Jump to content


Please note: You can easily log in to MPN using your Facebook account!

Plug 2 TRS pedals into a single TRS jack? (Fantom-0, but applicable to others)


Recommended Posts

Expression pedals and continuous damper pedals both connect via TRS, and can essentially do the same things except that one stays where you leave it and the other springs back to zero. (Allowing for the usual caveats, e.g. that not even all expression pedals do what other expression pedals do, due to how they're wired or the values of their pots.) So let's say assume that you have an expression pedal and a continuous damper pedal that do, individually, behave just as you want them to when you plug them into a keyboard's TRS pedal jack.

 

Can those two pedals be connected to the keyboard at the same time, i.e. using a 1/4" stereo headphone splitter? Will each pedal operated by itself work just as if it were the only pedal connected? Will the value seen by the keyboard simply be the last value generated by whichever pedal you touched last?

Maybe this is the best place for a shameless plug! Our now not-so-new new video at https://youtu.be/3ZRC3b4p4EI is a 40 minute adaptation of T. S. Eliot's "Prufrock" - check it out! And hopefully I'll have something new here this year. ;-)

Link to comment
Share on other sites



It miiiiight work, depending, but not very well if at all. 

 

Some sustain pedals are switches, and some use a potentiometer for continuous sustain pedal. Yamaha and Roland have different wiring schemes, and expression pedals similarly use different wiring schemes between manufacturers. 

 

If you use a continuous sustain pedal, and the pedal just so happens to use the same pinout as your expression pedal, the sustain pedal will still load the circuit. You'd probably have better results with one that is switched rather than continuous, and that again depends on what TRS connection standard is used. 

 

It's impossible to answer this question without knowing exactly which pedals, and exactly which keyboard. And even then, the answer is likely to be theoretical. And if you happen to leave the expression pedal at one extreme or other, it's likely to look like a stuck sustain pedal when the jack is expecting sustain input. 

Link to comment
Share on other sites

Okay, here's the details then!

 

I'm experimenting with the Roland Fantom-07.

 

Two of the pedal jacks are multi-function. They can take 2-contact "sustain pedals" and they can take 3-contact "expression pedals." I'd be using both jacks in the latter mode.

 

Since my initial post, I have confirmed what I hoped/expected, that the Roland DP-10 continuous sustain pedal and their EV5 expression pedal function essentially identically (properly as expression pedals) when plugged into one of those jacks, the only difference being that one springs back to zero and the other stays where I leave it.

 

My desire is to connect both pedals to one jack, and use one pedal or the other depending on whether I want it to stay in place or spring back. For example, I like a pedal to spring back if I'm using it for pitch bend or to simulate aftertouch or as a rotary speed toggle or as a sostenuto pedal... but I want it to stay in place if I'm using it as a mod wheel substitute, maybe to open a filter, or to cross-fade two sounds, etc. The Fantom-0 nicely lets you define what each pedal does independently for each scene. So, on a given synth scene, I might want both of my non-sustain pedals to still be spring-back pedals (maybe for pitch bend and aftertouch), on another I might want one pedal of each kinds (say, for organ expression and rotary speed  toggle). I never want two "expression" pedals, but I sometimes want two "spring-back" pedals (not counting the sustain pedal, which ib the Roland is always a sustain pedal and cannot be defined to do anything else anyway). So the idea here is to have, essentially, a sustain pedal in one jack (fixed), another spring-back pedal in another jack, and in the last jack, I would connect both a regular expression pedal and a spring-back pedal, and I'd use one pedal or the other depending on the function I have assigned to that pedal jack in that scene.

 

I could test this if I had a 1/4" headphone splitter, but if I've got one, I don't know where. ;-) But before going on a hunt or (more likely) ordering one, I figured I'd ask here, to see if there's any reason this definitely wouldn't work!

 

ETA:

 

4 hours ago, OB Dave said:

if you happen to leave the expression pedal at one extreme or other, it's likely to look like a stuck sustain pedal when the jack is expecting sustain input. 

 

The pedals don't send anything out except when you move them... e.g. pedal at zero is not constantly sending out zero, it sends out zero once. So my thought is, even when at zero, if the other pedal subsequently sent something greater than zero, it would see that for what it is. BUT... If the expression pedal were left in the 127 position, and you then hit the shared damper pedal, as soon as it moved from its resting location (zero) to anything (let's say 1), the 127 value would drop to 1.

 

One unknown here, related to that, is when calling up a new scene, whether the current position of a pedal is inherited from the previous scene, or if it defaults to some particular starting point when the new scene is invoked, or whether default varies with what the pedal was programmed to do, or if you can program what the starting point for the pedal should be. I guess I should do some more experimenting...

Maybe this is the best place for a shameless plug! Our now not-so-new new video at https://youtu.be/3ZRC3b4p4EI is a 40 minute adaptation of T. S. Eliot's "Prufrock" - check it out! And hopefully I'll have something new here this year. ;-)

Link to comment
Share on other sites

5 hours ago, AnotherScott said:

The pedals don't send anything out except when you move them... e.g. pedal at zero is not constantly sending out zero, it sends out zero once.

 

Ah, but that's not how these pedals work. They don't "send" anything, ever. The pedals present different electrical resistance to the keyboard's jack circuit, and the microprocessor inside the keyboard takes periodic measurements of that resistance. More specifically,  in the case of a the expression pedal, the keyboard supplies both a reference voltage and a ground reference to the ends of the potentiometer, and then measures the voltage at the wiper. This voltage varies depending on the position of the pedal, and the keyboard's internal microprocessor and performs this measurement repeatedly, perhaps ten times per second. So if you don't move the pedal, it's not so much a case of the "pedal not sending anything" but rather, the keyboard doesn't measure any difference in voltage at the wiper so it decides the pedal has not moved. 

 

The sustain pedal does something similar, and you've already determined that your sustain pedal is also a continuous device like the expression pedal. Here's the problem: the expression pedal at its extreme position "looks" exactly like the sustain pedal to the keyboard's periodic measurement. So if you leave the expression pedal in a position that "looks like" sustain down, and you have a piano sound selected that's expecting a sustain pedal, the keyboard will interpret what it's seeing as a sustain pedal held down. It cannot tell the difference. You don't even need a Y-adapter to test this, simply select a piano type voice with the expression pedal plugged in, and try moving the expression pedal while you play. 

Link to comment
Share on other sites

11 hours ago, OB Dave said:

Ah, but that's not how these pedals work. They don't "send" anything, ever. The pedals present different electrical resistance to the keyboard's jack circuit, and the microprocessor inside the keyboard takes periodic measurements of that resistance....perhaps ten times per second.

Very interesting info, Dave, thanks! I hadn't envisioned it being something the keyboard periodically "polls" rather than the pedal "sending" a resistance value when a pot moves. (I put "sending" in quotes this time since I do understand, the pedal being passive, it doesn't literally "send" anything, but I was thinking the keyboard could simply respond to the changed value, without specifically having to periodically poll it, which is what I was calling "sending" a value.) I wonder if the end result may be the same, i.e. that as long as nothing has changed since the last time it was polled, the actual physical positions don't really matter, and similarly, whether the keyboard is periodically "polling" or rather merely "noticing" when something has actually changed doesn't necessarily matter either, because what the keyboard "sees" at any given moment isn't really changing, unless you physically move one of the two pedals.

 

Either way, though, I'm realizing that the value that is being seen by the keyboard could then be the result of the combination of the two pots, which could be different from from the value it would see with just one pot, so it's possible that the whole idea falls apart as soon as you combine the pedals and the keyboard "sees" some value that is determined by the presence of both pots, with that value being inconsistent with the normal values it would see when operating either one of the pedals alone. So it's  not just a matter of things like whether the keyboard would see the greater of the two values, the lesser of the two values or, (what I'd expected/hoped) the most recently changed of the two values, but I see now another possibility, that it continuously sees "combined" values from the two pedals that are inconsistent with any of the desired behaviors from either one of them. So I'm increasingly pessimistic about the odds of this working!

 

ETA: Maybe it would help if I made a point of setting the expression pedal at zero when I was intending to use the spring-back pedal? (Naturally, the spring-back pedal is always at zero when I'm not specifically engaging it.) That way at least the possibility of a "cumulative" value may be addressed by trying to make sure that the unused panel only adds "zero" -- though I don't know that the "zero" setting necessarily equates to zero electrical signal. And maybe the mere presence of the two pots alters the value of what the board is seeing.

 

11 hours ago, OB Dave said:

Here's the problem: the expression pedal at its extreme position "looks" exactly like the sustain pedal to the keyboard's periodic measurement. So if you leave the expression pedal in a position that "looks like" sustain down, and you have a piano sound selected that's expecting a sustain pedal, the keyboard will interpret what it's seeing as a sustain pedal held down. It cannot tell the difference. You don't even need a Y-adapter to test this, simply select a piano type voice with the expression pedal plugged in, and try moving the expression pedal while you play. 

 

I had already confirmed that, without a y-adapter, the expression pedal and the (continuous) damper pedal behave identically (except, obviously, the expression pedal stays where I leave it, and the sustain pedal always returns the expression level to zero when I release it). I had always assumed that the keyboard can't "tell" which pedal I have attached, it's just seeing the value from a pot and has no idea what kind of mechanism is moving it.

Maybe this is the best place for a shameless plug! Our now not-so-new new video at https://youtu.be/3ZRC3b4p4EI is a 40 minute adaptation of T. S. Eliot's "Prufrock" - check it out! And hopefully I'll have something new here this year. ;-)

Link to comment
Share on other sites

On 4/12/2022 at 5:34 AM, AnotherScott said:

I wonder if the end result may be the same, i.e. that as long as nothing has changed since the last time it was polled, the actual physical positions don't really matter, and similarly, whether the keyboard is periodically "polling" or rather merely "noticing" when something has actually changed doesn't necessarily matter either, because what the keyboard "sees" at any given moment isn't really changing, unless you physically move one of the two pedals.

 

It's kind of a combination of the two. The keyboard does poll the pedal input periodically, and then has rules about when to "notice" a change. I say this because there is always some amount of noise on these inputs. A lot of modern keyboards use something like a 10 bit analog to digital converter to read these pedals. So the keyboard "sees" a value between 0 and 1023, but there will be noise on this input. The keyboard might read 412, 413, 412, 413, 412, 413 etc. The keyboard's software will typically have some threshold values so that the value needs to change a certain amount before deciding to interpret that as a pedal move.

 

But in the end, the keyboard is reading a voltage coming back from the pedal, and noticing when the value has changed enough to consider the pedal to have moved. 

 

On 4/12/2022 at 5:34 AM, AnotherScott said:

 

Either way, though, I'm realizing that the value that is being seen by the keyboard could then be the result of the combination of the two pots, which could be different from from the value it would see with just one pot, so it's possible that the whole idea falls apart as soon as you combine the pedals and the keyboard "sees" some value that is determined by the presence of both pots, with that value being inconsistent with the normal values it would see when operating either one of the pedals alone.

 

That's exactly correct. If you were to connect the two pedals via Y-cable, both pedals would be loading the circuit. If the sustain pedal was wired the same, and if it was a switched type instead of a continuous type, AND the pedal switch is open when the sustain pedal is in the up position, it might even work. An open switch isn't going to load the circuit at all. But you would still have the issue of a piano voice thinking the sustain pedal is stuck down, if the volume pedal happened to be in the wrong position. 

 

In the case of a continuous sustain pedal, AND if both pedals are wired the same, hooking the two pedals in parallel would mean having both pedals loading that circuit at once. So moving the volume pedal through its full range might only give you half the volume values, the sustain pedal may not be able to make a big enough voltage swing to be interpreted as pedal-down, and so on.

 

 Hope that made sense. 

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...