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Elka VP-10 pedal - specs?

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Elka VP-10 pedal - specs?

Postby The Elf » Wed Apr 29, 2020 10:49 am

I've just tried to use my Yamaha FC-7 expression pedal with my Elka MK76 - no joy. Sigh...

The MK76 manual specifies their own VP-10 pedal for the job. Does anyone know the spec of the Elka VP-10 pedal, so that I can figure out how to rustle up an alternative?

Essentially I need need to know the Ohmage and connection assignments
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Re: Elka VP-10 pedal - specs?

Postby Hugh Robjohns » Wed Apr 29, 2020 11:25 am

I believe the Elka VP10 is an active LDR-based pedal.

I think the volume socket provides +5V on the ring contact, the sleeve is grounded, and a variable voltage is returned to the tip contact.

Elka VP10.jpg


The Yamaha FC7 also expects the bias voltage on the ring and returns the variable signal control voltage via the tip contact ...

However, the FC7 uses a 10K pot with a 50K trimmer at the bottom of it, whereas the absolute minimum resistance the VP10 can provide is 10k...

So I'm wondering if the base resistance in the FC7 is set too high?
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Re: Elka VP-10 pedal - specs?

Postby The Elf » Wed Apr 29, 2020 11:39 am

Then I suppose the question is... what pedals could I buy that would satisfy the requirements? :D

That looks far more complex engineering in the pedal that the 'pot in a box' I believe most pedals are? And it probably explains why my usually successful 'dance of the crocodile clips' has yielded zero results! :headbang: :lol:
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Re: Elka VP-10 pedal - specs?

Postby The Elf » Wed Apr 29, 2020 11:49 am

I found this:
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Re: Elka VP-10 pedal - specs?

Postby Hugh Robjohns » Wed Apr 29, 2020 12:05 pm

That appears to show the +5V bias voltage on the tip and the CV coming back on the ring... so the opposite way around to the diagram I found!

The optical pedal, using a light-dependent resistor (LDR) was the preferred arrangement in organs back in the day as it was a smoother and quieter solution. Applying a DC voltage across a variable resistor usually resulted in a noisy output.
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Re: Elka VP-10 pedal - specs?

Postby The Elf » Wed Apr 29, 2020 1:18 pm

Could I buy a handful of potentiometers and try them out with a view to fitting them into a old pedal?

If so, what range of values Ohms/lin/log should I try?
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Re: Elka VP-10 pedal - specs?

Postby Hugh Robjohns » Wed Apr 29, 2020 2:24 pm

I'd start with a 100K linear or something like that -- it won't be critical -- attach a voltmeter across the wiper/ground, and then note what range of voltages provide the required level changes. Once you know that you can work out a suitable arrangement.

If that diagram I found is valid, it would appear the minimum value will be at least 10k...
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Re: Elka VP-10 pedal - specs?

Postby The Elf » Wed Apr 29, 2020 6:57 pm

Sounds like this might be beyond me, but I'll see if I can buy a pot to give it a try. As you know, I do get baffled by the electronics! :headbang:
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Re: Elka VP-10 pedal - specs?

Postby The Elf » Wed Apr 29, 2020 10:55 pm

A couple of 100k linear pots are on their way to me. I'll let you know how I get on.
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Re: Elka VP-10 pedal - specs?

Postby The Elf » Wed May 06, 2020 12:33 pm

100k linear pots arrived.

I've tried the crocodile-clip dance, and I've methodically made sure I've tried every combination of the three pins to the three connections of a jack plugged into the pedal socket...

Zilch.

Any ideas for me?
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Re: Elka VP-10 pedal - specs?

Postby Hugh Robjohns » Wed May 06, 2020 12:48 pm

Wow! Really? That does surprise me.

How confident are you that the socket is working? Does it need to be enabled in a menu somewhere?

Have you got a multimeter? Can you check that it's providing the +5V reference voltage?
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Re: Elka VP-10 pedal - specs?

Postby The Elf » Wed May 06, 2020 12:59 pm

Hugh Robjohns wrote:Have you got a multimeter? Can you check that it's providing the +5V reference voltage?
I'm on it...
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Re: Elka VP-10 pedal - specs?

Postby The Elf » Wed May 06, 2020 1:26 pm

I can see roughly 6V between sleeve and tip and a bit less than that (5.5-ish) between ring and tip.

I've also tried both pedal sockets. Both sockets are set to function (one as CC11, the other as CC4). Everything else on this keyboard works, so I have no reason to doubt the pedal inputs.

My test rig:
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Re: Elka VP-10 pedal - specs?

Postby Hugh Robjohns » Wed May 06, 2020 2:01 pm

Hard to tell which croc lead goes where in that photo, but it sounds like the supply is on the tip, so that would go to one end of the pot, sleeve to the other and ring to the wiper...

I'm assuming there's no volts between ring and sleeve?
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Re: Elka VP-10 pedal - specs?

Postby The Elf » Wed May 06, 2020 2:10 pm

Zero Volts between ring and sleeve.
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