Hum (Ground Loop?) at Speakers
scubalab
Posts: 3,101
I recently swapped equipment (speakers, amp, pre-amp, and turntable) in my 2 channel rig. I’ve noticed a very loud, annoying buzzing coming from both speakers. It is indicative of a ground loop hum (120 Hz, no change when moving the volume knob, and goes away when I disconnect the pre-amp from the amp). However, I tried a cheater plug on the amp and it did NOT resolve it. The pre and the TT do not have grounded plugs. Disconnecting all of the inputs also does not eliminate the problem. I tried two different receivers as the pre amp and both do it. I also tried different interconnect cables and that didn’t work either. I’m at a loss.
I don’t recall the buzz when I had the Acurus amp, but with the B&K, it’s there. Here’s my setup:
Carver Hr-742 receiver (pre-amp)
Rega RP-1 TT
B&K ST125.2 amp
Polk LSi9 or Polk Monitor 5JR+ speakers
Any help is appreciated.
I don’t recall the buzz when I had the Acurus amp, but with the B&K, it’s there. Here’s my setup:
Carver Hr-742 receiver (pre-amp)
Rega RP-1 TT
B&K ST125.2 amp
Polk LSi9 or Polk Monitor 5JR+ speakers
Any help is appreciated.
Comments
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Is the amp new (to you), Al?
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I would check the plug wiring, and make sure connections are tight. They will loosen over time
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WARNING: I am a Neanderthal at best when it comes to the fine art of grounding! That said, I've done my time fiddling with hum, induced and otherwise, so I will (still) offer some suggestions ("as-is" and FWIW):
Wouldn't a ground loop be 60 Hz? 120 Hz is full-wave rectified, unfiltered DC.
That said, some ideas/thoughts.
If you have any nonpolarized plugs, try flipping any one of them in the AC mains outlet.
Another simple but vexing problem could be induced hum -- e.g., a power transformer in one component is closer to another component than it was, and is now able to induce a signal into the second component. This can be a common problem with, e.g., a turntable and an amplifier, or a power amp and preamp. Move one component with respect to the other and see if the hum gets louder or softer. Turning one component at right angles may alter the amplitude of induced hum, too.
In terms of troubleshooting, I like clipleads.
Y'all knew that already.
First and most straightforward, of course, is the reductionist approach. Take as much out of the system as you can. If there's no hum, start adding back components until there is.
Remember that things like cable TV/internet inputs can be sources of hum.
Another approach, using the aforementioned clipleads: Take a cliplead (or a piece of wire of sufficient length, with clipleads attached to either end, if need be), and connect a grounded point on one component to another. You may be able to "shortcircuit" a ground loop and knock back the hum by trial and success*.
There are also isolators for ground loop elimination. They're standard toolbox equipment in the pro audio/portable (PA) audio game, but they can be used in the home, too. I think they use 1:1 transformers for isolation.
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* Which is a lot like trial and error, but with a better attitude
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Oh
I just re-read the OP. "Very loud" sounds like a cable issue (broken wire in the ground or return, or just poor connection).
Then again, if the naked amplifier (i.e., just the amp, with NOTHING connected to its inputs, just connected to loudspeakers) is doing it -- it's a problem with the amp.
I am also assuming nothing else is plugged in/turned on near it... ideally, nothing at all else on the same circuit. If it's possible to short the inputs for troubleshooting, that's the best case.
If it is 120 Hz hum, from the amp alone, it sounds like to me (the ol' tube guy) like power supply (i.e., bad filter capacitors)... I assume it has a linear power supply
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OK, so a little more info...
Mike - yes, the amp is new to me. Bought from a trusted forum member a couple weeks ago.
rpf65 - I will have to check the wiring connections inside the amp. The power cable is securely seated in the socket outside.
Mark - I was going off info on PS Audio’s site about amplifier hum here:
https://www.psaudio.com/ps_how/how-to-find-and-fix-hum/
Mine is more of a buzzing coming from the speakers and sounds just like the 120 Hz sample. Which they say is ground loop.
I only have the amp, pre (receiver), and turntable in the system. When it’s JUST the amp connected to the speakers - NO BUZZ/HUM!
When I connect the receiver - BUZZ/HUM.
When I connect the turntable - BUZZ/HUM STILL THERE.
When I use the cheater plug (eliminating the ground lug in the amp PC, BUZZ STILL THERE.
I’ve tried two different receivers as pre-amps and both do the same thing. I’m convinced it’s the amp, but can’t figure out why eliminating the growing on the amp doesn’t resolve the problem... And I can’t figure out why the buzz goes away when I disconnect the pre-amp?
I’ve tried plugging the amp & receiver in the same receptacle and separate ones - no change. I’m confused. -
If your amp doesn't produce the buzz, it isn't the amp.
If you connect your AVR and it buzzes, it's the AVR.
Same with the turntable.
No buzz, no equipment issue, at least for ground loop. Buzz, equals issue.
Try the speakers wired straight to speaker terminals of the reciever. -
Hooked the speakers directly to the receiver - NO BUZZ.
Connected my phone to the amp (via 1/8” headphone plug to RCA) - NO BUZZ.
It’s only when the amp and receiver (pre) are on together that there is the buzz (grounded or ungrounded).
I also noticed that although the buzz does not change with volume changes on the pre, a secondary hum becomes apparent (deeper frequency) when the volume knob is turned towards max.
The turntable connected or disconnected has no affect on the buzz. -
OK, so a little more info...
Mike - yes, the amp is new to me. Bought from a trusted forum member a couple weeks ago.
rpf65 - I will have to check the wiring connections inside the amp. The power cable is securely seated in the socket outside.
Mark - I was going off info on PS Audio’s site about amplifier hum here:
https://www.psaudio.com/ps_how/how-to-find-and-fix-hum/
Mine is more of a buzzing coming from the speakers and sounds just like the 120 Hz sample. Which they say is ground loop.
I only have the amp, pre (receiver), and turntable in the system. When it’s JUST the amp connected to the speakers - NO BUZZ/HUM!
When I connect the receiver - BUZZ/HUM.
When I connect the turntable - BUZZ/HUM STILL THERE.
When I use the cheater plug (eliminating the ground lug in the amp PC, BUZZ STILL THERE.
I’ve tried two different receivers as pre-amps and both do the same thing. I’m convinced it’s the amp, but can’t figure out why eliminating the growing on the amp doesn’t resolve the problem... And I can’t figure out why the buzz goes away when I disconnect the pre-amp?
I’ve tried plugging the amp & receiver in the same receptacle and separate ones - no change. I’m confused.
Occam's Razor would lead me inexorably to: Ground loop between Rx and amplifier -- or something else going on.
Keep it simple for troubleshooting -- if just the preamp does it with the power amp, that's the system you should use to troubleshoot.
Balanced or unbalanced interconnects?
Try a clip lead between some ground point on the preamp and a ground point on the power amp. back a screw part way out if need be to find a ground (e.g., on the power amp) -- I assume there's a ground lug on the preamp(?).
Here's another thought. If you're using unbalanced cables -- and keep the volume
very low if you try this!! -- pull one interconnect from the preamp into the power amp half-way out of the input jack on the power amp. If the ground is common between the two channels on the input jack panel, there may still be signal passed by both channels but one ground is lifted. The buzz might get (EDIT) quieter or (of course) you might get a loud buzz.
Have you ever read Rane's tech note on grounding and system interconnection?
If not, I recommend it:
http://www.rane.com/note110.html
This one's worthwhile, too:
http://www.rane.com/note151.html
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Hmm this seems to be an interesting situation, I can say definitively that the amp did not exhibit this issue in my setup. It is strange to hear that the amp doesn’t to it with anything connected to it but does when something is hooked to it. Have you verified the switches on the back are set to the right position still (balanced vs unbalanced)?2 Channel in my home attic/bar/man cave
2 Channel Focal Kanta 3 I Modwright SWL9.0 Anniversary Pre I Modwright PH9.0X I Modwright KWA-150SE I VPI Prime Signature w/ Soundsmith Zephyr MIMC I Lumin U2 Mini I North Star Designs Intenso DAC I Audience OHNO ICs/Audience Furutech FP-S55N and FP-S032N Power Cables/Acoustic Zen Satori I Isotek Sirius -
Called and we did some testing.... its not the circuit, its not the RCA's, its the pre-amp/amp combo.
We even ran a extension cord from his dedicated outlet and still got hum with the pre-amp and amp in the mix...."....not everything that can be counted counts, and not everything that counts can be counted." William Bruce Cameron, Informal Sociology: A Casual Introduction to Sociological Thinking (1963) -
Do you have any inputs connected at the preamp when it buzzes, or just the output to the amp? If so, can you try another output? You could also wiggle the RCA cables on the preamp and see if maybe you have a broken connection with the outer shield.
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Dan and I did a lot of troubleshooting (below) and unfortunately nothing eliminated the buzzing. All was done with NO input sources connected to the pre.
Ran extension from dedicated outlet in the HT. No luck.
Grounded the receiver to the amp. No luck.
Connected pre-amp to amp using headphone out on the receiver to the amp. No luck.
Zach - I did double check the balanced switches and they are correctly set to ‘unbalanced’. Obviously, when I switch to ‘balanced’ the buzz (and any sound for that matter) goes away.
I will try a different source tomorrow. I have an Oppo I can connect. It has a grounded PC. I can also try moving the amp to the HT and connect it to my Marantz via balanced ICs and see if balanced eliminates the buzz.
Doc - I’ll have to try the common ground test (pulling one RCA channel slightly from the amp) later. I’ll also be getting my read on with your references links.
I honestly thought switching the receiver would fix the issue earlier today. When that didn’t work, I would have bet a lot that the cheater plug would have worked.
Open to any other ideas! -
More random thoughts (brain droppings, as George Carlin might've put it):
1) Does the preamp/power amp combination buzz if the preamp is off?
2) You said you used a cheater, but if you said on which component you used it -- I missed it! Did you try lifting the AC mains ground on just the preamp, just the power amp, or both?
3) I presume you don't have the preamp plugged into an accessory socket on the power amp, do you?
4) Do you have any of the components plugged into any sort of power conditioning? If so, you might want to try one or both just plugged into the wall.
5) Perhaps, just for grins ("for shoots and Googles" as I like to say), you might want to try plugging one of the two components (e.g., the power amp) into a different AC circuit than the other one. E.g., get a big ol' extension cord and run it to another room (or at least an outlet on another breaker).
5a) What, if anything, else is on the same AC circuit as the amp and preamp?
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mhardy6647 wrote: »More random thoughts (brain droppings, as George Carlin might've put it):
1) Does the preamp/power amp combination buzz if the preamp is off?
No. When I turn the preamp off, buzz stops.mhardy6647 wrote: »2) You said you used a cheater, but if you said on which component you used it -- I missed it! Did you try lifting the AC mains ground on just the preamp, just the power amp, or both?
Just the amp. The pre-amp (receiver) just has a two-prong plug.mhardy6647 wrote: »3) I presume you don't have the preamp plugged into an accessory socket on the power amp, do you?
No.mhardy6647 wrote: »4) Do you have any of the components plugged into any sort of power conditioning? If so, you might want to try one or both just plugged into the wall.?
No. Tried multiple outlets, no power strip or power conditioner. One outlet does have a splitter (with USB plugs) on it.mhardy6647 wrote: »5) Perhaps, just for grins ("for shoots and Googles" as I like to say), you might want to try plugging one of the two components (e.g., the power amp) into a different AC circuit than the other one. E.g., get a big ol' extension cord and run it to another room (or at least an outlet on another breaker).
Tried this. Didn’t work...
Tried two separate circuits and even tried both on the dedicated circuit to the HT.mhardy6647 wrote: »5a) What, if anything, else is on the same AC circuit as the amp and preamp?
A couple receptacles, a light & ceililing fan, and an electric piano. I wondered about this, but the buzzing still exists when plugged into different circuits.
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mmmmm... interesting.
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mhardy6647 wrote: »mmmmm... interesting.
Yeah... I’m at a loss!
Wondering if balanced ICs will fix it. Will try that later this week. -
I'll tell you exactly how I had it setup just for information sake.
Used unbalanced interconnects, all components on the same circuit via Belkin power conditioner. The amp was on the same circuit but plugged in directly to the wall vice the conditioner. If you were closer, I'd come grab it and throw it back in my system for testing sake to see if something has changed with the amp. Did the amp exhibit this from the start or did it just develop?2 Channel in my home attic/bar/man cave
2 Channel Focal Kanta 3 I Modwright SWL9.0 Anniversary Pre I Modwright PH9.0X I Modwright KWA-150SE I VPI Prime Signature w/ Soundsmith Zephyr MIMC I Lumin U2 Mini I North Star Designs Intenso DAC I Audience OHNO ICs/Audience Furutech FP-S55N and FP-S032N Power Cables/Acoustic Zen Satori I Isotek Sirius -
Hey Zach,
I appreciate the help here. Yeah, the setup did this right from the start. I was wondering if you had it set up with balanced or unbalanced ICs. I know my pre is not the best (I was using an old 5 channel Denon AVR initially and in trying to troubleshoot), so the first thing I did was swap in the Carver receiver. Unfortunately both exhibit the same issue with the amp. I also know my interconnect cables are not the greatest (first I tried Monster (I think) and then generic). Neither of these cables had any issues with the prior setup and amp (Acurus A80). There are a couple other things I want to try. I'd like to try balanced interconnections. Then, I have another B&K amp (AV5000) I can try to see if that one causes the buzzing at the speakers. I may try moving the amp and running with different sources.
By the sounds of it, I thought this would be a quick/easy fix with a cheater plug...
I don't know if this makes a difference, but the buzzing does NOT go away when music is playing. However, since it does not change with volume, it's usually 'washed out' by the music. But, at lower volumes, it becomes apparent. -
sounds like different ground potentials somewhere.
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sounds like different ground potentials somewhere.
clipleads, man -- clipleads.
The great equalizer.
FWIW, I am pullin' for the balanced connection option to obviate the issue, but that's not even a really a SWAG.
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These problems you are having are the exact same issues I am currently experiencing in my home theater.
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Conradicles wrote: »These problems you are having are the exact same issues I am currently experiencing in my home theater.
look at the cable line if you have one hooked up in there somewhere -
Just a thought here as I'm following this thread, but, does the input impedance on the amp come close to the output impedance/level on the receivers you are trying to use? Granted, it shouldn't make that much of a difference between components but you never know. I used to have a 125.2 but with a PT3 Series II preamp and never had an issue. However, I've never tried to use a receiver as a pre either.
Talking about things I know little about obviously (as I'm sure someone on here will have more authority to say on the subject) but might be worth looking into...Remember, when you're running from something, you're running to something...-me -
Do you have continuity from the center ground IEC pin to any of the outer shields of the RCA terminals?
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I believe the problem is related to the preamp output on the receiver. As a test run a connection between the "tape out" of the receiver and the amp. However, first reconnect both the right and left preamp/amp connections on the receiver. If there's no humming be careful in testing since the "tape out" is before the volume control.
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Do you have continuity from the center ground IEC pin to any of the outer shields of the RCA terminals?
I'll have to check tonight.
As another update, I tried another B&K amp that I have (AV5000) and get the same exact buzzing. So, I don't think it's the amp. I plan to try with other pre-amp sources tonight (both sources I have tried so far are not grounded - just have two-prong plug). I can try using my Oppo with RCA connections, as well as my Marantz with XLR.
I plan to move things around too. I doubt this has anything to do with it, but I'm using a new rack as well. I changed everything (except the pre-amp and speakers) recently - amp, turntable, rack - and that's when I noticed the hum. -
KennethSwauger wrote: »I believe the problem is related to the preamp output on the receiver. As a test run a connection between the "tape out" of the receiver and the amp. However, first reconnect both the right and left preamp/amp connections on the receiver. If there's no humming be careful in testing since the "tape out" is before the volume control.
I'll give this a try Ken. I'm wondering if by sheer coincidence I had TWO pre-amps (the Denon AVR and the Carver) with bad preamp outputs since both cause the hum. I'm thinking it HAS to be the pre since two different amps exhibit the same hum.
I can try this using my phone as a source (since I can control the volume at the phone). -
As I stated in someone else's thread, I had a tight-gripping rca cable once that pulled the outer shield from an older AVR.
Does it buzz on all input selections, not the actual inputs themselves? What happens when you select another input? Does it have a tape monitor function, is that selected? Are the speaker levels in the setup menu turned all the way up? -
As I stated in someone else's thread, I had a tight-gripping rca cable once that pulled the outer shield from an older AVR.
Does it buzz on all input selections, not the actual inputs themselves? What happens when you select another input? Does it have a tape monitor function, is that selected? Are the speaker levels in the setup menu turned all the way up?
It buzzes on all input selections except the tuner. I did check that last night. I'll have to check the tape monitor function tonight. Since I'm using an older Carver receiver (not the AVR), I'm not sure how to check the speaker levels... -
I don't think the problem is with the preamps being bad, I believe it is more to do with how the grounding works when removing the grounding connections on the receivers. There is circuit ground and chassis ground and most designers connect the two only at one point. This is why I suggested to reestablish the preamp/power amp connections before trying the "tape out".
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