dudleycpa]

Can you check to see that the ground (at the outlet) is actually ground? IIRC it is not uncommon for them to be "ungrounded". I know this is a major pain in the buttock but you could try to do this by moving the HTPC to a different circuit (i.e. different circuit breaker).

I sure you have thought of doing this but it never hurts.

Madman007 is right - trying to figure out something like this is a PITA.

[TTP]

did you try taking the power off the outlet and putting in a UPS with line conditioner or an active UPS that allows the device to pull power from the battery source instead of the outlet pass-through?

[ratbuddy]

The nearest outlet is about 20 feet away so that's out, and I don't own any type of UPS.

I did check the outlet with one of those little plug in testers, and it seemed fine.

Not sure if this matters, but I'm using a rather long cable to connect the sound card to the amp. I think it's 20 feet, maybe 25, with a stereo plug on one side and RCAs on the other. Maybe I'll grab a shorter one anyway, the cables are a mess back there.

[Sir Barton]

Sounds to me that you need an isolator for your cable line. Cable wires are a large contributor to the hum, and can be fixed with an isolation transformer. It may not be introducing noise with only the cable box plugged in, but once you fill up more inputs youre adding more potential spots to complete the loop. Parts Express sells the transformers for ~$10.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=180-075

[ratbuddy]

Sounds to me that you need an isolator for your cable line. Cable wires are a large contributor to the hum, and can be fixed with an isolation transformer. It may not be introducing noise with only the cable box plugged in, but once you fill up more inputs youre adding more potential spots to complete the loop. Parts Express sells the transformers for ~$10.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=180-075

Hmm, it says "A passive design does not affect your analog cable tv signal strength (not recommended for use ondigital cable or cable modem installations)."

I've got a digital box though :-/

[TTP]

I would still suggest you put a UPS with a line conditioner between the amp and the outlet to at least address any line noise from the outlet.

[Joeteck]

Some amps have a grounding screw, that you can connect a wire to it, and then ground it at the outlets screw that holds the face plate on.

http://www.microsoft.com/windows/windowsmedia/images/howto/HTurntableReceiverGround.jpg

[Sir Barton]

Some amps have a grounding screw, that you can connect a wire to it, and then ground it at the outlets screw that holds the face plate on.

http://www.microsoft.com/windows/windowsmedia/images/howto/HTurntableReceiverGround.jpg

That screw is for a phono preamp ;).

I would still suggest you put a UPS with a line conditioner between the amp and the outlet to at least address any line noise from the outlet.

A UPS isnt a good solution for ground loop issues. A ground loop is what you get when multiple circuits share the same ground. If youre running an 8 outlet UPS, all 8 of those outlets will be plugged into the same ground at the receptacle.

Hey ratbuddy....have you tried plugging your components into separate wall sockets? Is the splitter coming off of the main cable line grounded?

[nd4spdbh2]

I would suggest running a small say 18 awg wire between one thing at a time. I know i had a PITA ground loop even with running grounds to each component via their power plugs. Putting a wire between the amps case and the backplate of the sub's amp completely got rid of the problem. Just take a screw out of the metal case housing of the components sand the area down to get bare metal and use a wire connector and connect the wire between both components.

[CompuTamer]

The amp is an NAD C320BEE, and I'm going to try all that stuff now, will post back with results.

edit: Well, I turned the volume up and switched between the inputs with no sources active. The cable box is nearly dead silent, unless the volume is at 75% or so which never ever happens. Once the knob goes that high, it gets a slight buzz at the same general frequency. The console switchbox (Wii selected but not on) gave a little more noise overall, but much higher in frequency. A bit like white noise, even. Also not until very high volume.

Mr. HTPC is the naughty one, the buzz at half volume is very noticable. I guess the next step is to move the HTPC to another input on the amp to rule that out as the cause, then go from there?

My computer also causes a slight hum through the speakers... it might be the soundcard isn't grounded properly... are you using the on board, or an add on card?

[ratbuddy]

My computer also causes a slight hum through the speakers... it might be the soundcard isn't grounded properly... are you using the on board, or an add on card?

Auzentech X-Raider with OPA627 opamps. It was making the buzz with onboard sound too.

[nd4spdbh2]

Auzentech X-Raider with OPA627 opamps. It was making the buzz with onboard sound too.

like i said make a connection between the computer case and amp case with a wire... id be willing to bet the humming goes away.

[Aynjell]

like i said make a connection between the computer case and amp case with a wire... id be willing to bet the humming goes away.

I'd be almost willing to try this myself, if it resolved it, I'd find a nice way to set something up like this with some sort of quick disconnect. Interesting this would happen though. I bet you could setup some kind of clamp that grounds to the screw.

Supposedly though, even network cables can extend your ground loop elsewhere. It can be something in your living room that's causing it, for example. Something I'll try very soon though.

[Joeteck]

That screw is for a phono preamp ;).



None-the-less, a grounding location.