Building volume pedal from OLD Cry-Baby - Best linear pot for fit?

[shaneo]

Hi all -

I'm a total noob, so be gentle.

I found an old Cry-Baby pedal I'd bought used 40 years ago. The pot seems too dirty to be effective as a wah anymore, and if I have to switch pots, I'd rather set this up as a volume pedal with a close-to-if-not-exactly linear sweep (for lap/pedal steel and dobro).

I've tried to read as much here as possible, but I'm still not confident about several aspects:

• It seems like a 250K linear pot is what I need. Is that going to work for both passive pickups (lap/pedal steels) and pre-amped piezos (dobro)?
• If I use the existing tooth/gear mechanism, it seems I'll only get about 1/3rd of the pot's sweep. If this is true, are there pots with a narrower sweep range?
• Am I pursuing an achievable goal here? Is one volume pedal going to work for both applications? Is there something I don't know or haven't mentioned that could/will significantly impact this project?

I'm also planning to add a 9V jack to this currently-battery-only pedal. Anything I should be thinking about there? Any recommendations on where to source the components?

Thanks in advance -

Shane O.

[stallik]

Welcome.

You are correct that a wah pedal is only capable of rotating a pot for part of its maximum rotation. That means that you can't achieve 0% rotatation as well as 100% or 100% as well as 0%. You have to make a choice when you set the position of the pot shaft against the actuating cog.

To maximise the amount of volume variation, you will find that a log pot is better than linear.

If you're just using the pot on its own, you do not need any kind of power supply however, in order to achieve a better range of volume settings from the less than optimum pot rotation, some people choose to incorporate some kind of booster circuit and use the 'wah' mounted pot to control the output of this. In such cases, the circuit will need a power supply

[amptramp]

There used to be a number of logarithmic pots that had a tap for loudness control components.  Maybe by using the tap as the input, you can make more use of the limited rotational range.  If you want 250 K, you could start with a 500 K pot with a tap and not use the upper end of the volume control (other than maybe connecting the top of the pot to the tap to protect against noise from dust on the track).

[FiveseveN]

An active circuit (inverting op amp) would allow a full range from unity (and boost if required) to mute regardless of the pot's limited travel, as long as it can go down to minimum.

[Mark Hammer]

Craig Anderton's "Volume Pedal Retrofit" seems a good candidate for this.  I probably needs to be updated to use an LM13700/13600, unless you have a spare CA3080 sitting around.  But it's chief virtue is that the pot movement is smoothed out via a cap, making it essentially "scratch-free".

https://www.diystompboxes.com/smfforum/index.php?topic=102065.0

[RickL]

Or you could replace the pot with any of the available replacement pots and use a spst switch to lift the 4.7 uF cap's connection to ground which will turn it into a volume pedal. That way you can still use it as a wah if you want.

This assumes that it is still working as a wah of course, that the only problem is a dirty pot.