Some questions regarding ground

Antimon · Posted: Sun Oct 11, 2009 1:54 pm Post subject: Some questions regarding ground

Blue Hell mentioned in a topic regarding patch cables that it makes sense to only connect the tip of 1/4" jacks when using them as patch cables on a modular. This to prevent ground loops (I interpret this to be connections between the ground nodes of modules other than via the power supply).

What kind of nasty effects can you get from ground loops? Hum or worse? I'm currently using a mixture of bi- and uniwired patch cables (haven't made enough uniwires yet). Are you more prone to nasty ground loops if you make many extra ground connections or just one between two modules?

I'm also wondering if all devices with multiple out- or inputs use this technique with common ground for all connections. Case in point: I'm using my MOTU Ultralite to send several CVs to the modulars. Will it be enough to just make one of these connections with a biwired cable (thus establishing a common ground level), or should I use two wires for all connections between the Ultralite and the modular? Might there be risk of ground loop if the reverse is the case?

I've already patched a lot and it all seems to work nicely (no hum at least), but it's always nice to have the theory straight for future issues.

/Stefan

Blue Hell · Posted: Mon Oct 12, 2009 11:13 am Post subject:

The wikipedia article about ground loops seems ok in explaining how ground loops can cause hum in audio circuits.

For patching a modular synth this is a bit academic considering the large signals being involved ... but on my old formant I did use a mix from unshielded cables, shielded cables with shield connected only at one side and yet other cables would be shield connected on both sides ... thing is it's way easier to make unshielded patch cables and way easier to buy cables having a ground connection on both sides.

Antimon · Posted: Mon Oct 12, 2009 11:27 am Post subject:

Ah wikipedia, of course. Thanks!

/Stefan

Ricko · Posted: Mon Oct 12, 2009 4:21 pm Post subject:

In theory you could also just have a low value resistor (eg 470 ohm?) on the 0v/ground line of the cable. That can be enough to dissuade oscillations from loops.

It certainly works for loops for stereos. (I have this at the moment on my CD player for example; it worked a treat.)

When I played in bands we always had a stop of earth lifting power adapters, with the third pin removed (obviously not a US issue). If we had hum in our systems we would try the adaptor. Always worked.

Antimon · Posted: Tue Oct 13, 2009 1:14 am Post subject:

Thanks for the resistor tip. Nice to know if I run into problems later on.

/Stefan

Sound · Joined: Jun 06, 2006 Posts: 842 Audio files: 1