Volume pedal application

[captainate]

Hello friends,

I have a stereo volume pedal I've been using for guitar. It works great, but now I find a need to use it temporarily after the output stage of my MIDI keyboard rig. Ernie ball makes two separate pedals for these purposes, but I'm wondering if purchasing a whole new pedal is necessary. When using the "passive version" (schematic below) with my keyboard system, the taper of the pedal is almost logarithmic in it's perceived response (meaning heel-down is nothing, and still almost nothing until last 10% of travel). No matter how hard I drive the input, the taper is still the same. Why?

The pedal they make for "Active" circuits has a 25k audio pot instead of the 500k linear in mine. What accounts for the difference in response, and is there any way to use the pedal for my needs without modifying it and voiding the warranty (or buying a whole new pedal for $140) Thanks!

"Passive" Stereo Volume Pedal

Active Vs. Passive pedals

 

[alec_t]

1) Is your guitar pickup an active one or passive?
2) Do you have
(a) the pickup output spec (voltage level, impedance) ?
(b) the keyboard output spec?
(c) the amp input spec?

 

[ElectroNewby]

Funny... I'm actually trying to calibrate my FV-500H. I thought I needed to get the 500L but I'm not sure anymore, I got it to work yesterday.

Did you put the volume to minimum ? Do it. It extended my range.

 

[captainate]

alec - It's just a regular strat, no active pickups.

The rig I am using is Logic Pro's Mainstage --> RME FF800 converter/interface --> pedal --> mixing board. I experimented with driving the pedal input in all kinds of ways, like having a really hot input/not much gain on preamps at the board, and the reverse. Is it simply a taper thing? Or is there some impedance factor or something that I'm missing?

 

[alec_t]

I did consider this might be an impedance factor, which is why I asked those questions in post #2. But having run a simulation in LTSpice I think it's more likely a taper thing. Here's my circuit for an experimental adapter to plug into the pedal and which should make your 500k linear pedal resemble a 25k audio taper pedal. The degree of taper can be reduced/increased by increasing/decreasing R3 and R4. With R3 and R4 =68k the taper is quite pronounced; but if R3 and R4 are both, say, 220k there is only a slight taper. By using a dual-gang ~250k pot for R3 and R4 you could have a gig-adjustable taper. The adapter input impedance varies from around 20k with the pedal at minimum to around 27k with the pedal at maximum.