I finally saved up enough money and bought a new Yamaha P125 digital piano, and I made the error of plugging the sustain pedal jack into one of the AUX outputs and switched the piano on as I couldn't see the labels from the angle I was looking. Now I am concerned that this could have damaged my piano even though it is functioning properly as of now. Should I be worried that I might have somehow damaged my digital piano ?

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    You've heard of Murphy's Law: If anything can go wrong, it will. The original form is: if it can be connected two ways, and one way is catastrophic, someone will connect it that way. Most everything is 1/4” phone jacks, so they've made sure things won't break like that. Commented Jul 10, 2021 at 14:27

5 Answers 5


No, it shouldn't hurt. The worst thing that could have happened was shortening the AUX output terminals. The voltage on audio outputs is low (or zero if no sound was playing), and at the same time the output resistance in typical audio equipment is perfectly sufficient to limit the resulting current below what could damage anything in the piano.

Making similar "mistake" with a power amplifier output could potentially damage something, but with line-level outputs there is no reason to worry.



Audio Line level outputs have an output impedance of 100Ohm - 600 Ohm and it's perfectly safe to short them. In the worst case you draw maybe 50 mA or so.


Very doubtful it's done any harm. It's not even shorting anything out until it's pressed down - that's how it works. To make sure in your own mind, plug something into that aux out, which can go to an amp etc., and will most likely work fine still.

It's when you plug a figure of eight mains plug into an XLR socket that sparks fly. I know, been there, done that, got a hefty bill ! As you found out, make certain you can see the ports properly before any plugs get inserted !

  • Thank you for the answer. I did depress the pedal after switching the piano on as I thought I had plugged it into the right port. Unfortunately I don't have an amplifier that I can plug in to check where the aux out is working properly. Commented Jul 9, 2021 at 15:09
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    Just an addition. There are two kinds of sustain pedals: opening and closing a circuit. Third party pedals are sometimes switchable, and some keyboards (or at least the Korg Workstations) allow you to switch on the keyboard side as well. Big fun if you start a gig and notice that your pedal is configured wrong.
    – Johannes
    Commented Jul 10, 2021 at 23:32
  • I just went to my cable cupboard and confirmed (without power) that yes, the 2 pin mains plug is a fit for the XLR socket. That's bad, both designers must have gone for the same round fraction of an inch...
    – Rich
    Commented Jul 11, 2021 at 1:49
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    @Johannes - I had to play a whole gig with a wrong pedal. That was tough!
    – Tim
    Commented Jul 11, 2021 at 6:43
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    @Rich - it was one of my Roland 'boards that had the mains and XLR next to each other, and not placed easy to see. I found it quite easy to plug in wrong. Repair was nearly half cost of 'board new... A lot had been recalled, but not mine.
    – Tim
    Commented Jul 11, 2021 at 6:46

Can you perform an experiment to test? Plug in some kind of equipment (amplifier, effect, recording equipment) and see if the output is functioning as normal. That should put your mind at ease.

If you don't have anything suitable to test with, I would still probably assume that a quality product from a reputable manufacturer like Yamaha will include short-circuit protection on line-level outputs so that the pedal wouldn't cause damage even if you depressed the pedal while it was plugged in.


No, it's fine. A sustain pedal is just a switch. It's not going to do anything at all, because it's not applying any voltage to the system.

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    It's not applying voltage, but it could draw current if shorted! Commented Jul 9, 2021 at 14:40
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    There are lots and lots of electronic devices that can be severely damaged by connecting a switch to the wrong part of them. Commented Jul 9, 2021 at 22:39
  • Yeah, like a light socket. But not the AUX out of an electronic keyboard, methinks. Commented Jul 9, 2021 at 22:45
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    Yes, the nature of an AUX out is the other essential piece that makes a complete answer. Since that's missing from the answer itself, I'm not surprised this got downvoted, vs. the other answers which point out why shorting that specific output won't harm it. Commented Jul 11, 2021 at 2:43

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