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It seems complicated to connect a digital piano's headphone output to a monitor speaker which takes a "balanced" input. How is it done?

It seems what a "balanced input" is, is to use 3 wires to send a signal, so that no matter how long the cable is (such as 25 feet), the noise can be canceled out. Some info here, here, and here.

So then, if we get one of these speakers, such as the Yamaha HS5 or HS8, then how do we connect a digital piano's headphone output to it? There are TRS to XLR cables that connect Tip and Ring together... but will it work? (because if one signal is subtracted from another, then it becomes 0). If we use the "pure" TRS to TRS or TRS to XLR cables, is it true that it won't work? Or do we need a mixer to do that, because if we do, it may seem like the easiest way is to use a regular computer speaker pair. Also, the cable I use is merely 5 foot long, so it is not like it really needs a "balanced" connection. One possible way a cable can work is, if the ring is totally disconnected, then when the "balanced" signal is obtained, the positive is subtracted from the negative (which is always 0), and we still get the positive signal to output to the speaker. (but so far I have not seen such cable being sold on Amazon). If we connect Tip and Ring, then they subtract to become 0 and should not work. (Amazon does sell cables that connect Tip and Ring together).

The question is, what if we want to connect the digital piano's headphone output to a studio monitor like the Yamaha HS5 with balanced input, how is it done? (and is it a good choice to do that?)

nonopolarity
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    Headphone outs are not well-suited to connecting to line-in, even if you make up a cable to unbalance it. They will be impedance & voltage mis-matched. – Tetsujin Sep 06 '22 at 14:39
  • I tried to provide an answer, but I'd need some more details to be more specific: 1. what piano model (perhaps it has line outputs as well?) 2. Do you want to connect to Yamaha HS5 specifically, or some other speaker? 3. Do you want to use two speakers or only one? It may not be obvious, but digital piano signal is stereo. – user1079505 Sep 06 '22 at 14:57
  • I do have a couple of digital pianos (some are like $200 such as the Casio CT-S1, but this one probably doesn't need an external speaker as it sounds good AS IS)... but my concern is mainly headphone out, because such as the P125, I think it has no Line Out, but just headphone out and headphone out is more universal... also, I am ok for mono for now... as I just want to spend $200 on one HS5... but it makes me wonder if I want stereo, how is the TSR cable going to make it stereo with one cable needing to output to two HS5? – nonopolarity Sep 06 '22 at 15:15

3 Answers3

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  1. Yamaha HS5 has both balanced and unbalanced input, you can simply use the latter.

  2. If you're looking for other devices, some of them have a "combo" inputs, which may seem like XLR at first, but in fact allow also to connect an unbalanced 1/4" jack. Check your device spec sheet.

Combo XLR/jack

  1. I agree, piano headphone or line output should be quite strong and should work fine with an unbalanced connection. Give it a try. The worst thing I can think of are ground loops which may add some noise.

  2. As you wrote with a properly made cable you can connect an unbalanced output to a balanced input, but the connection will be still unbalanced. It might be good enough for you.

  3. For a truly balanced connection you indeed need to convert the signal. You could use a mixer, as you proposed, but a more typical tool for the job is a DI box.

user1079505
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    The jacks on the HS5 are also balanced, TRS… & the 'worst' thing that can happen if you whack a headphone out into a line in without attenuating hard is "bang, there go the cones." – Tetsujin Sep 06 '22 at 14:52
  • @Tetsujin Thanks, I didn't realize. But at least it makes the connection easier, you can just plug an unbalanced TS jack it for an unbalanced connection. – user1079505 Sep 06 '22 at 14:54
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    It will - it will also knock your headphone output by 6dB. I'd still make darn sure you drop the volumes before doing it. It's not something I've ever tried but it just doesn't sound like a good idea to me. [My monitors are 200W each with no input attenuation… not going to plug those into anything at random ;)) – Tetsujin Sep 06 '22 at 14:57
  • yeah, the HS5 specs say it is balanced input, but the product description says it is for balanced and unbalanced input, so confusing. Now, the "Ring" is just 0 type of cable may exist: it is the TS to XLR cable... so the "Ring" is missing and is always 0, therefore when the subtraction is done, we only get one signal. But right now, since HS5 takes unbalanced input, so I will just use TSR to TSR cables and there should be no problem with it – nonopolarity Sep 06 '22 at 15:11
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    Manual has this, for both types - https://i.stack.imgur.com/yDW7r.png - only figure it gives is Input Sensitivity / Impedance: -10 dBu/10k ohms [Manual link](https://jp.yamaha.com/files/download/other_assets/4/793644/hs8i_en_om_c0.pdf) – Tetsujin Sep 06 '22 at 15:22
  • Also, I think this cable works for unbalanced to balanced: get a TSR to TS + TS cable. Then now, plug the TSR into digital piano's headphone out, and feed the TS to the monitor speaker. The speaker takes the positive signal and subtract from the negative, but it is the same as ground, which is 0, so now the speaker just takes the unbalanced signal as if it is balanced and can still play some sound. The same should go for, if the TS is plugged into piano's headphone out, and the TSR is plugged into the monitor speaker – nonopolarity Sep 06 '22 at 15:22
  • @nonopolarity yes, you need a TSR to TS+TS cable like that. If you tried to connect the headphone out to a single HS5 with a TRS-TRS cable, the monitors would subtract left and right channels, which would result in cancellation of big portion of your sound. – user1079505 Sep 06 '22 at 15:25
  • oh my goodness... so I got the wrong cable (again)... I need a TS to TS cable? (or a TSR to TS + TS cable). I thought HS5 can handle unbalanced input AS IS (its built in circuitry can handle that), but no... it is through a hack of "nothing for you to subtract"? It is like the stone age... – nonopolarity Sep 06 '22 at 15:27
  • @nonopolarity yes, but in the headphone output you get "something" to subtract – the right channel in the "ring" – user1079505 Sep 06 '22 at 15:29
  • a bit interesting... it is like "balanced" cable is a better world, but to have backward compatibility, simply use a mono TS to TS cable... so that R is the same as S and nothing for the T to subtract... it is like utf-8 is a more advanced character system, and it is backward compatible with all the ASCII (I think 7 bit ASCII) algorithms we have in the past... – nonopolarity Sep 06 '22 at 15:43
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    @nonopolarity if you plug a TS jack into a TRS balanced mono output you'll get an unbalanced signal. But phone output is unbalanced _stereo_. – user1079505 Sep 06 '22 at 16:41
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If you can convince your keyboard to pan everything hard to the left (namely with the right channel being silent), you get output that is pretty suitable for a balanced input by just using a normal balanced TRS cable (the difference to a stereo cable is subtle: a balanced cable has a defined twist of both signal wires): a balanced input works by interpreting the difference between its two inputs, and the difference to a signal that is zero is just the non-zero signal. How does this differ from an unbalanced connection? For one, the shield is not running signal current. For another, the source impedances of both "signals" are the same since they are from the same headphone circuit.

Some balanced outputs are actually implemented that way (with a matched resistor pair from ground and a low-impedancy output connecting to return and signal wires) while the "proper" way is sending an inverted signal on the return wire. That gives a higher SNR ratio but otherwise is indistinguishable on a balanced input and may get better results on an unbalanced input.

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If the piano is mono, then the signals on the Tip and Ring will be the same.

If you connect either the Tip or Ring to one of the balanced lines, then the Sleeve to both the other balanced line and the ground, then it should work.

Turn the headphone output volume down to a moderate volume to ensure it's not above normal line levels. The most appropriate approach would be to set the speaker to a moderate volume level, then adjust the volume at the headphone output.

Simon B
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