Can I measure ground loop potential? Optical cables?


#1

Background: should I spend time and money searching for a high-bandwidth optical cable?

Assumption: There is a gound loop potential between components and that is bad for sound quality.

Question: Can I measure this potential to even see if it is an issue in my system?

I have a nice Fluke multimeter… I suspect I can disconnect cable hookups between two devices, and then simply measure any DC potential between the two units by touching the Fluke leads to say, the ground rings on RCA female jacks. If this will measure potential, then:

  • DC only or AC too? Which is the baddie for sound?
  • What is an OK potential? 0 only?
  • What potential becomes audible and therefore worthy of isolating the units via an optical cable
  • Should all my components be plugged into the same AC house circuit? Does this matter? (FYI, I have all my equipement plugged into a dedicated 20amp household circuit I wired myself, board to outlet, for audio.)

FYI: this is what hapens when you listen to your old Black Sabbath CDs and drink too many Pilsner Urquells… you are influenced by the dark arts…

Peace,
Bruce in Philly


#2

If you are going to use the TOSLink connection, it’s bandwidth is only designed to be up to 96k, but with better quality plastic or reasonable quality glass you may get 176.4k or 192k. You don’t need to spend a fortune, but get something better than came with your last video recorder (VCR, etc.) (I was mildly surprised at one time to find that a $7 cable from Fry’s sounded better to me than some $1000 cables my local dealer talked me into trying… I probably woundn’t have sprung for them anyway, but it was interesting to compare. YMMV.)

Some people have found it worth it to use optical connections in their Ethernet connection, just make sure the power supplies you use on the added Ethernet to optical and optical to Ethernet modules aren’t simple switching supply based wall warts.

All of your components should be on the same “phase” of your house’s mains. Around here that means that they should all be on the same side of your breaker box. One of the best things I did for my audio system in my old house and again in our newer house was to get dedicated circuits for my audio system installed. When doing that you can tie all of the grounds together closer than the breaker box and shrink the groundloops.

You might find a DC offset which causes a groundloop to continuously conduct, but remember any closed electrical loop has a current proportional to the flux thru the loop (which in turn is directly affected by it’s area.) If you have a problem ground loop make it’s area as small as possible to minimize the RF reception (or transmission.)

If the induced current loop has a complex spectrum you won’t really see the whole of it on a simple meter.

Perhaps an easier way to test for groundloop issues is to get a low impedance wire (e.g. say 16 gauge or better) and see if using it to connect various components to a good ground or perhaps to your amp makes a noticeable difference in sound quality. After you find the problem loops (if any) you can figure out how to mitigate or remove them.


#3

Not sure where you are located Ted, but my breaker panel in Michigan is set up with the breakers on one physical side of the box with alternating phases. To say it another way, all the breakers on the left side of the box are odd numbered; 1, 3, 5, 7, etc. But 1, 5, 9, etc. are one phase and 3, 7, 11, etc. are the other phase. I know this since I happened to actually look at the tag where you write in your circuit name for each breaker. There was a diagram showing this. I was always a little perplexed on how a 240 volt breaker (for dryer, range, water heater) would work with two of the same phase. This explains it!


#4

You are right, I was thinking of what it looks like with the cover off and then (at least here) you can see the two phases clearly with the busses down one side or the other. Sorry about that.


#5

Any thoughts on the Synergistic research ground block? Here you connect unused input/outputs from the DAC/pre/amp.


#6

Their technical descriptions are as bad as always: (“The term ‘ground’ refers to a connection to the Earth, which acts as a reservoir of charge.” :slight_smile: ) But I’ve heard the difference a similar device makes. I think you could get the equivalent by getting some similar sized ground conductors, star grounding your system and (possibly) grounding that firmly to the outlets you use. You could probably make a better ground connection to most units with a separate ground wire connected to an appropriate place, but using the unused connectors is certainly easier to do and to explain.


#7

What Ted is referring to is bonding and it is very common in studios to reduce ground loops. For a proper star ground make sure all of the grounding wires are the same gauge and length and that they have very solid connections to your individual units. It takes some effort but is much cheaper than the “ground box” doodads.


#8

I just measured the potential between my Mutec 1.2 and my DSJ… my hookup is usually PC-USB-Mutec1.2-XLR-DSJ (I play around with the hookups).

So I unhooked all links between the Mutec and DSJ and measured the potential between them … I got .001 V-DC and .9 mV AC.

Odd, when I measured AC, I touched the leads and the display read like 66 mV and dropped to .9 over about 5 seconds… always did this. I suspect it has something with the way the Fluke Multimeter does its job.

I have a second USB connection from my computer to the DSJ… with it in or not the measurements were the same. I have this connection simply because I am trying various different hookups… I can’t tell the difference in sound with any combo/cable/configuration I tried… I have not tried an Ethernet connection yet… maybe this weekend. Oh, I did try a toslink optical in place of my XLR… no difference.

BTW, with my Mutec, I can hookup XLR, Optical, Coax, and USB all at the same time from my Mutec and flip through the interconnects using the DSJ remote… I can’t tell a difference. The USB DSJ direct to computer is not a simple flip of the DSJ switch, as I need to change the driver in Foobar also. Again, I can’t tell a difference… good job Ted!

Peace
Bruce in Philly