Ground loop

Kingrex

Well-Known Member
Feb 3, 2019
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I had a frustrating experience. I have hinted at my possibly selling my home. That means I have to get into my basement/garage to finish the space to get a higher sale price. That forces me to decommission the power supply to my stereo. That meant pulling my Torus WM45 and Benjamin panel off the wall. As well as converting my main service loadcenter back to stock.
In doing this I landed a 10 awg NM-B branch into my panel as I would tell any client to do, then brought the circuit to a metal double duplex box in the wall and landed the 2 x duplex with wire nuts like any contractor would do.

Preparing to sell I only wanted to reconnect my vinyl for the interim. I hooked up my rack mount Torus RM20 to the new branch wire and plugged my preamp, monoblocks and phono preamp in. BBBZZZZZzzzzzz.

WTF. I spent 2 solid days doing everything. And I mean everything. And this was an odd fault. The intensity rose and fell with the volume on the preamp, irregardless of the selected source or if the pre was muted. I had up to 60db of hum when the volume was maxed. About 45 db when set to upper listening levels. It even hummed with the pre turned off, but at a slightly different frequency.

I changed the branch wire between Romex 10, 12, MC Cable, Oyaide cable, my twisted cable. I changed duplex, wall boxes or no box at all. I went in and out of Torus or wall or a mix of both. I changed powe cables, interconnect, tubes. I moved equipment around. Cheater plugs. Ground lift switches. In doing so I also ran into additional issues such as if I touched the preamp and moved my hand near the crossover it injected a new very loud feedback. I left no stone I could think of unturned.
I eventually rolled my large transformer back in front of my panel and reattached the original direct wired power stip I made. Still a buzz. AARRGG.

What have I not done. Lets connect everything. Lets put the digital back in. Why additional noise would help, I dont know. Mind you I had tried inserting the RCA from my DAC into its slots in the pre, but, the dac was not plugged into the wall. I was more wondering if noise was getting into open RCA on my pre. I had also tried lashing wires between all my gear. This time I reconnected the DAC and plugged the power cord into the wall. Immediately the noise dropped a lot. I then plugged in the server and booted the system. DEAD QUIET. Not a peep. Back to normal.

I don't have my hear around exactly why this happened. My amps are transformer coupled. That means the signal hot pin is not mechanical connected. It should also be noted now, my phono preamp is a Channel D lino 3.3. Its battery powered. The power cord does not have a ground. Someone else can chime in and explain. I think its something like the signal from the pre was never able to reference ground. Not until the DAC was connected and did that for it.

As a learn for people reading. There are SET owners using transformer coupled SET. If your also using a battery powered phono stage, hum might be from that source not grounding the signal in reference to the amp. I am just speculating. Others may know better.

This may also be a reasoning why ground boxes may help. I find for audio in your electrical supply, a single point ground works very well. But Mesh Grounding is another very effective ground. With a Mesh in a data center, the metal floor and all the racks holding the servers are bonded together with many many jumpers lashing the entire ground plane together. In a sense with your stereo, all your interconnects and power cords are making a Mesh. The addition of a ground box or multiple ground.boxes for signal and chassis may make for a more efficient Mesh that is then attached.to the single point ground bonded to the utility. A fixed reference.for all. A very effective ground scheme overall.

Rex
 
Later, Wiring my basement today.
 
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My first guess would be the preamp has a grounding issue, and connecting the DAC gave the preamp a ground connection that it wanted, via the RCA shield connection. That would also explain why the DAC had to be plugged into the wall in order for the preamp to "get ground". I'm going to guess that when you reconnected and powered on your music server, you did so by also connecting one of its (non-optical) outputs to your DAC.
 
If I understood it right the preamp is floating so that seems a little unlikely it was the culprit itself. It would have to generate a hum independently of the frequency from the AC power.
 
I guess you can't move now:mad:
 
I am told the amp is not bonded to the signal hot on the input. Its a transformer. Not a tube. I was told it is connected somehow to the power so do not lift the ground. The amp signal ground and earth ground are open.

The pre has a lift switch. I don't know what it really does. I have it set where it is most quiet and that gives me 23 ohms between signal ground and ground pin at the duplex.

The DAC is open between the signal ground and earth ground.
 
Certain signal will find a way through even if it is not directly connected where you expect. You can get some pretty bad parasitic ground noise in the right conditions. Transformers for instance are not going to stop 60hz, they are only just not connected to the ground necessarily - as in you can get noise injected somewhere else into the signal that the amp will receive.

Without some what of a schematic/diagram it is a little hard to pin down. I am guessing something on the phono side perhaps is making a loop. Phonos are obviously notoriously known for the issue. But certain carts and tables are too.
 
Hey, its dead quiet now. I have digital and analog and love them both. I have no issues.
I can't draw a schematic because I don't have the schematics of any of the equipment I have. And I don't think any of the manufacturer want them publicized if I did have them publicized. I can only measure the basics.
 
I just meant the pieces and what you know about them, not the internal circuits. A visualization of how the loops are forming for me.
 
I think its more about viewing it as why is just the preamp to amp seen as floating and creating noise.
I believe its about the circuit in the equipment.

I would need to know the ciruit in the preamp and the circuit in the amp to know why its not complete and needs the connection of the DAC to "make it happy". Whatever that means.

I say that as the starting place to find a "ground loop" is put a shorting plug in the amp and listen. If no noise, the amp is sound.

Next is to plug equipment into the amp. I was probably thinking to much about wiring in the wall. The best approach would have been:
Connect the preamp - does it hum. Yes
Connect the DAC direct to amp. Does it hum. No.

I would have spent a lot less time if I did what I would asked a client to do.
I have played this in the past and that is a clean path.

Sometimes your too close to the project to stand back and make an objective analysis. In hind sight, I made that mistake.
 
My EE friend that rebuilt my ARC 610t amps and other things has mentioned grounding issues. In the 610t he found 3 ground loops in each.
He commented, he has almost never worked on audio equipment that didn't have ground loops in the designs. He shakes his head and says it makes no sense it would be designed that way.
 
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My EE friend that rebuilt my ARC 610t amps and other things has mentioned grounding issues. In the 610t he found 3 ground loops in each.
He commented, he has almost never worked on audio equipment that didn't have ground loops in the designs. He shakes his head and says it makes no sense it would be designed that way.
I have a SET amp that has gone to 4 different tech to fix internal ground issues. I have spent $10,000 to resolve the issues. I could have bought a brand new version of the amp for less. The last person with it still in his hands for 6 months says he has it down to 1mv noise. He feels he can get it better, so he still has it.

That is something I will say for Dartzeel. That Dartzeel was the most quiet amp I have ever had. Never an issue. Very good design and built.
 
I applaud your commitment and dedication to this hobby/addiction we have. Good luck.
 
I applaud your commitment and dedication to this hobby/addiction we have. Good luck.
That amp is one of my biggest mistakes to date. I should have sent it back and used Paypal to dispute the transaction. I was pretty new and green at the time I bought it. Ralph with Atmasphere told me to abandon it immediately when I posted about the lemon I received. I did not listen and have paid a very dear price. I hope to god it works correctly when I get it back. It will be nice to have a decent SET 845 amp to listen too. Its a good match for my PAP Trio 15 speakers. It should in essence be a brand new amp as every part has been replaced outside of the chassis. And I mean literally everything. All the iron, every socket, wire, cap, resistor, I think the only stock part left is the power supply circuit board that holds the smoothing caps. All the caps were replaced. I sort of wish I told them to PTP wire it, but I am so financially exhausted with it.
 
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Thanks @Kingrex for sharing your experience with us. It is very informative.
The intensity rose and fell with the volume on the preamp, irregardless of the selected source or if the pre was muted. I had up to 60db of hum when the volume was maxed. About 45 db when set to upper listening levels. It even hummed with the pre turned off, but at a slightly different frequency.
Since loudness of hum increases with volume it’s almost certain that hum is introduced before the preamp. It must be embedded to the signal before the preamp to be amplified by volume control. In your case it is phono stage. I don’t think phono stage is faulty but probably it is not designed to work with amps with floating hot signal pin and/or transformer coupled.
Immediately the noise dropped a lot. I then plugged in the server and booted the system. DEAD QUIET. Not a peep. Back to normal.
I think you nailed the problem already with the comment above. DAC is only helping to ground all components.
 
I only have one question.
Is what you did to fix it NEC Code compliant lol.
it’s great to measure but a grounding issues are soo low in current and voltage I’m not so sure it’s helpful
glad your system is working great now.
 
I have a SET amp that has gone to 4 different tech to fix internal ground issues. I have spent $10,000 to resolve the issues. I could have bought a brand new version of the amp for less. The last person with it still in his hands for 6 months says he has it down to 1mv noise. He feels he can get it better, so he still has it.

That is something I will say for Dartzeel. That Dartzeel was the most quiet amp I have ever had. Never an issue. Very good design and built.
There are plenty of silent or near silent
Audio products
in audio there are trade offs to get a sound at times
I’m guessing but ill
Say the silent ones have a completely isolated psu and case grounding input to output
have you tried any form of iso max inline line level iso devices
I have a set always on hand this allows to figure things out faster
 
I do have one. I think rca to rca
 
They make a combo rca xlr with dip sws.
But look up placement of model.
Models allow at start or end and some anywhere.
Not all the same
also if you shunt inputs and still hear hum line an amp good luck lol
 

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