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Patchbays and transformer isolation for unbalanced lines?
Old 29th January 2014
  #1
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Patchbays and transformer isolation for unbalanced lines?

OK, massed minds of GS, here's a question that I'd like to throw out there for your thoughts...

In my little music room at home, I have a small rack of keyboards/sound modules, all of which have unbalanced outputs on pairs of 6.35mm (1/4") TS jacks (standard L/R stereo output arrangement). At the moment, these all feed into a stereo line mixer (cable length 2-3m in most cases) which then feeds a pair of balanced line inputs on my main interface (Focusrite LS56).

However, I also have a Yamaha n12 that I still use and I'm thinking of replacing the line mixer with a couple of patch bays so that I can repatch just about anything to just about anywhere on either interface. Now, the line inputs on both interfaces are all on balanced TRS jacks and I'm planning on doing all the corresponding patchbay wiring with balanced lines. However, that has left me pondering what will happen with all those keyboard/module outputs?

Obviously, they're unbalanced so anything that they're patched through to will, essentially, be running unbalanced. That isn't a problem in the current setup, since anywhere that they're connected to at the moment "knows" to treat things as unbalanced when you plug in a TS, rather than TRS, plug. But when the patchbay is in place, the interfaces are going to have TRS plugs in all of their inputs, connected out to the patchbay and the only place where TS plugs will be used is where the keyboards then connect into the patchbay. Again, I still don't think this is a problem, but if anyone can see any possible issues with this arrangement, feel free to shout out at this point.

Anyway...to get to the meat of the matter, I'm also wondering about transformer isolating all of those 2-3m unbalanced runs using something like an Art T8. The idea would be to locate this near to the keyboard rack, running short unbalanced (TS) lines into its inputs and taking "balanced" TRS lines out of it to the patchbay. I've never had much of a problem with hum or ground-loop noise or anything like that, but I figured that something like this wouldn't do any harm and it would at least ensure that all of the physical connections into and out of the patchbay were on "balanced" (3-conductor) lines. OK, so I know that the signals running down there from the keyboards aren't going to be proper (differential) balanced signals, since that isn't what's coming out of them in the first place, but at least there will be the transformer isolation in there where the two-conductor signal crosses over onto three-conductor lines.

Thoughts? Possible issues? Completely bonkers idea or good thinking?

Any reasonable replies gratefully accepted.

(Also, just for info, the patchbays will probably be TRS bays such as Samson S-Patch Plus. I know the arguments/pros/cons of bantam or TT bays, etc. and - for me - the TRS bays make more sense both financially and from a convenience/cabling point of view, so please take that bit as read. There also won't be any phantom going through any of this - any mic lines are going to be patched/cabled separately using only XLRs.)
Old 29th January 2014
  #2
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