...that there are MANY opinions on carrying the ground wire in a cable. I am wondering about advice any here could give me, or even opinions for that matter...
...I have both balanced AND unbalanced gear in my patchbays.
Some people say only tie all the Input jacks to ground, others say only the output jacks to ground... ( In the cable I mean, as in break the screen on the other jack) Currently I have both input and output jacks tied to ground and it does OK, but sometimes there are anomalies.
If I untie the unbalanced stuff, will it still work?
It depends a bit on what kind of wiring you have and how the signals conductors are connected - if you have screened twisted pair "balanced" cable and the signal is running on the pair then dropping the screen at one end should not be a problem.
I generally wire studios as if everything were balanced... so I use wire and cabling with shielded twisted pairs. In a shielded/twisted pair you will have two "signal" wires. One of these is the "hot" or "high" and the other is the "cold" or "low". These are the only wires that always have to be connected at both ends. The shield is often some copper braid or maybe foil that wraps around two signal wires along the length of the cable - the twisted pair. The shield is a conductor, in the sense that it CAN conduct from one end of a cable to the other end, but it is not meant to conduct current anywhere. In most cables there is a wire running with the shield called the "drain" wire. The drain wire is also called a ground wire but that description is really going in the wrong direction... for the shield to work it has to have a low impedance connection to ground via a drain wire. The shield needs to have one such connection. Multiple connections can cause problems and I can describe these but I want to try and keep this post brief so maybe in a follow-up I will explain how differing ground potentials and ground loops can ruin your day. You CAN wire a studio with twisted pair wire and NO shields connected anywhere and it will work - probably not well enough to use but it will work functionally.
So let's talk about the twisted pair first and leave the shield for a moment.
The hot wire is pretty easy assuming you know how the gear itself is done. The hot wire is going to be THE signal wire in all unbalanced connections so that would be the "tip" connection in most cases except for those insert jacks that have the send and return hots on the same Tip/Ring/Sleeve connector. With XLR connections we now have a standard where pin 2 is hot but enough gear already exists with pin 3 hot that it is always good to KNOW what it what. Some people seem to think that the existence of a standard will somehow metamorphise older non-compliant equipment into agreement but this is not the case and not every manufacturer making gear today follows the "pin 2 hot" standard - so you have to figure that out on a piece by piece basis.
The cold wire is a little less obvious because it is carrying the "low side" of a balanced connection or the "signal common" of an unbalanced connection. Unbalanced signal common is pretty much GROUND. So... in a studio with mixed balanced and unbalanced connections you will often see the low side of balanced outputs being connected to ground at the inputs of unbalanced devices. It turns out that this works but depending on the type and how well the balanced outputs are designed there may be some bad side-effects - these have to be dealt with on a case by case basis - I use transformers. You can also see the unbalanced signal common being connected to the low side of balanced inputs and once again this works - but some gear with active balanced inputs (not transformers) really does not like to be unbalanced this way and sometimes they amplify any noise on the ground wire MORE than the audio signal on the hot wire. This is more a function of the circuit design than the balanced to unbalanced connection in itself and once again these problems have to be taken on a case by case basis - I sometime use transformers or active circuitry to fix this.
The twisted pair or audio pair of wires is how you get a signal from one place to another. Most of the time we have a relatively low impedance source or output being connected through a wire, various connectors, patch bay etc. to a relatively high impedance load or input. One way of looking at this connection is by viewing it as a measurement. The input is essentially measuring an audio voltage as presented at the source terminals (output connector). A voltage is measured as a potential difference between two points. A balanced output would have those two points be the output high and output low whereas the unbalanced output would have those points be the output signal and the output common. Since that unbalanced common is the same as ground and "ground is ground" then you might think that all we would have to connect in an all-unbalanced studio would be hot wires. The problem is that ground is not the same everywhere - the only way that can happen is if all the chassis and conductors carrying ground have ZERO impedance... ZERO. Even a super-conducting wire will have some inductance. So if I want to measure the output of something very accurately and with the least amount of interference I want to measure right at the source - otherwise I will be adding other voltages to my measurement - like ground noise. So two wires for signal - even in an unbalanced situation.
I am zipping though this - there are whole books that cover just this question.
Now - the shield or drain wire, with one very obvious exception, should be connected at one end only. The exception is microphone cables - for two reasons. One is that the shield/drain wire is often the only way the microphone case can be grounded and the other is that phantom power uses the shield/drain wire to carry the return or back to the source - zero volts. With that exception stated it can be said that it is almost universally accepted that the shield/drain wire should be not be used to carry current or be used to ground equipment and that for the purposes of making the shield functional the drain need only be connected at one end. There some "if, ands or buts" regarding this but I'm skipping those as they really don't come in to play often in most studios... maybe in a follow-up.
All the heated talk and controversy seems to revolve around which end gets the shield termination. Connect only at sources or only at destinations? Connect shield/drains at the patchbay and drop at the far ends or drop at the patch and connect at the far ends? There are actually some very good technical papers on this and both sides (source / destination) have been argued. Actually there is some greater advantage in connecting shield/drain wires at inputs to devices as opposed to outputs from devices and here we have to view the patchbay as a device as well. Rather than argue one particular shield religion over another it should be said that the more important thing is to come up with a system that is consistent and does not randomly connect some shields at both ends such that they end up carrying current from one chassis to another or leave some shields randomly unconnected at both ends so they can't do their job. THAT is when problems start happening.
So - a rational shield termination scheme may not solve all your problems. It may be that some chassis are not grounded because all the gear is plugged into "ground lift adaptors"... but this is another topic - power distribution and ground.
For more information, if you really want to know all about wiring AND power distribution, I strongly suggest that you go to http:// and order the reprint of the journal issue on Shields and Ground for $15.00.
) but I'd like to hear all the opinions.
