Help with ground loop hum

greekgoddj

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Hello! :hiya:

I am having what I think is a ground loop hum between my sub (BK) and receiver (Denon) and it is driving my crazy. :( Both are pluged into the same power strip.
  1. The sub with nothing (other than power obviously) connected = no hum even when cranking up both the high-level and low-level inputs gains
  2. Connecting the sub to the receiver with the high-level cable = hum when turning up the gain for the high-level input. The gain of the low-level input making no difference (as expected)
  3. Connecting (in addition to the above set up) a low-level RCA connection between the sub and the receiver = hum eliminated from high-level, but hum appearing when turning up the low-level gain.
So the hum is sorted on the high-level input but now present in the low-level input which I still need to use. I have already tried connecting the ground cable of the high-level connection to the chasis of the receiver but that made no difference. Does anybody know what else I could try?

Thanks in advance
 
Bump.. anyone? :) I have gone through the guide linked here on sorting such ground loop, but I can't make sense of how to approach t on a setup that takes both a high and low level connection between the sub and receiver.
 
A TP-Link wifi plug near my Monolith+ was the culprit in my case. Have you anything in the vicinity that could cause interference?
 
Nope, no wireless devices nearby. I just double checked by making sure that the only two devices with power in the room were the sub and the receiver. The hum is there are long as the receiver is pluged in to the power socket (even on standby). As soon as remove all power from the receiver, the sub's hum goes away. The receiver isn't connected to any other devices either.
 
Have you tried a different socket strip for each component?

Also a different RCA to rule that out.
 
Hi, thanks. Yup, tried different RCAs, and different power sockets for the devices. Watching this, it suggest my steps are right, but it states this is if using as a stereo only system.. (by passing ground hum into 0.1 input on the sub and turning down the gain). I wish they said what to do if it isn't just a stereo setup :)
 
Just came across this page too, which suggests:

f you are connecting to a theatre system, you are already making this connection between the SUB OUT of your processor to the LFE input of the REL. In this case just leave the BLACK wire disconnected and tape off to avoid accidental shorting.

  • Solder the BLACK wire of the REL high level cable to the ring connection of an RCA plug and connect it to an unused RCA input on your system.
  • Connect the BLACK wire to the ground lug provided for phono input on integrated amp or pre-amp.
  • Connect the BLACK wire to the Earth connection for radio antenna on amplifier.

So far attaching the BK's high-level ground cable to the chasis, or an unused RCA input, or FM antenna isn't making a difference... which makes me wonder if the black strand of the high-level connection is even the ground one... o_O

Just checked BK's manual.. and yup, seems black is the ground:

To connect the high level lead you will need to connect the RED wire to the RED terminal of the RIGHT hand speakerterminalof your poweramp. Connect the WHITE wire to the Red terminal of the LEFT hand channel speaker terminal of your power amp. The BLACK wire is connected to either one of the BLACK speaker terminals of your power amplifier.
 
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My understanding is that ground loop hum doesn't alter with gain, are you sure it's a ground loop?
You could try one of these to check: Amazon product ASIN B000NVWB9O
When you say there's nothing else plugged in to the receiver, are you including HDMI cables in that statement? I'm sure you are, it's just worth checking. Cable boxes are often culprits so make sure that's off and unplugged.

How far do you have to turn the gain to hear the hum? If it's well over where you need the gain, is it really an issue? Not the best "solution", and I don't know that my OCD would let me get away with that with my subs, but something to consider.

Does the hum come through with the low level cable connected but without the high level connection?
 
Hi @Conrad. , thanks for the suggestion on that gizmo.. added to my amazon wishlist as something to try. Yup you are right, I had disconnected HDMi cables from the received too... as well as Ethernet.

The hum is already audible at my listening position with the the gain set to a level needed (about halfway) to match the rest of the setup. I am certainly not expecting to have the gain at full whack or even close to it (dangerous!) and to have no hum.

To answer the last question in your post:
  • Without either high or low level connections and both high & low gains set WAY up.. zero hum.
  • With high-level connection only, high-level gain brings in hum. Turning up the gain on low level makes no difference.
  • With low-level connection only, low-level gain brings in hum. Turning up the gain on the low-level makes no difference.
  • With both high level and low level connected, there is no hum when turning up the high level gain, but there IS hum when turning up the low level gain.
In other words... the hum IS comming from either cable (from the AVR), but the low-level connection takes the hum away from the high-level connection.

I considered if the cables were picking up noise by being near other cables etc, but have ran the cables away from any cables and the results have been the same. So I am trying to rule out noise/interferance, and hum seems to be coming via AVR.

Considering one of the AudioQuest Black Lab cables which have a separate grounding lug, but not sure if it does much different to what I have tried. There is already an oportunity for ground link to be established between the AVR and Sub... :suicide:
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Thanks again for chipping in with ideas!
 
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My guess is that there's less resistance on the low level cable than on the high level which is why the high level attracts the hum. I'm no electrician though.

You could try the greyhound cable (there was one in the classifieds recently I think) and if you get it from amazon you can return it if it doesn't work.

A cheaper, albeit less tidy version, would be to get some cable, any cable, and connect it a screw on the sub chassis to the grounding screw on the AVR. There might even be a dedicated grounding screw on the sub. I believe that that's a screw that goes through the double shielding and actually touches something inside. You could always just touch the wire at the sub end against each screw, there's no voltage between the two I don't think. Again, not an electrician.

What cables are you using at the moment? I recently replaced my cables between my pre and power amp with a much cheaper but better shielded cable and I got rid of the slight hum I was getting in my mains.

And now for the clutching at straws section!

Try connecting the sub to a different pre-out, not the sub one but either the L or R for example.You might not get much signal but it'll be interesting to see if it still hums.
 
Hi again,

The low-level cables I have used so far are a Fisual S-Flex, and a Monacor (never heard of them, came with the sub). I am primarily using the Fisual. Certainly not "fancy" cables.

So I have given your suggestion a try. I took a regular speaker wire, and screwed it down on the receiver's chasis screw, and then with the other end touched the screw on the back of the sub plate... and the hum was attenuated. Pressumably ground is finding an even easier path across the device, even if not low enough resistance to not go through the other cables. I attach to the receiver chasis by the way, because my receiver doesn't have a phono input dedicated ground connection.

My receiver doesn't have any other pre-out connections, but I also took an RCA and plugged it into an RCA input on the receiver (so no signal coming out) and with the other end of the cable I touched the sleeve/ring part of the cable to the screws at the back of the sub.. and same as above.. it attenuates the hum.

It may even attenuate it enough for it not to be audible at listening distance. Also, I think there was a difference iin attenuation when trying different screws to touch at the back of the sub.

Bizar thing is the manual for my receiver shows there should be a ground connection for AM... but my receiver doesn't have that either. I have looked only and found the same model both with and without AM/FM ground connection. I will contact Denon support and ask where the best place is to ground for my receiver.

As for a tidy solution, the AudioQuest is looking likely.

I feel like tonight I made progress, so big thanks to you @Conrad. :smashin:
 
Great news, I'm glad you were able to make some progress.

Something else to consider, we've been focussing on the sub as a culprit, but maybe the Denon isn't grounding correctly? Have you tried connecting the sleeve of the sub pre out to the Denon chassis? If the Denon plug is replaceable, have you tried a different power cord? (I'm not suggesting power cords make a difference, I'm just wondering if the cord is compromised).

Also, instead of an FM or phono ground (which are usually long screws designed to be undone by hand) see if any of the chassis screws has a ground symbol on it. My Marantz does, for example, even though that's double insulated.
 
Hi.. so i thought I had replied to this yesteday but it seems I failed to hit Post.. oopsss.

So I have been suspicious of the receiver as the culprit for some time... it doesn't have a dedicated ground connection at all.. of any type. Even though the identical model but possibly for different region, seems to have one. Still chasing Denon support on what the best place to ground it is.

Yesterday got my hands on the AudioQuest Black Lab.. used that for the low-level connection and the hum is quite lower! Low enough that is is barely perceivable at the sitting position. If I hear it, it is probably "in my head". Also this improvement is without even connecting the dedicated ground connection it has. Attaching that.. makes zero difference. This leads me to again question my receiver. (Next receivcer will have a dedicated ground connection!)

So this is all good now, but from an OCD point of view, I will still see where Denon suggest I connect the additional ground cable. For now, thanks for your help and hope the above wall of text helps others in the future.

See you!
 
Coming late to the party (thread) but for what it's worth:

I use a Marantz SR7015 with Parasound pre to an Parasound poweramp on the FL/FR, within a 5.1.2 home theatre speaker setup.

After connecting many sources (Switch, PC, BT box (Humax PVR), Bluray player etc..) ground loop galore, buzzes, hit and misses. The power source is not the cleanest yet all components are powered by the same socket. The Sub (Focal 600P) gave me a strong humm too.

I have today an 100% clean system after chasing days and nights for 6 months and what I learned was:

- The disturbances are always related in to the receiver (is it under load? properly grounded?), when taken out of the loop, the hum/buzz/frizzles stops.

- Investing in high quality RCA analogue interconnects is very important (I use Chord Clearway's atm), swapping with some el cheapo ones (£8.99) particularly at the preout of the AVR is night and day. Same goes for the sub RCA cable.

- Similar to what was linked earlier, what eliminated all other noises for me was the Palmer Line isolation box linked below - I have a single channel one in between sub and AVR, and a dual channel RCA one for my FL/FR channel coming out of the AVR PreOuts.

1 Channel: https://www.palmer-germany.com/en/products/line-isolators/5180/li-01
2 Channels: https://www.palmer-germany.com/en/products/line-isolators/5182/li-03

This is a thing of wonder, as not a single buzz can be heard no matter the source and output. I wish I knew about those boxes much earlier would have avoided endless days of frustration.

Hope this helps someone.
 

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