Voodoo Lab

Hello,
Please... can you help me?
I’m using the GCP with two BOSS FV-500L to control expression.
I’ve connected both pedals with TRS (stereo) cable and using the EXP output on the BOSS pedals.
The problem is when i rock both pedals, the MIDI values goes from 0 to 125... and sometimes from 0 to 124... and never reach the maximum value (127)...
When i use it to control whammy, for example, it never reaches the maximum value and the sound is bad...
I even opened both pedals and removed the “minimum volume” pot... to make it as transparent as possible, but it didn’t solve the problem.

Is there any “calibration” i can do on the GCP?
Or it is just a bad pedal?

Another issue i notice is that the values doens’t change a lot in the begining of the sweep... and most of the changes happens in the end of the pedal travel... like it was a logaritmic taper... but in the specification they say it is a 10k linear pot.

Is there any way to get an even sweep??

Thanks a lot,
Wagner.

The main problem of not being able to reach the full data value of 127 is because the 10K potentiometers are a bit too low for the Ground Control Pro and together they are pulling the reference voltage for the expression pedals circuit down too low. You can modify the Ground control Pro to accept these pots by lowering the value of R22 to be about 100Ω. However this will not fix the problem with the feel/taper, you may just want to use something with at least a 25K pot and maybe an audio taper.

I hope that helps!

Hello John,
Thanks for the answer.

Maybe another option is to use the volume pot of the pedal... instead of the exp pot... these pedal have 2 volume pots... and 1 exp pot.

On the BOSS site, i found:

Potentiometer Values
FV-500H:
250K - Volume
10K - EXP

FV-500L:
20K - Volume
10K – EXP

So it will be a 20k... and i think it is logaritmic too.

I’ll give it a try and report back.

Thanks again,
Wagner

Hello John,
I’ve rewired the expression pedals to use the volume potentiometers on both pedals.
Now both pedals are getting the range from 0 to 126... unfortunately it couldn’t get to 127... maybe the 20k volume pot is still a little low.
The taper improved a little bit but it still changing most of the value in the end of the pedals travel.

Thanks again,
Wagner