Yes, you can certainly connect unbalanced signals/cables to a TRS patch bay, the sleeve will simply have two contact points ISO one.. Maybe something else to consider before getting a patch bay is that you'll need to buy (or much better, make) connecting cables. I soldered a lot of XLR to TRS cables to go from outboard gear - many units only have XLR ins and outs - to the patch bays.
@Arjan P saved me some explaining - thank you.
I'll give a very simplified rundown of the difference and why it matters. It comes down to balanced/unbalanced. All that means is that a balanced signal is a 3-terminal connection with a
differential signal of equal magnitude on 2 wires but the signals are of opposite polarity to each other. The 3rd wire is for a shield to protect the signal on the 2 wires. An unbalanced signal is a 2-terminal connection where the signal it present on 1 wire with a ground return. The ground return is the shield, much like the balanced cable, with the exception that
audio is riding on the shield in the unbalanced cable.
OK, what does that mean? It means that XLR and TRS are both balanced transmission line connectors. The added advantage of this system is that any interference that is radiating the cable tends to be cancelled out due to
common mode rejection, i.e. since the signals on the wire are
positive and
negative (out of polarity), any signal of
equal magnitude on both wires will be cancelled out, leaving only the audio. Stated in a way that musicians can understand,
the noise is "phase cancelled" out. Cables where the 2 wires are
twisted together gain even greater common mode rejection benefits. I always by "twisted shielded pair" wires and preferrable with a foil shield and a "drain wire" for the shield signal ground.
[Positive signals are referred to as "high" and negative signals are referred to as "low"]
One thing that must be taken into consideration is that with a balanced cable, there are 2 signals and a ground wire. One cannot simply connect those 2 signals together (a direct short), nor is it good practice to connect one of those signals to ground (shorting one side of the amplifier to ground).
If you plus a TRS cable into a TS jack, then 1 side of that balanced signal is now shorted to ground. Depending upon the design of the connected circuit, something bad may or may not happen. Some devices will have nomenclature such as "TS or TRS" so you know its been designed for that. In general I avoid that situation by making my own cables. When going from TRS to TS I leave the low terminal floating (there are other uses for that terminal that are beyond the scope of this discussion). When I bought by Tascam monitors I was surprised that the recommended cable was TRS to RCA with one side shorted to ground. I made my own cable and left the low side floating.
Guitar signals do not have the advantage of being balanced and therefore are not noise cancelling.
The best way to convert between balanced and unbalanced signals are to use some kind of a converter device for that purpose.
Headphones are unbalanced because instead of a
differential signal carrying the same audio but with polarity reversed, each wire carries a separate, unbalanced signal between each wire and ground (the shield). That is a 3-terminal connection also, which is sometimes why you will hear people say (inaccurately) that a TSS connector is "stereo" and that a TS connector is "mono."
Console Insert jacks use TRS connectors. Inserting a TRS plug into the Insert jack on a console breaks the "normal" (because the jack is a switching jack) and the jack outputs an unbalanced signal to the cable that is connected to it. That is very much like a headphone cable, but instead of L/R + shield, this special dual cable used 1 wire + shield as a Send to the outboard device, and the other wire + shield as the Return from the outboard device. Your console diagram will give you more information. Typically the wires used are Red + Shield and some other color such as Black or White + Shield. Insert cables have 2 wires connected to the TRS connector. I won't get into it here but there are other cool things you can do with Insert jacks and cables, such as pushing a cable 1/2 in but not breaking the normal.
Hopefully you'll now understand what
@Arjan P means when he says in Post #36:
TS patch bays would IMO be best used for physical TRS mixer inserts (where the signals are usually unbalanced).
There is a very good article on Wikipedia that explains this all very well:
https://en.wikipedia.org/wiki/Balanced_audio
