Please review the site Rules, Terms of Service, and Privacy Policy at your convenience. Rules, TOS, Privacy
Get familiar with the reaction system: Introducing the Reaction System

ground loop isolators ? primarily one channel buzz

I've upgraded my interconnects to double shielded, I've cleaned up and moved around the interconnects and speaker wires (from paralleling power cables). While this has helped, I still hear a bit of residual buzz (non-gain impacted), and why it is primarily just in the left speaker I'm really clueless (and 420 Colorado has come and gone...).

Since all of my audio equipment is plugged into a single Furman Power Conditioner / Sequencer it would seem I'm not having grounding issues but clearly some noise is getting into the rca unbalanced interconnects?

I'm looking at this transformer / isolator (and others), and I'm thinking about placing this right at the amp input for the mid/tw input (I actively bi-amp my speakers btwn W / Coax, and no hum is coming out of the low-passed filtered woofers).

(Last step would be to go all balanced interconnects - which would eliminate my ability to use my tube buffer/pre for the coax channels)

Any thoughts suggestions?


  • You may want to verify that it is not the amplifier itself causing the noise. To me it almost seems like a power supply issue in the amp from what you have described.

  • A single channel problem when both channels are connected to the same equipment does not sound like a ground loop problem between the equipment. Ken is right, you need to determine the source, likely the tube equipment is at fault from your description. Checking the amp is easy, just disconnect the source and short the input, does it still hum?

    I'm not deaf, I'm just not listening.
  • edited July 7

    Agreed - if it was a ground loop, you would hear it in both channels. If it were a power supply issue, you would also hear it on both channels, unless it's a dual-mono design. I'm betting a small signal tube is on it's way out.

  • Oh, and on the isolation box - they don't list all the parameters. I'm guessing it's a pair of cheap line matching transformers in there. At that price, I wouldn't expect stellar performance. It could be -10dB at 20Hz. If you end up needing one, at least the ART CleanBOX II offers useful specs on their site.

  • Yes, cheap isolators are just 1:1 transformer in a box, don't expect it to be hi-fi or hi-end despite the words on the box, though you are using a tube preamp so maybe it's good enough for you :p

    I'm not deaf, I'm just not listening.
  • I learned recently that not all RCAs are alike. I also had a noise issue with my setup in the basement. I have a bunch of ins and outs, mic, and power cables run together. Guaranteed induced noise. I took what I thought was a nice RCA cable out of the bundle and ran it absolutely by itself and still had noise. Then I started swapping every cable I had to see if any were better than the other. Much to my surprise some of what I thought were really nice pieces turned out to be noisy. Then I threw an Acoustic Research RGB cable (just using two of the feeds) in and it was silent. 😳 Huh, problem solved, but it was only 6', I needed about 10'. Hit eBay, lucked into a NOS RGB AR cable exactly like mine.

    Just throwing that out there, I'd agree with above, you have something else going on. Also, as stated the performance of the cheap transformers could be an issue.

  • Using small signal transformers as recommended above, should lead to 1:1 Jensen mu-metal transformers. They really are one of the best at this job.

  • edited July 8

    I should have mentioned I changed the tubes in the buffer/pre (no change) and then hooked up w/o this unit in the chain, same issue.

    The amp is a new Legacy powerbloc4 - (and this is a new set-up, not an amp replacement) so I need to be clear on what is ment by ‘short the input’ (not wanting to make smoke with this amp).

  • Stick a wire in the RCA hole and touch it to the outer shell. Short it. Search the interweb for "RCA shorting plug", they're a common part, were quite popular in the olden days for photo preamps with sensitive inputs. Line level signal is generally low output impedance, high input impedance, so even with the input shorted there's still 10-20kohm in there, if your amp self-destructs from this operation it was a POS to begin with ;). But first you can always just disconnect the wiring and see how much noise the amp makes with nothing connected, but often leaving the input open can result in greater noise. Another easy check if you're uncomfortable "shorting" it would be to simply switch the left and right channels at the input. If the hum stays in the left speaker then it's the amp.

    In any case, I wouldn't suspect the amp to be at fault, its a high end class-d unit with and switchmode power supply, so internally generates hum should be out of the question but you never know, maybe you got a dud. I'd hate to see you ruin the clean sound of that amp with a $20 ground isolator, or a tube for that matter.

    I'm not deaf, I'm just not listening.
  • I used a JK Audio Pureformer for years.

    Not exactly cheap but it's well made and got rid of my hum.


  • -disconnect inputs to amp, speakers quiet
    -put back inputs , swapped l and rt input, still noise in lt spkr
    -pulled tube/pre out -still noise in left speaker
    -swapped my dyi speakers - hum / buzz remained in left speaker
    - looking like issue with amp - which is a bit surprising - but why then quiet when inputs disconnected?
    - I’m contacting Legacy for next steps

    -I appreciate the input

  • Issue with speaker wire picking up AC noise?

     John H, thanks to JP I did get that email
  • John,

    Thx. I just got done looking at that as well. I went into the craw space and repositioned speaker cables where I could- no go.

    Then I took an old small speaker and connected ~directly to the amp outputs (thinking the lines to the wall that then lead to the speakers may be picking something up from house power wiring?) and yet a hum/buzz remains from connecting to amp either outputs 1&2 (left speaker), but not from amp outputs 3&4. While 3&4 are not dead silent they are very, very, quiet. 1&2 seem to be the issue. Now that doesn't eliminate AC noise getting into those channels (I didn't pull the amp out of its location) its just seems like this particular amp has a defect. The reviews on this amp have been solid, so as they used to say with Triumphs you don't want one that was built on a Tuesday...

    I just sent off a note to Legacy listing my steps to localize and resolve the issue, concluding an issue with this amp from the get-go, and looking for a replacement.

  • If you are going to remove the amp for repair/ replacement anyway it's probably good to test in a different location, preamp and speakers before sending off.

     John H, thanks to JP I did get that email
  • I agree with John. You can sometimes avoid moving the equipment by running an extension cord to a different circuit in your house. Preferably a circuit on the other leg of your panel. If you go to your breaker box you will see two columns. Choose a circuit on the opposite column.

  • edited July 9

    I'm pretty sure if the electric supply was at fault the noise wouldn't be in just one channel of the amplifier. In this case physically moving the amp to a different location will eliminate the possibility of a radiated interference inducing the hum.

  • Agreed, the extension cord method has helped me in the past with a grounding issue so I offered it. In my case the outlet was a 3 prong that did not have the ground terminated to the outlet. I should have known better when it was the only 3 prong outlet in the room.

  • I had this house built with a dedicated line from the box. But yes moving the amp to a new location (away from the other equipment) and a direct speaker connection is on the list.

    Interesting this am I received an email directly from Bill D. from Legacy saying Andy, we will get this worked out for you, and goes on with a suggestion to initially try a balanced connection.

    Impressive to see the owner getting involved, and on a Saturday… 👍

  • While going full balanced would seem to be a solution >when I connected directly from pre to amp one channel at a time- bypassing my non-balanced tube pre/buffer and the miniDSP-hd crossover, the speakers were quiet. I’d need to at a min upgrade to the miniDSP flex unit with hd and some more balanced cables.

    So before I threw in the towel (and $pend to convert to bal) I decided to pull all the cables, recheck the four wire cables to the speakers (biamped) the a/v group routed to confirm proper pairings of + and - sets (possibly the source of the problem?) and re-check each connection.

    The speakers are now finally void of any hiss/hum/buzz. Not really sure what was the cause, but going back to ground zero resolved the issue. Now time to visit the adult bev posts…

  • Glad you got it working, sucks it was such a pain.

Sign In or Register to comment.