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I am recording guitar direct into a RME fireface UCX using unbalanced cables into the TRS jack. In the manual it says "When using unbalanced cables with TRS jacks: be sure to connect the 'ring' contact of the TRS jack to ground. Otherwise noise may occur, caused by the unconnected negative input of the balanced input."

How is this done?

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    It would be simpler to not use a TRS cable, just use standard TS. – Tetsujin Jan 5 '17 at 7:27
  • Go ahead and ignore this. I thought it meant ts cables with trs INPUTS, it just meant unbalanced cables with trs tips. My bad – Dave Jan 5 '17 at 7:36
  • @Dave you should delete the question if it is longer required. – SaggingRufus Jan 5 '17 at 14:52
  • ARE you getting noise? – Laurence Payne Jan 7 '17 at 14:41
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When you wire a TRS plug to a mono cable, only connecting the shaft to the cable's shield and the tip to the wire,

How a TRS connector should not be wired for use with unbalanced cables and balanced inputs

and plug that in a balanced input, the interface will see the following potentials:

  • Shaft: ground (duh)
  • Tip: (+) signal. Fine so far; if the input were unbalanced this would be all we needed.
  • Ring: undefined! The ring contact is “dangling in the air”, being not connected to anything in the cable. Well, not literally in the air, but it's still basically a short antenna, and if the input impedance is high it may well pick up some noise. Since this is supposed to be the (−) input, this noise will then be audible on the recording (with inverted phase, but that won't make it less annoying). See also the end of my answer for another problem here.

The correct wiring would instead be to link the ring also to the shield:

Making a mono cable out of a TRS plug

  • Shaft: ground
  • Tip: (+) signal
  • Ring: ground

Here, you've shorted any possible antenna pickup agains ground. The negative input now won't have any proper negative signal as it would have in a real balanced connection, but it also won't have any significant noise.

Note that this wiring is essentially just a complicated way to make an off-the-shelf mono cable: a normal guitar cable has no ring, that contact is simply part of the shaft and thus anyway connected to ground.

How a TS plug has that wiring “built in”



Incidentally, there's also a third wiring that would be completely wrong for a balanced input: if both tip and ring connect to the wire

Ring and tip connected

you get

  • Shaft: ground
  • Tip: (+) signal
  • Ring: (+) signal

Now what the balanced input will do is subtract the two (+) signals. Normally this is useful: it cancels out interference picked up in the cable. In this case however, it would cancel out the signal you're trying to record!

This phenomenon is more typically encountered when plugging a headphone output with a stereo cable in a balanced mono input: the two stereo channels carry more or less the same signal (at least for central components like main vocals, bass and drums), so the balanced input will only accept a strange hollow reverbey side signal.

And in fact that's a possible problem with the “undefined ring” wiring, too: while the ring is still pretty well shielded from outside interference, it can easily couple capacitively to the (+) signal, i.e. even if it's not properly connected to the signal wire it may cause some signal-cancelling. This is especially an issue if the whole cable is stereo, but the ring signal undefined at the other end: in this case there's a considerable coupling capacitance between the wires.


tl;dr: if you feed a balanced input with an unbalanced signal, just use an ordinary all-mono cable (i.e. a standard guitar cable, with TS instead of TRS plugs).

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In TRS format (Tip Ring Sleeve) The tip is positive and the ring is negative and the sleeve is ground. A TS (Which is what a guitar cable is) only has the two wires in it so the ground has to go on the negative wire which is the sleeve of the jack. Inside the female jack on the interface it has three pins that come down and a clip peace. The clip grabs the tip on the little dip on the top of the jack. The next pin just lightly touches the ring and on the inside round part of the opening is metal that touches the sleeve part that is connected to the chassis and the chassis is connected to the ground pin on your outlet. So basically the manual is telling you to not to connect the ground to the tip of the jack because then it will never make it to the ground. Edit- also if you are using a trs and the negative terminal is not grounded and left open it acts as an antenna that could pick up noise from any electo magnetic field around like power cords or even a guitar amp.* (Thank to leftaroundabout for pointing out I didn't answer the question fully) If your guitar is not grounded it may cause some noise but not always.

But you shouldn't have to worry about this because cables you buy from a guitar shop are wired correctly. When you do need to worry is when you are wiring your own guitar cords or wiring a guitar jack. When doing these just make sure you double check you connections and if you not sure just check an online chart. Although it easy to tell when you have done it wrong because the guitar in an amp will probably buzz a lot.

  • “telling you to not to connect the ground to the tip of the jack because then it will never make it to the ground” that is quite certainly not what the manual is saying – why would anybody connect the tip to ground? – leftaroundabout Jan 8 '17 at 0:43
  • @leftaroundabout Sorry I didn't answer the question fully my edits should have fixed that confusion. The reason I said not to connect the ground to positive is because not everyone knows that kinda stuff. It's obvious to people like us but some may not understand yet. Yes "Why would you ever connect the ground to the positive" is dumb but some people may not know. – Braden Larsen Jan 8 '17 at 17:51

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