DIY triple pedal for KA90 (replacement for KAS5), some thoughts


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Hello guys. So I bought a KA90 stage piano. It comes with a sustain switch pedal, but there is also a UNIT PEDAL connector at the bottom of the device for connection to KAS5 stand with triple-pedal combo. It is a 5pin connector, I identified it as JST SM 5pin female connector, so it should mate with JST SM 5pin male connector. I ordered the male connector as well as three universal switch pedals, so my plan is to do some DIY work and connect the three pedals to the UNIT PEDAL connector.

I experimented with a multimer and some wires, so the layout of the 5-pin connector should be

left side of KA90 1---2---3---4---5 right side of KA90
1 - 5 sustain switch
1 - 4 soft switch
1 - 3 sostenuto switch
So pin number 1 is common

BUT pin 2 seems unused, although there is a wire for that pin coming from KAS5, at least in image.
KA90 does not support half-damping, according to the user manual, and nothing happens when I connect pin 2 to any other pin while playing.

I would highly appreciate your thoughts/remarks/comments about the unused pin 2.
Thank you.
 
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Ok, I found in the user manual for ka-90 a short note telling that with kas5 one could have half-damping. And I found out that pin#2 has a 8k pull-up to 3.3V.

So I guess the sustain pedal on KAS5 behaves like KP-1H pedal. Does anybody know or could check what's inside KP-1H? Is there a pot or just two switches?

Thank you
 
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Hello again, I made some progress :)
Let me introduce myself, I learnt piano 30 years ago (was pretty good for the time actually), and then I played in an amateur rock band for a few years and then hardly played for 20 years. Back then I had Yamaha DX 7, and never used MIDI features.

My son started taking his classical piano lessons, and I naively thought that any touch-sensitive keyboard would be OK. So I bought Yamaha PSR-EW410. It is a nice keyboard, 76 big keys, nice sounds etc... The son is doing well technically, but his dynamics is poor. The reason is the keyboard has no hammer action.
So we bought Kurzweil KA-90, white one ;-)

I want to DIY a pedal combo for three reasons: 1. cannot find white KAS5 stand in a reasonable time 2. even if I could, I want to keep the other keyboard so I actually use a two-storey keyboard stand. 3. Would like to save a few bucks, since I am an electrical engineer this is also a matter of pride :)

Back to the business, beside multimeter work I also connected KA90 to my laptop (for the first time, hehe), and observer MIDI control change 64 messages. The conclusion is that KA-90 supports a two-switch half damper not continuous one,, so I guess that's what's inside KAS5. But, for full sustain effect the the both switches need be closed. Pin#5 is half-damper, and decimal value 80 is sent through MIDI if the pin is connected to common. Pin #2 is full damper, but both that pin and pin #5 should be connected to common for full sustain to be achieved and value 127 sent through MIDI.

I guess this is the way KP-1H works as well.

Here is a sketch of wiring as per my conclusions.

1613826943669.png


I think it should be possible to DIY this using three universal pedals (with polarity switch). Once I get all the material, I will start trying in the way the guy here did:


I hope this info will help somebody.
 
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Update on progress:
I could not wait to get everything in stock, and wanted to verify half-damping only, using an OEM universal sustain pedal I had around.
To my disappointment, it does not work since the OEM pedal does not have two SPST switches inside, but a single "dual" SPDT switch. Consequently, there is no "third" state of the pedal available, which is if there are two SPST switches in the pedal. I can only get full sustain.

According to the link I copied in the message above, M-Audio SP-2 actually has two SPST switches, so I will buy that one and try again.

For reference, I paste diagrams of SP-2 (as per link above) and the OEM pedal. If I ever manage to make this work, and you want to reproduce my procedure, you should go for a pedal with the wiring equivalent to SP-2

1613912970695.png


Cheers1
 
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What a disappointment!

I received M-Audio SP-2 today, and it seems they changed their internal mechanics in the course of years, so there is only a SPDT switch in the pedal, not two SPST switches as I expected...

So I am on a quest for a relatively cheap sustain pedal with two SPST's inside (one normally open and one normally closed). Anybody, please let me know if you came across such a pedal recently.

Cheers!
 

happyrat1

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Actually since this is a homebrew project you're undertaking why not take a look at some industrial footswitches?

Far more durable with quality microswitches built into the unit and often designed to be modular so they can be ganged quite nicely.

Gary ;)
 
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Hi Gary, thank you for your input...
I would like to have piano style pedals, but if I fail to achieve it, I would nevertheless go with a solution of the kind you mention. For now, I will hunt for a piano-style pedal with two SPST switches. :)
 
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It's me again :)

I couldn't let it go, and played a bit more, so it turned out that SP-2 pedal has SPDT switch with on1-off-on2 states, so it is suitable for emulating half-sustain ;)

Here is the final schematics, based on the post I copied above from another forum.

1614453188772.png


For the transistor, you could use a general purpose npn transistor, but take into consideration its current gain beta (some places it is written as hFE). To have a reliable half-damping signal when the pedal is half-way pressed, the transistor should be saturated then, and the condition for that is approximately Rcollector >= Rbase / beta. Here, Rbase =1MegaOhm + pullup (10k), and Rcollector = pullup (10k). The pullups I previously reported to be 8k, and that is the resistance between an input and common with KA90 powered off. The resistance between two inputs is 20k with KA90 powered off, so I guess 10k is the actual pullup resistor value. Anyway, 8k and 10k are almost the same in the sense of digital electronics ;-). In my case Rbase / beta = 1.01 MegaOhm / 250 (minimum value for BC337-40 as per datasheet) = 4.04k < 10k , so the condition is satisfied.


For the diode, you could use any small signal diode. If your circuit does not work at first, try a small signal Schottky diode like BAT43 instead.

Now I have everything wired up and working, waiting for the mating connector for KA90 to have the project finished.

I hope this will help somebody :cool:
 

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