Diagnosed and solved my ground loop issue, but looking for a safe solution

[xevman]

So to break it down I have a very annoying ground loop buzz after adding an additional amplifier to my chain of devices. The problem was with one of the amps, buzz came through the my Woo Audio WA6-SE and was very loud at all volumes. I removed everything including my PC so it was just the 2 amps and 1 dac so my setup looked like this.

D90 DAC -> A90 AMP (balanced xlr)
D90 DAC -> WOO WA6SE (unbalanced rca)
Connected simultaneously and PC was also disconnected from this chain so the issue is between the dac and amps


I decided in order to diagnose this I had to lift the ground on both the D90 and A90 so I went and did so by insulating the ground pin on both wall plugs. Now before you call me an idiot I didnt just blindly do this. I got my multimeter out set it to volts ac and checked to see if the chassis on both the A90 and D90 were live but the multimeter read 0 volts to ensure it was safe to proceed. Not to my surprise it removed the ground loop and the Woo Amp became silent.

Now I did a continuity test between each of the devices with my multimeter and all the devices beeped when I tested them for continuity between each other does this mean now they effectively are grounding using the WA6-SE mains ground instead of their own mains ground?

Secondly is there a safe long term solution I can possibly try rather than doing this cheat method and lifting the ground? I'm going to pack up and disconnect the amp until I know that there is a long term safe fix for this issue which I can try.

Any help advice or insight would be greatly appreciated...

 

[Oklei]

The reason for the ground loop "sound" is most likely current over the rca cable shield. You could use an audio isolation transformer like this one in the rca connection between d90 and woo wa6se: https://www.audiophonics.fr/en/audi...tion-transformer-ground-loop-rca-p-13755.html

 

[xevman]

The reason for the ground loop is most likely current over the rca cable shield. You could use an audio isolation transformer like this one in the rca connection between d90 and woo wa6se: https://www.audiophonics.fr/en/audi...tion-transformer-ground-loop-rca-p-13755.html

Thank you for the suggestion I'll give this a try.

 

[xevman]

https://www.selby.com.au/unbalanced...taWU8ijGsiDNsY2tfK0Tzd8q5VhQAKnQaArLFEALw_wcB

Just to clarify this is the same thing right?

 

[Oklei]

essentially yes. this one has no specs for thd and snr. the specs only say it will distort with voltages greater 1.78V rms. whatever that means. you could get some audible sound changes with this one but not for sure ofc.

 

[Pluto]

is there a safe long term solution I can possibly try

See what you can achieve with interconnects with the screen connected at one end only.

 

[AnalogSteph]

That's what happens when you buy a $1299 tube headphone amplifier that's an IEC Class I device (maybe not such a bad idea in gear involving vacuum bulbs) but clearly is not using any input transformers for galvanic isolation. Wouldn't have happened with a $99 JDS Labs Atom.

Unbalanced connections between two Class I devices are just fundamentally broken when neither uses galvanic isolation. Folks designing boutique tube audio gear aren't necessarily aware of that, and may be expecting you to be using a classic hi-fi CD player or DAP or something (Class II / floating).

You need a line-level isolator between the D90 and WA6SE. I would suggest a Behringer HD400 at the very least (plus cabling), though you can get others with fancier transformers for more money as well. (You can spend as much as for the whole HD400 on a Hammond or Lundahl transformer at a parts distributor. Those are up to a higher standard then, of course, but at consumer line level the little Behringer generally gets things done.)

The part that I'm wondering about now - this should only have affected the WA6SE. There wasn't anything audible on the A90, right?

 

[xevman]

That's what happens when you buy a $1299 tube headphone amplifier that's an IEC Class I device (maybe not such a bad idea in gear involving vacuum bulbs) but clearly is not using any input transformers for galvanic isolation. Wouldn't have happened with a $99 JDS Labs Atom.

Unbalanced connections between two Class I devices are just fundamentally broken when neither uses galvanic isolation. Folks designing boutique tube audio gear aren't necessarily aware of that, and may be expecting you to be using a classic hi-fi CD player or DAP or something (Class II / floating).

You need a line-level isolator between the D90 and WA6SE. I would suggest a Behringer HD400 at the very least (plus cabling), though you can get others with fancier transformers for more money as well. (You can spend as much as for the whole HD400 on a Hammond or Lundahl transformer at a parts distributor. Those are up to a higher standard then, of course, but at consumer line level the little Behringer generally gets things done.)

The part that I'm wondering about now - this should only have affected the WA6SE. There wasn't anything audible on the A90, right?

Everything else is silent

 

[xevman]

Ok guys went to my local electronics shop and purchased a galvanic isolator. This seems to be of decent quality with a metal case and good connectors. I grounded everything hooked it up and line and the problem is solved. What surprised me is before with the grounds lifted there was still a hiss at high volumes (much higher than I would normally listen at) and I just assumed that it was the amplifiers noise floor given its a tube amp. This hiss is gone now too..... So I assume there was another grounding issue with the USB ground of the DAC causing that noise. Either way very happy with the results and for the price these are a no brainer for unbalanced connections.

 

[MechEngVic]

When a component doesn't share negative interconnect ground with chassis ground, you can get ground loops. The ground should be a solid connection between the wall outlet, the component chassis, and the ground of the interconnects. Improper internal grounding of a component allows current to pass through the negative of the interconnect. Sometimes a simple wire connected to the chassis of both components eliminates the loop. That's why many (mostly older) components have a ground connection on the chassis.

 

[mhardy6647]

When a component doesn't share negative interconnect ground with chassis ground, you can get ground loops. The ground should be a solid connection between the wall outlet, the component chassis, and the ground of the interconnects. Improper internal grounding of a component allows current to pass through the negative of the interconnect. Sometimes a simple wire connected to the chassis of both components eliminates the loop. That's why many (mostly older) components have a ground connection on the chassis.

... and then there those of us who keep a bag of clip leads handy in the hifi lair at all times.

DSC_7255 (2) by Mark Hardy, on Flickr
Sorry, I don't have a photo of ground loop troubleshooting, so this elegant crossover design will have to do as an illustration.

 

[dougi]

Ok guys went to my local electronics shop and purchased a galvanic isolator. This seems to be of decent quality with a metal case and good connectors. I grounded everything hooked it up and line and the problem is solved. What surprised me is before with the grounds lifted there was still a hiss at high volumes (much higher than I would normally listen at) and I just assumed that it was the amplifiers noise floor given its a tube amp. This hiss is gone now too..... So I assume there was another grounding issue with the USB ground of the DAC causing that noise. Either way very happy with the results and for the price these are a no brainer for unbalanced connections.

I have used this myself but it does add some distortion, like most transformers will. Likely not audible though. Mine was in a measurement application, so I did pick it up.

 

[Matias]

Secondly is there a safe long term solution I can possibly try rather than doing this cheat method and lifting the ground? I'm going to pack up and disconnect the amp until I know that there is a long term safe fix for this issue which I can try.

Any help advice or insight would be greatly appreciated...

I would lift the ground of the tube amp and keep the ground on the DAC. As you measured yourself, they are connected, so it's not like the amp is missing ground, the problem is too many ground paths. Ever noticed that AVRs don't have ground pin on the IEC inlet?

 

[Atanasi]

I would lift the ground of the tube amp and keep the ground on the DAC. As you measured yourself, they are connected, so it's not like the amp is missing ground, the problem is too many ground paths. Ever noticed that AVRs don't have ground pin on the IEC inlet?

If devices are designed for safety ground, a ground connection through RCA doesn't suit the safety function, so it's not recommended. An electrical shock would be propagated by the audio cable shell, which is not designed for it.

 

[xevman]

I have used this myself but it does add some distortion, like most transformers will. Likely not audible though. Mine was in a measurement application, so I did pick it up.

Interesting to note has anyone here ever measured a isolation transformer and posted the results? The Woo has 2 inputs and a switcher on the back so maybe I can do an A/B test to see if there is an audible difference between running it in the signal path and not. But as you said I doubt it's audible...

 

[xevman]

I would lift the ground of the tube amp and keep the ground on the DAC. As you measured yourself, they are connected, so it's not like the amp is missing ground, the problem is too many ground paths. Ever noticed that AVRs don't have ground pin on the IEC inlet?

Only problem with that is with it being a tube amp, if someone were to hypothetically unplug the rcas or they get tugged off it loses its ground and when you are dealing with super high dc voltages found in one of these I don't fancy my chances if something was to go wrong and the case went live. My chances of survival are probably better lifting the ground on the a90 and D90. That's the thought process I went through when doing this.

 

[dougi]

Interesting to note has anyone here ever measured a isolation transformer and posted the results? The Woo has 2 inputs and a switcher on the back so maybe I can do an A/B test to see if there is an audible difference between running it in the signal path and not. But as you said I doubt it's audible...

I did measure it (this exact model) but I don't have the results any more). I will try to repeat them.

 

[AnalogSteph]

Interesting to note has anyone here ever measured a isolation transformer and posted the results?

Yes, in fact.

It be noted that one of our members bought a Chinese knockoff of the HD400 and was sorely missing the low end with that; the real deal brought the bass back. Transformer performance will also depend on source impedance; in terms of low-end distortion and extension, usually the lower the better.

 

[xevman]

I did measure it (this exact model) but I don't have the results any more).

I will try to repeat them.

Would be good to see. I'm going to try and acquire a Jensen ISO-MAX CI-2RR which is a very well regarded one. With the input switcher it will be interesting to see if there is any audible difference between the cheap and expensive transformers not to mention with or without the transformer entirely.

 

[dougi]

Measurements of that cheap Digitech isol TF. Rolloff at bass and very high distortion at bass frequencies. 96kHz sampling.

frequency response at +10dBu (2.45V)

THD sweep at +10dBu

THD sweep at 0dBu (0.775V)

THD level sweep at 100 Hz.

These were measured using a RME ADI-2 PRO. Not optimised for S/N in the setup but for comparison loopback at +10dBu single ended is below.