[LAU] Question about using old Yamaha expression pedal

[Bill Purvis]

On 01/09/2022 09:57, david wrote:
> On 8/31/22 22:31, Will Godfrey wrote:
>> On Thu, 1 Sep 2022 09:33:11 +0200
>> Alexandre DENIS <contact at alexandredenis.net> wrote:
>>
>>> On Wed, 31 Aug 2022 18:06:59 -1000
>>> "David W. Jones" <gnome at hawaii.rr.com> wrote:
>>>
>>>> Will a Yamaha expression pedal work on a non-Yamaha MIDI keyboard? It
>>>> uses a stereo 1/4" plug.
>>>>
>>>> Thanks!
>>> Hi,
>>>
>>> Some expression pedals are wired with the pot on TRS, some others use
>>> RTS (i.e. wiper of the pot either on tip or ring). To make things 
>>> worse,
>>> some use a lienar pot, some others use a log pot.
>>>
>>> AFAIK Yamaha uses RTS wiring. On the other hand, most pedals use TRS.
>>> But in a lot of keyboards, the polarity is either tunable or
>>> auto-detected.
>>>
>>> The only advice is to test the pedal on the keyboard, or to check in
>>> its documentation.
>>>
>>> -a.
>> For this sort of thing, and testing leads, PSU polarity etc. a small 
>> cheap
>> meter is invaluable. Takes all the guesswork out of it - so you see 
>> what you
>> *actually* have, not what it says it has!
>>
>>
> I have a meter. Will just have to figure out how to test this using it!
David,
crude ASCII sketch of typical TRS pedal:
S    R    T
|    |    |
|    V    |
WWWWWWWWWWW

A RTS pedal simply re-labels R and T.

Set the pedal mid-way, set meter to KOhms, measure resistance between 
sleeve and ring, sleeve and tip.
You should find one if about half of the other (if a log pot it may be 
way off half, but at least less
than.) The lower reading is the slider. Either way, the best way to test 
is to simply try it.

Bill

-- 
+----------------------------------------+
| Bill Purvis                            |
| email: bill at billp.org                  |
+----------------------------------------+