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TRS - always suitable for balanced I/O ... or not?

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TRS - always suitable for balanced I/O ... or not?

Postby Eddy Deegan » Tue Feb 04, 2020 10:10 pm

Testing some cables in one of my storage boxes that have TRS jacks I see that some are wired such that each conductor is fully independent whereas others have a shared sleeve between the tip and ring.

Are both these types suitable for use in balanced I/O or should I pick one type in preference to the other?

I suspect this is a perennial question but I've done a few searches and haven't found an obvious (and trustworthy) answer and there seems to be a bit of confusion out there which doesn't help :blush:
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Re: TRS - always suitable for balanced I/O ... or not?

Postby Eddy Deegan » Tue Feb 04, 2020 10:32 pm

I think I may have worded the question wrong (I confess I find this sort of thing quite confusing). Basically, the UCT100 cable tester shows differences between the cables, such that some have conductors that are direct (1-1, 2-2, 3-3), and the others have a different configuration which also lights up the indicator for conductor 3 (which I assumed to be the sleeve) when conductor 1 or 2 is selected.
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Re: TRS - always suitable for balanced I/O ... or not?

Postby Hugh Robjohns » Tue Feb 04, 2020 10:34 pm

A balanced connection normally has three connections: hot, cold, and screen*. So it needs a connector with three electrically separate terminals -- such as XLR, TRS (A-type, B-type, TT etc).

If your cables have the tip and ring shorted together, or the ring and sleeve shorted together, they can't convey a balanced signal.

So... You either need to rewire the connectors (if the cable itself is a two-core+screen type), or replace the cable.

* strictly speaking, the screen connection is only there for electrostatic screening -- it plays no part in conveying the signal -- so some line-level balanced connections omit it entirely (most commonly on patchbay cords).
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Re: TRS - always suitable for balanced I/O ... or not?

Postby Hugh Robjohns » Tue Feb 04, 2020 10:38 pm

Eddy Deegan wrote:...the UCT100 cable tester shows differences between the cables, such that some have conductors that are direct (1-1, 2-2, 3-3), and the others have a different configuration which also lights up the indicator for conductor 3 (which I assumed to be the sleeve) when conductor 1 or 2 is selected.

Yes. A balanced cable will light 1-1, 2-2, 3-3. Three direct, separate connections.

If any two different numbered lights come on together you have a short between terminals somewhere. That might be intentional, or accidental, and it may mean the cable is perfectly serviceable in an unbalanced application, but it can't carry a balanced signal.
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Re: TRS - always suitable for balanced I/O ... or not?

Postby Eddy Deegan » Tue Feb 04, 2020 10:40 pm

Thanks Hugh - good to know separate is the right way. Some of these cables have been stored for many years in bulk in largish boxes and probably got some abuse before that so I think damage is quite likely.

I've already binned dozens of absolute pieces of junk with moulded (and now faulty) jacks and hair-thin conductors that I thought were good deals 10 or 15 years ago when I was buying them 16 at a time for 20 quid or so :lolno:

Those I bought later that have decent quality cable and "proper" jacks I can sort out easily enough, just needed to know the correct configuration. Cheers!
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Re: TRS - always suitable for balanced I/O ... or not?

Postby IAA » Tue Feb 04, 2020 11:22 pm

just needed to know the correct configuration. Cheers!

Me too, I’m reassembling my studio after our move and have much the same problem (as well as a few more :headbang: :headbang: that will be heading the forums way I suspect!)

Cheers Both!

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Re: TRS - always suitable for balanced I/O ... or not?

Postby Sam Spoons » Tue Feb 04, 2020 11:47 pm

Don't forget any that may be 'pseudo balanced' with the screen disconnected at one end, or another wiring scheme. You may not have any of those but, just in case, the relevant wiring info is in this .pdf https://web.archive.org/web/20150814183253/http://www.rane.com/pdf/ranenotes/Sound_System_Interconnection.pdf
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Re: TRS - always suitable for balanced I/O ... or not?

Postby shufflebeat » Tue Feb 04, 2020 11:58 pm

Sorry, Ed, just to clarify - are you testing TRS-TRS only or also TRS-(2x)TS (insert leads)?
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Re: TRS - always suitable for balanced I/O ... or not?

Postby Eddy Deegan » Wed Feb 05, 2020 12:43 am

Sam Spoons wrote:Don't forget any that may be 'pseudo balanced' with the screen disconnected at one end, or another wiring scheme. You may not have any of those but, just in case, the relevant wiring info is in this .pdf https://web.archive.org/web/20150814183253/http://www.rane.com/pdf/ranenotes/Sound_System_Interconnection.pdf

Very useful info in there, thank you. Duly filed for future reference.

shufflebeat wrote:Sorry, Ed, just to clarify - are you testing TRS-TRS only or also TRS-(2x)TS (insert leads)?

Only TRS-TRS... fortunately all my insert leads were bought from a good source and work exactly as expected!
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Re: TRS - always suitable for balanced I/O ... or not?

Postby Smellthevalve » Wed Feb 05, 2020 3:16 am


There’s something wrong with the webpage- I’m only seeing the introduction bit :?:
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Re: TRS - always suitable for balanced I/O ... or not?

Postby Eddy Deegan » Wed Feb 05, 2020 8:42 am

Smellthevalve wrote:

There’s something wrong with the webpage- I’m only seeing the introduction bit :?:

I've put a copy of the PDF here :geek:
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Re: TRS - always suitable for balanced I/O ... or not?

Postby ef37a » Wed Feb 05, 2020 12:23 pm

I thought that the thread was going to mention 'stereo' cables?

Those that have two, independently screened cores but, in the case of jacks, a common screen. These are not quite as good for balanced signals as the cores for those should be as close together as possible and twisted.

The question has been asked if standard, twisted core cables are suitable for stereo signals or will they introduce noticeable crosstalk? Happily most gear these days has low resistance outputs, often only 100 Ohms and so I doubt crosstalk is a problem for sensible cable lengths?

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Re: TRS - always suitable for balanced I/O ... or not?

Postby BigRedX » Wed Feb 05, 2020 3:30 pm

Surely crosstalk is just as much a problem for balanced line as it is for stereo/two channel?
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Re: TRS - always suitable for balanced I/O ... or not?

Postby ef37a » Wed Feb 05, 2020 3:38 pm

BigRedX wrote:Surely crosstalk is just as much a problem for balanced line as it is for stereo/two channel?


No because you don't put left and right down a balanced cable, you need two.

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Re: TRS - always suitable for balanced I/O ... or not?

Postby Eddy Deegan » Wed Feb 05, 2020 3:55 pm

ef37a wrote:I thought that the thread was going to mention 'stereo' cables?
I was careful not to confuse stereo with balanced connections in my original post. I probably would have done when I joined the SOS Forum all that time ago ;-)

Those that have two, independently screened cores but, in the case of jacks, a common screen.

This might be a naive question but ... if there is a common screen between the two cores how does that not short them and mess everything up? Or are you referring to a common screen in the mechanical sense, enclosing both cores rather than them being individually shielded? The latter I can understand, but just checking in case I'm wrong on the former.

Happily most gear these days has low resistance outputs, often only 100 Ohms and so I doubt crosstalk is a problem for sensible cable lengths?

My cables are mercifully short, nothing longer than 5m and the important ones only 2 or 3m.

On a related note though, is it likely to be problematic if (even short) non-balanced cables come close to power cables and extensions? I am forced to do a little of this at present, though I have tried to make them at right angles as much as possible as opposed to running alongside.
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