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From personal experience with the Roland DP at church, I am well aware that you can not "sum" R & L to a mono PA system. On my carry-out boards however, there is only the TRS headphone jack. I have and use a splitter, but 2 questions just arose in my amateur brain, which I am confident 1 or 2 of you can easily answer...Thanks in advance.

---If you plug a TS cable into the TRS out, the ring, which usually carries the right channel of the stereo output, would seem to be grounded to the sleeve. Is this an easy, Left channel only out solution, or is there some electrical mischief created that one should avoid?

---whether DP or Keyboard, the piano voices are probably stereo. What about the other 400 plus voices in the typical (low cost) synthesizer or arranger. If most are mono, it would seem that the phase cancellation issue is moot?

I believe most headphone outputs are short circuit protected, so IMHO it should be fine.

Greg.

Actually, it appears that you should probably be able to use a TRS cable, because a mono receptacle will be compatible with theTRS plug, and leave the ring unconnected: TRS Wiki This has the advantage of not shorting out the right channel.

Greg.

Greg,
Thanks for your search and answers! Amazing what you can find online. So the cleanest way to go from a keyboard TRS out is to use a TRS cable into the TS jack in, for example, a powered PA speaker. I am sure you are correct in that most headphone outs are short-circuit protected--other outs probably less so, but why take a chance. Here, for any other slow learners like me, is the Wiki explanation:

"The results of this physical compatibility are:
If a two-conductor plug of the same size is connected to a three-conductor socket, the result is that the ring (right channel) of the socket is grounded. This property is deliberately used in several applications, see "tip ring sleeve", below. However, grounding one channel may also be dangerous to the equipment if the result is to short circuit the output of the right channel amplifier. In any case, any signal from the right channel is naturally lost.

If a three-conductor plug is connected to a two-conductor socket, normally the result is to leave the ring of the plug unconnected (open circuit). In the days of vacuum tubes this was also potentially dangerous to equipment but most solid state devices tolerate this condition well. A 3-conductor socket could be wired as an unbalanced mono socket to ground the ring in this situation, but the more conventional wiring is to leave the ring unconnected, exactly simulating a mono socket."

The remaining task with this arrangement is to EQ the left channel output to the PA or board to sound best.

Just a clarification: I've heard of phono, I've heard of canon, I've heard of 2.5mm, 3.5mm and 1/4" jack and various DIN plugs. I've even heard of Wonder Plugs and banana plugs, but I've never heard of TRS or TS. What on earth are they?

Tip Ring Sleeve (TRS) they are 1/4" and are used on stereo headphones, stereo inserts, balanced line outs etc. The Tip Sleeve (TS) is your standard 1/4" phono jack for unbalanced mono signals, Guitar, Instrument out/in etc.

Tip, ring sleeve - I'll remember that, now. Thank you Kbeaumont.

The usual way to combine stereo to mono is just to add the channels. If there is something wrong with the phasing at the R and L outputs, it would exist with a stereo PA system too, at least at some listening positions between the speakers. Taking only one of the channels might upset the balance between the bass and treble of a piano sound, if it is separated that way in the source.
I would use a TRS connector and two 10 kohm resistors to merge the two channels. That would combine the signals, and incidentally protect the outputs of the source amplifiers.
In any case, if the amplifiers are shorted together or to ground, that will not cause any problem if it's a line output. Only if it's a power amplifier could there be a problem.

--
Jack

Jack,

My limited experience with (2) DP's into a mono PA is that what you suggest is a mistake--the sound is degraded. There has been a lot of discussion on this issue here and on KC. Most house PA systems are not stereo, while most if not all DP's and keys play back stereo sampled voices. Unless there are true mono samples in the DP/board, the consensus is to pick one channel and then EQ it to correct balance. Imagine trying to EQ only those frequencies which phase cancel in 6 different stereo voices on a Keyboard.