TS plug in a TRS jack?

[Jay Ashworth]

I ought to already know this, but what happens when you plug a mono 1/4 TS plug into a mono 1/4 TRS balanced jack?

Does it *just* unbalance the input? No bad effects on the board? How much does this depend on the board?

 

[jkowtko]

This blog seems to think it could damage the board by shorting out the negative signal:

http://www.broadcastboxes.com/pdf/CircuitWerkes_Generic_TRS_balanced_audio_hookup_info.pdf

I would tend to agree.

However impedance balanced outputs may not have this concern since the negative signal is not a full signal. Someone else will have to comment on this option ...

 

[Chris15]

Balanced input or output?

 

[Jay Ashworth]

Unless I am misreading their posting, they are in the business of selling boxes to solve this "problem". As cynical as it makes me sound, that does make me question the accuracy of their assertion...

 

[Jay Ashworth]

Fair question, Chris. Either I guess.

 

[Chris15]

TS into TRS input will be fine - if it's not, the input simply is not balanced, the differential input by definition needs to be floated from ground, so shouldn't care if it's referenced to "ground"

TS into TRS output has the potential to be a problem.
If it's transformer balanced, it should be problem free, the worst that happens is the transformer is centre tapped and you drop half the voltage - ie 6dB.
if it's impedance balanced, it should not be a problem - it's only a resistor between sleeve and ground, so shorting it affects nothing.

Now the case when things can go wrong, electronically balanced...
Here you have got an active device driving the sleeve relative to the ground. Shorting it could produce an issue, if, and only if, there is not a sensible source impedance in the design. If it's designed as a 600 ohm balanced output for example, then you've still got 600 ohms even if you short the output. We need to remember that intrinsically there will be shorts in the connection process of a TS / TRS plug, so the designer ought to have considered at least momentary shorts to the output.

There may be the rare occurence where things are a bit different - I have a gut feeling my mental alarm bells are ringing with something around ribbon mics, but for the 99.9% of cases I can think of, the above should pretty much be where it's at.

Clear as mud?

 

[Jay Ashworth]

No, that was actually nice. Thanks.

I am particularly concerned with the issue of trying to get more than one unbalanced stereo aux on an x32. It provides an unbalanced RCA connector for In and Out on auxes five and six to give you a stereo pair. But only the one.

 

[Jay Ashworth]

In the long run, of course, the proper solution is to run 32 digital channels via USB to a PC and run JACK and let it do the routing.

 

[Chris15]

You can get an unbalanced output fairly easily - just use a TRS plug rather than a TS and connect nothing to the ring...
make adapters if needed...

 

[Jay Ashworth]

Fair point. I generally just use RCA to quarter inch adapters which is what prompted the question, but you're right it isn't all that difficult to make up custom cables.

 

[Chris15]

http://www.behringer.com/assets/X32_M_EN.pdf
Refer to the block diagram on p65

The aux outputs 1 through 6 are unbalanced on TSes on the X32 anyway

 

[Jay Ashworth]

I had read the manual, and I was pretty sure it said balanced. Lemme see...

 

[Jay Ashworth]

P66: Aux Inputs/Outputs; 1/4" TRS balanced: 6/6

 

[Chris15]

I love documents that are internally inconsistent!

 

[Jay Ashworth]

I actually propose to start helping them with that... no reply from their wiki editor yet.

 

[WooferHound]

I've been plugging TS plugs into TRS inputs and outputs for 40 years and never had a problem with it.

 

[JD]

I've been plugging TS plugs into TRS inputs and outputs for 40 years and never had a problem with it.

Pretty much the same here. Older equipment with real transformers were never a problem. Then, a couple of years ago, lost the output drive on a cheap mixer. When I did the repair I noticed the balanced line was driven active with little protection. Don't have much audio gear (Maybe about 6k of stuff I use with a choir) so I changed my strategy. All the unbalanced 1/4 inch cables I have are TRS with the ring tied to ground with a 1/8 watt 600 ohm resistor. Balanced inputs see it as a ground tie. Balanced outputs are not in danger of a direct short. So far, it's been a good solution.

 

[Oldman]

In my 60 plus years of audio work I have often used TS plugs on balanced outputs with no obvious difficulty. As has been pointed out before, the balanced outputs are generally floating and not ground referenced. I think that some of the concerns are actually related to using a TS plug in a TRS jack that is a stereo output. In that case you are shorting the right output signal to ground which can upset, or even destroy, the output stage of the source. You also are only getting the left channel single which can create some interesting effects, especially with sources that are "engineered" with different signals directed to one or the other of the channels. If the source material is recorded as a live recording in a room with everyone in the same room, the effects will be less of a problem since both channels will have both L and R signals present although the balance will be fouled up. I think that John's solution sounds like a good compromise.

 

[FMEng]

As has been pointed out before, the balanced outputs are generally floating and not ground referenced.

I'm afraid that's not true. I have studied the schematics of countless pieces of pro audio gear. Nearly all balanced output stages are ground referenced. The most common arrangement is a pair of op-amps stages, one inverting, and one non-inverting. Most manufacturers wisely put a build out resistor on each output to raise the source impedance, and the op-amps have internal current limiting, so that shorting the output doesn't destroy the device. However, it does put excess amounts of current onto ground traces, which may come back to bite as crosstalk somewhere else in the system.