Ground loop with P15?

I’m stuck. I have a P15 power plant out of which everything in the system is plugged and am still running into hum issues. I started the day with three hum issues, one 120 Hz and two degrees of very recent 60 Hz (bass), and thankfully solved the louder one of the latter (additive effect?). A power cord had partly come out of the cable TV box adapter.

The two:

  • 120 Hz lightly audible from several feet away
  • Bass hum (60 Hz), forcing me to turn down my dac’s volume control from full to -11 dB to minimize hearing it.
  1. There is a light 120 Hz hum that starts when I turn on my Lampi Golden Gate dac and insert the rectifier (Sophia 274B), whether with 300B or 45 Mesh tubes (tube setting adjusted on back panel). It doesn’t change with the volume. To test, I shut down and unplugged the P15, unplugged all the power cords in it and then plugged the dac directly into the wall outlet the P15 normally uses. Hum was still there but a bit softer (no bass hum). I also swapped in a Modi 3E dac (solid state), which eliminated the hum, but Lampi said that’s irrelevant.

  2. Bass hum (60 Hz). If there’s another AC connector not fully plugged in, I can’t find it. Disconnecting other ICs had no effect. The only changes to the system made recently were swapping fuses and using the second version of High Fidelity’s contact enhancer on all fuses, tube pins and connectors that didn’t already have it. When I moved the dac and preamp to the wall outlet, there was no bass hum (active speakers still on). That’s all I know. Any ideas? (The cheater plugs I have don’t take Furutech size connector prongs, so I couldn’t pursue that approach today).


  • P15 (from Furutech GTX-D outlet)
  • modified Oppo 203, digital only (coax to dac)
  • Lampi Golden Gate 3 dac w/ EML 45 Mesh tubes
  • VAC Master preamp (RCA from dac)
  • ATC 50 floorstanders (active, XLR from preamp)
  • JL Audio e-110 subs (XLR to RCA, Cardas adapters with pin 1 floated)
  • cable TV box w/ isolator inline
  • SSD to Oppo via USB
  • all cables/cords are WyWires Diamonds, except one PAD Neptune coax, a PAD HDMI from the cable box to Oppo, and a AQ Vodka HDMI to the TV

If you disconnect the cable to the cable box does the hum go away? Also do you actually have any fully balanced gear in that lineup that require balanced IC’s or adaptors? Your VAC preamp has two sets of SE outputs so don’t know why you are using adaptors to the SE inputs of the subs.

Subs are RCA, which is why the adapters at the their end, with pin 1 disconnected. If you mean power to cable box, hum continues after I shoved the WyWires connector all the way in the box’s adapter. Moving that PC to a wall outlet didn’t change anything, although that outlet is on the same circuit as the P15. I didn’t disconnect the cable box coax though, but it does have an inline isolator on it. I’ll have to check that. Checking that addresses the 120 Hz hum, not the 60 Hz one, which is most annoying and recent.

Hi @highstream

You haven’t mentioned what you have done so far to troubleshoot the issue, so I will start with the basics. Disconnect devices one by one. As the noise goes away, the disconnected wire is the cause of the hum. From there, you can inspect/analyze matters further.

Good luck!

Actually, I disconnected both power and ICs one by one and got nothing, with the limit that with active speakers there needs to be at least one going (after trying the subs, I left them disconnected). That’s also why I tried isolating the dac and then both dac and pre via the wall outlet, which did largely kill the hum, leaving a light one from the dac. All that’s left is trying cheater plugs, although I would think at this point they would be more likely to find the 60 Hz one via a better connection. Reading Paul’s comments about ground loops, I got the impression the P15 would prevent that. I also have the impression that Mesh tubes are more electrically demanding, perhaps on capacitors.

When the active speakers are disconnected from everything except power and they are turned on, do you get a hum?

With other things on or off?

  • Right now, with only the P15, dac, lps and both sets of speakers on and fully connected, there is only a barely audible ear-to-speaker hash.
  • Turning on the preamp adds a light hum that moves with the VC.
  • Disconnecting the ATC’s ICs (but not the subs’) kills it, leaving only the light higher constant buzz from the GG’s innards lightly audible from 8’ away. The Oppo, TV and cable box were off.
  • With everything turned on and the dac’s VC setting at -12dB, hum can be heard from the listening position (7.5’) with nothing playing.

The best way to investigate this is very, very, methodically.

Start with everything disconnected from everything else and everything turned off, even disconnect the P12 from the wall. Plug speakers into the wall. If there is a hum, call the speaker manufacturer. If there is no hum, connect the speakers to P12 with nothing else connected to the speakers or the P12, turn on the P12 and the speakers is there a hum? If so, discuss the matter with PSAudio. if not, power on the next device that connects to the speaker without connecting the speakers and turn it on. Is there a hum? If yes, the power supply of that device causes a hum, contact the manufacturer of that device. If no, Connect the device to the speakers, if hum there is some kind of AC discrepancy flowing between audio wires and speaker caused by that device being connected, contact the manufacturer of that device. Repeat that process until you figure out which device(s) are causing what hum.

I think you get where I am going. It is tedious and time-consuming, but this is the best way that I know how to figure out what is causing the problem.

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I have done much of it already, but will go back.

One test I did today was with the GG dac: unplugged the ICs and ran an extension power cord to a different electrical circuit’s outlet. Got the same the higher pitched hum from its innards, which starts when the rectifier tube is inserted. That suggests to me either the condo has a ground loop or the dac is producing the noise on its own.

Does the (P15) regenerator block low-level DC voltage on the AC power line that can cause a component’s power transformer to hum? Someone on another forum suggested that might be the case for the 120 Hz hum seemingly coming from the Golden Gate dac’s chassis. He suggested the Humdinger — HumDinger DC Line Blocker – Audio by Van Alstine

I had a similar thing going on with my P10 for my HT rack. epson projector, 2 multi ch amps, 1 processor,1 Oppo, my network gear, Roon CORE, and NAS both with LPS.

All units except Projector and Oppo were 2 prong. When I swapped out anthem for marantz, hum. When I took out the HDMI from both oppo and projector, hum gone. I put on the 3->2 adaptor at end of power cable for those 2, hum gone. I ended up giving back the 7706 and got the AVM70 (coming from avm60). No hum with Anthem any why hooked up. No cable, no nothing in the system. All self contained. no idea why the loop happend. No idea why the anthem did not expose the hum.

All my connections are 3 pronged, and the XLR-RCA adapters for the subs have pin 1 floated.

I finally got the dac over to a local A-V shop and had it up on the test bench. At first, when I turned it on with the EML 45 mesh tubes, only the rectifier turned on, while the 45’s remained room temp. Weird. Then I tried the WE 300B’s and they seemed to light up, although the tubes again didn’t warm up to the touch. Then I went back to the 45’s and this time the mesh lighted up. At that point, ear to the unit it was dead quiet. What can I say? That suggests I’ve got a problem in my electrical system, perhaps even in the breaker box. Next step is taking a look at it and maybe a Hum-X or maybe one of Van Alstine’s boxes that blocks stray DC. However, my place is apart right now due to water damage and further testing will have to wait until new flooring is in and the living room returned to listening capability.

Why would a 120 Hz hum occur with a tube dac but not a solid state one?

Hum is experiences two basic ways;
-) ground loop.
-) inductive coupling magnetic fields (120 Hz suggest a power supply issue as line level is 60 Hz by default).

Take the P15’s power cord and look at the AWG. Take a TEMPORARY smaller AWG power cord and use that. The higher DCR should make the hum go up with the smaller AWG power cord. Did it impact the hum? Likewise a larger AWG will decrease the ground loop potential voltage and decrease the hum.

If this seems to be unnotable, the hum seems to be induced through a power supply. Isolate the device that causes the hum.

Do Not use cheater plugs on three prong equipment that isn’t double insulated! There is no protection from chassis faults and if you touch the chassis, you are the return. Ouch. OK for testing but not to be left ungrounded.

Don’t float the shield Pin 1. A shield is an attenuator, not an antenna. With Pin 1 open, it is a resonant antenna. A shield attenuates ingress / egress based on frequency as it moves through the shield. Both ends have to be grounded for a shield to work as a shield. RF will resonant on an ungrounded shield and inductively couple as an absorbing clamp test will show.

The solution is to fix the inductive coupling and/or the ground potential difference that causes the ground loop. Opening Pin 1 doesn’t fix the ground problem, it masks the ground differential and creates another RF inductive resonant problem.

SPG, single point ground, cable shields aren’t shields.


Very important to separate hum coming directly from a component and hum heard through your speakers. If your DAC (or any other component) produces hum all by itself plugged in but not connected to other components or speakers then DC on the AC line is very likely the cause. The DC blocker products should resolve this.

My earlier version of amplifier from Innersound had toroid transformers that were not potted (epoxy encapsulated) and produced a relatively low level of hum (could be 120Hz because the output windings have full-rectifiers). Homemade DC blockers solved this issue.

After upgrading to Sanders Sound Systems Magtech amps (with potted toroid transformers) that hum is gone.

A Wyred power conditioner with a DC snubber arrived today. Placed between wall and P15 and using an OEM power cord, it eliminated the audible hum from the speakers at the listening position (9’). I have to jack up the preamp’s volume knob to hear anything, which is light hash with a deep bass tone. Not sure where to look for that. In any case, I have only a few recordings that need that much gain.

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