Modwheel 10k problem

[besh]

Hi, if got some modwheels on my midibox which are only using 40% of a 10k pot.

so I got a very limited range of value. Some say use a 30k pot to increase the value,

but I havent seen any to buy. Some say there is a solution by modifying the MIDIBox ASM file.

Whats the way to go? Anyone already solved this issue?

[julienvoirin]

IMHO you have only 40% because it doesn't use the 280° of the rotation. I noticed on my Moog that the modwheel goes from 4 o'clock to 8 o'clock on the pot.

the best is to use 10bits and some algorithmic ( x+ (pot value>> 2 )for example) in order to get a value between 0 and 127.

[Wilba]

A 30K pot won't help, since you're using the pot as a voltage divider, the range would still be 1.5V - 3.5V (assuming 0V-5V, 40% range at middle).... I'm guessing, you might have one that is only the starting 40% so the voltage is 0V - 2V.

Converting 40% of a 10 bit value into 7 bits would work, but you'd be bypassing the built-in jitter handling. It's much better to use 0V-5V inputs into the Core.

You could try shifting and amplifying the voltage, but that would involve opamps. I'm not the best person to explain how that would be done... but in theory you could do it with a rail-to-rail opamp... assuming the middle of the range is 2.5V, it could amplify 1.5V-3.5V to 0V-5V.

You could also try modifying the pot so the full range of resistance is only in the middle 40%. That would involve opening the pot and "shorting" the resistant strip at each end... you could use a silver conductive pen (eg. this: http://www.amazon.com/CircuitWriterTM-Precision-Pen-silver-based-grams/dp/B0002BBVQO ). You would have to carefully measure the pot's resistance at the ends of the modwheel's range, then with a multimeter, work out where that corresponds on the resistant strip, and "paint" from those points to the ends of the strip. Again I'm assuming it's the middle 40%, if it's only the starting 40%, you only need to paint one end.

[julienvoirin]

You could try shifting and amplifying the voltage

that's why there is a TL072 and resistor inside the Pitch/Modwheel box of the Voyager ... now i am less dumb

[besh]

Thanks for you're help, I think the best solution would be going with a rail-to-rail opamp. But I'm a dummy when it comes to electricity.

Do anyone have a shematic for such a thing?

[nILS]

Gain = 1 + R2 / R1

[besh]

so I got some mc1458P to do it. This thing has 8 connectors

1 1out

2 1in-

3 1in+

4 Vcc-

5 2in+

6 2in-

7 2out

8 VCC+

Is it right that this thing don't need a own power supplie? (vss+ & vss-)

So I connect pin 2 to ground (with the 2 resistors)

the outcoming voltage from pot to pin 3

and pin 1 to ain module

Edited October 1, 2010 by besh

[julienvoirin]

lol it is Vcc+ and Vcc-

[nILS]

so I got some mc1458P to do it. This thing has 8 connectors

1 1out

2 1in-

3 1in+

4 Vcc-

8 VCC+

Those are the relevant pins for you.

It does need power. Vcc- needs to be tied to ground and Vcc+ needs to be tied to +5V.

Unless I am completely blind, that's not a rail-to-rail opamp. The circuit will still "work" but not improve the situation at all, since the voltage will be clipped @ roughly 1V and 4V.

You want something like an OPA347.

[besh]

Another question. With this formula V = 1 + R2 / R1

I get the resistor values. So in my case I need V=3,125.

I tried it with R2 22k and R1 10k and it doesn't work.

Are these resistors to high?

[nILS]

22k/10k are good.

nd it doesn't work.

That's really not helpful. What doesn't work, how do you know it doesn't work, show a schem, some photos, something.

Like I said before, that opamp will not solve the problem.

[besh]

ok I made it.

Pin 2 and 4 to ground

Pin 7 to 5 Volt

Pin 3 is the signal from pot

Pin 6 is the amplified signal to ainx module

to get a doepfer modwheel work full range you need

R1 10k

R2 22k

thanks for you're help.

Edited October 9, 2010 by besh

[nILS]

Glad you got it to work :)