Patch cables: do they need to be TRS?

[Balog]

I recall reading some comments on here about eliminating ground loops through proper wiring in the connections in the signal path. I can't find the darn link that was posted leading to the paper on the subject, so I thought I'd start a thread that would perhaps be able to answer some of the basic questions people may have about this.

The signal coming from the bass is on a mono (TS) cable. Let's say you are using something other than a combo amp (or a combo with effects/tuner pedal etc in the signal path before the amp). Do the patch cables after the initial stop on the signal path need to be stereo (TRS), and if so how should they be wired? What about if one is using XLR instead of 1/4" plugs? And how does this relate to ground loops? I think I understand the basic idea of ground loops (different gear has different referrences to ground, which can cause phase issues and hum) but I'm still a bit unclear on how it all relates.

[line6man]

TRS cables are for use with balanced signals.
Bass gear is almost never balanced, and if you are using pedals, you have to use TS cables in order for the ring terminal of their inputs to short to ground when you plug in a cable.

Also, balanced/unbalanced is unrelated to ground loops.
Balanced simply means that you have two signals 180 degrees apart. The grounding scheme does not change.

[Balog]

Interesting. So in a pre/power setup where the signal path is bass->mic pre->PA amp->cab, all connections up to the power amp are unbalanced and should use TS connectors?

[throbbinnut]

Use TRS or XLR whenever possible - balanced is better than unbalanced as far as noise is concerned. If your preamp has a balanced output, and your power amp has a balanced input, I'd use that to connect them together, whether they are XLR or TRS. Just don't plug a balanced output into an unbalanced input, or an unbalanced output into a balanced input - if you want to do that, you need to put a "balun" matching transformer in between. And "balun" comes from "balanced-to-unbalanced."

Chris

[throbbinnut]

And just to help clear up the subject of ground loops - if you have multiple ground connections between 2 or more pieces of gear, you can/will have ground loops. When you use an unbalanced signal connectors from, say, a preamp to a power amp, and then both of those pieces of gear have a ground conductor in their power cord, now you have 2 ground connections between those 2 boxes - the signal cable ground and the safety ground going to the power outlet. If you use a balanced signal cable, you can break the actual ground conductor (ground lift switch usually), and the signal will still make it across the + and - conductors of the XLR or TRS. Make sense? XLR and TRS balanced don't use ground as a signal reference - they use "plus" and "minus" referenced to each other. It's insanely cool. And they figured this stuff out in the 20's or earlier. Pretty dang neat.

Chris

[Balog]

Originally Posted by throbbinnut

Use TRS or XLR whenever possible - balanced is better than unbalanced as far as noise is concerned. If your preamp has a balanced output, and your power amp has a balanced input, I'd use that to connect them together, whether they are XLR or TRS. Just don't plug a balanced output into an unbalanced input, or an unbalanced output into a balanced input - if you want to do that, you need to put a "balun" matching transformer in between. And "balun" comes from "balanced-to-unbalanced."

Chris

Is it safe to assume all XLR input/output jacks are balanced then?

And if I run an unbalanced signal into a pre, is the pre converting it to balanced before sending it out?

[throbbinnut]

Originally Posted by Balog

Is it safe to assume all XLR input/output jacks are balanced then?

And if I run an unbalanced signal into a pre, is the pre converting it to balanced before sending it out?

For the most part, XLR or TRS connectors implies that the input/output is balanced. The gear should be labelled as such, though.

If your preamp has an unbalanced input, and it has a balanced output, then yes, it is taking care of making the output signal balanced even though the input signal is not.

Chris

[bongomania]

To clarify though--some rack processors (EQ, compressor, etc.) may have both unbalanced and balanced in/outputs. With those, you can't assume any conversion happens. An unbalanced signal in may depart the "balanced" output as an unbalanced signal.

An XLR or TRS does "imply" balanced, but it does not "guarantee" balanced.

As to which patch cables to use, it depends on the specific pieces of gear being connected! If you have a preamp with an unbalanced line-level output (like a large percentage of bass-specific preamps), then there is no way to connect it in a balanced chain without adding a line-level bal/unbal converter. Frequently the XLR output on a bass preamp is at mic level, good for DI, but useless for driving line-level gear like power amps. Or it may be switchable between mic and line level, but then you have to decide whether you want to be able to use it as your DI out or not.

IOW, make your cabling choices based on what gear you actually need to connect together, NOT based on balanced being "better". Also, for the very short cable lengths typically connecting gear inside a rack case, balanced doesn't actually have lower noise or other benefits. It's really an issue with longer cables.

[billfitzmaurice]

Sound System Interconnection

[rhopper]

Originally Posted by billfitzmaurice

Sound System Interconnection

Good reference!