Another ground loop thread

[SimonSB]

Hi all

Long time lurker, erm.. second time poster

I recently received a Topping E30 DAC from Father Christmas . I really enjoy the functionality, but alas, I am suffering from one - possibly two - stubborn ground loops, the symptoms of which are detailed below:

SETUP:
Old PC > Topping E30 via USB in 'Pure DAC' mode > Audiolab 8000a (integrated amp) > speakers / headphones

SYMPTOMS:
As soon as I plug the Topping in to the amp and plug it in, there is a quiet hum. Nothing is plugged in to the E30. The hum is present regardless of what input is selected on the Topping, and its volume can be attenuated via the Audiolab's preamplifier. It is inaudible except at high volumes so it doesn't affect music playback. I point this out as it may be related to the second ground loop (or it may just be mains noise).

When I plug the topping in to the Computer the hum suddenly becomes much louder, to a point where it affects music listening. This hum is present whichever input I select on the Audiolab and on the E30, though its volume may only be attenuated when the correct input is selected on the Audiolab. When plugged in to the PC, I can also hear other noises, like a high pitched whine when I move the mouse, and some miscellaneous electronic chirping.

WHAT I HAVE ALREADY TRIED AND WHAT I AM CONSIDERING:
All the equipment in question is plugged in to the same power strip. I managed to find a data cable with ferrite beads on it - the power cable is the one that was included in the box. I have tried changing the E30's power supply (currently using one with a plastic ground prong, tried ones with a metal ground prong and also a power bank - none made any difference). I tried plugging the E30's power lead in to my PC, at which point a high pitched whine manifested its self (the ground loop noise was also present but the whine was louder). The only thing that seemed to make a difference was plugging both data and power leads in to an old laptop - which removed the first ground loop leaving me with the aforementioned quieter noise. That laptop is not available for me to use on a regular basis though; I would like to use it with my main (desktop) PC.

I have heard of remedies for these ranging from balanced connectors (out of the question; my amp does not have any balanced inputs) and directional RCA cables (with ground lifted at one side), to extortionately priced USB isolators and USB to coax converters (not ideal as I wish to plug a CD player in to the coaxial input).

If I have omitted any important details about the issue, please let me know.

Thanks in advance
Simon

EDIT:
Forgot to mention the amplifier has a dedicated ground port. Could this present a solution?

 

[sergeauckland]

Hmmm

Firstly, just to make sure, the Audiolab is properly earthed, using a three cored main cable and three pin mains plug.

Having got that out of the way, I take it the Topping has a wall-wart supply, so not earthed. What happens if you take a piece of wire from the Topping's metalwork to the Audiolab's earth point (normally provided for turntables)?

If no difference, or indeed it gets worse, then it's worth trying a ground-break adapter, which is a double-wound transformer that passes audio transparently, but blocks earth paths.

There are several available on-line for a modest sum, which will prove the point (or not). Unfortunately, the ones for a modest sum are not very good, but at least will prove whether you have a ground-loop problem or not.

I don't know where you are based, but I have a very high quality (Sowter) transformer ground-break device I built when I had similar problems with a TV connected to my HiFi. If you're in the UK, I would be happy to lend you the unit just to prove the point.. If it works, then you know you have a ground loop problem that's solved with a decent isolator. If it makes no difference, then you know you don't.

If you're interested, send me a PM.
S.

 

[SimonSB]

A sort of bump-cum-status-update post, probably quite poorly written seeing as I am half-asleep today:

First of all, I realise the best solution is an isolation transformer, but I would rather not employ such a solution - unless it is the only solution - as they are rather expensive and I would rather spend the money on room correction. Anyway, I will proceed to list what I have tried so far:

The ground wire was a good idea but adding one did not change anything. However, what I tried that did change something (as seen on a certain headphone focused rival forum) was that I try pulling the RCA cables out slightly to disconnect the ground shield. After pulling the cables out slightly (and thus, as I understand it, remove the ground connection) the first quiet ground loop was gone - only the second computer related one remained, and its characteristics changed too: the hum's volume could no longer be attenuated. Admittedly I did not check whether I could receive audio through the wire in the aforementioned configuration, I should probably have done that before potentially making myself look stupid on this forum!

I am unaware of exactly how RCA cables are wired - I found lots of conflicting information on the internet; I'd appreciate if someone could clarify it for me as I don't want to spoil mine by tearing them open If anyone knows of a cable construction that removes the ground as I did earlier (assuming what I did still allows audio to pass through) could you please let me know.

My motherboard has a S/PDIF header that could potentially output to a toslink optical port. As this would remove the electrical connection to the DAC I assume it would solve the ground loop, but I'd be worried about this adding jitter. If anyone has any experience with similar cards could you also please notify me.

EDIT:
I was thinking about something like this

Simon

 

[tw99]

A sort of bump-cum-status-update post, probably quite poorly written seeing as I am half-asleep today:

First of all, I realise the best solution is an isolation transformer, but I would rather not employ such a solution - unless it is the only solution - as they are rather expensive and I would rather spend the money on room correction. Anyway, I will proceed to list what I have tried so far:

The ground wire was a good idea but adding one did not change anything. However, what I tried that did change something (as seen on a certain headphone focused rival forum) was that I try pulling the RCA cables out slightly to disconnect the ground shield. After pulling the cables out slightly (and thus, as I understand it, remove the ground connection) the first quiet ground loop was gone - only the second computer related one remained, and its characteristics changed too: the hum's volume could no longer be attenuated. Admittedly I did not check whether I could receive audio through the wire in the aforementioned configuration, I should probably have done that before potentially making myself look stupid on this forum!

I am unaware of exactly how RCA cables are wired - I found lots of conflicting information on the internet; I'd appreciate if someone could clarify it for me as I don't want to spoil mine by tearing them open If anyone knows of a cable construction that removes the ground as I did earlier (assuming what I did still allows audio to pass through) could you please let me know.

My motherboard has a S/PDIF header that could potentially output to a toslink optical port. As this would remove the electrical connection to the DAC I assume it would solve the ground loop, but I'd be worried about this adding jitter. If anyone has any experience with similar cards could you also please notify me.

Simon

Optical will remove the ground loop, and won't have any audible downside.

 

[Speedskater]

Ferrite chokes are for radio frequency noise (above about 1megahertz) problems. They won't have any effect on hum. But some buzzes like from cell-phones are actually radio frequency problems.