Roland EV-5 pedal

[Ingo Debus]

Paul Perry wrote:
> 
> Anyone ever use one of these as a pedal to generate cv?
> 
> It's got a stereo plug, with a pot (8.8K) controlled by foot,
> and another pot (50K) on the side as an adjustment.
> As you would expect, the pots are in series, so the wiper arm on
> the 8.8K picks off a voltage, with the range determined by the
> side adjustment pot....
> 
> ****BUT!!!!?? here is the problem, the adjustment pot goes to
> earth, not the pedal pot! So, the output (if you ran 15v into it)
> is 12.8 to 15, at one extreme of adjustment, and 0.5 to 15 at the
> other...
> 
> Does anyone know how this thing is intended to be used? (yeah, I
> could just hack it, but it belongs to a customer so I have to keep
> it intact.
> 
> Well, I can use an op amp & shift to get a range symmetric around zero,
> but I wonder what these things normally plug into? and why like this?

This adjustment pot is also often found at volume pedals, to set
"minimum volume" (or minimum cv in this case). I have a Roland A-80
masterkeyboard, in the user's manual the EV-5 is recommended for it as
cv pedal. It plugs into one of the four "control pedal" jacks. The ring
is the voltage supply (5V) for the pedal and the tip connects to the
pedal's pot wiper. With Yamaha (and other) pedals it's the other way
around. The Roland wiring allows a switch with a mono plug to be
connected to the "control pedal" jack also. The mono plug will short the
power supply then, but it is short-circuit protected. There's a 6.8k
pullup resistor at the input in the keyboard for the switch to work,
that's why the pedal's pot has such a low resistance.

Ingo