newbie volume pedal question

[rogerinIowa]

hey guys-

I want to build a volume pedal using an old crybaby housing, but first I have some questions -
Do I use the standard crybaby wah pot, or is there an actual volume pedal pot? Also,  I want to add an external control knob to set the level of minimum volume when the pedal is rolled all the way off. I am thinking that I could install a small pot ( 10k-25k?) that would be in series with the volume pot, and therefore would control the minimum level of volume...

Am I even on the right track with this minimum volume pot  idea? I know it is possible, as years ago I had a morley volume pedal with this simple feature.

Thanks in advance for any good advice, and please take it easy....I only speak Newbie!!

Roger in Iowa

[Mark Hammer]

First, welcome.

Second, your idea about a second pot to adjust minimum volume or range is appropriate.  This is a feature found on some of the better volume pedals.  I suggest you read the article entitled "The Secret Life of Pots" over at www.geofex.com to leann more about how secondary pots and trimpots can be used to adjust taper and feel.

Third, unless you plan to have a switch that pulls the volume pedal out of circuit, use of the existing pot is not recommended.

For two reasons.

First, think of the pot as essentially a variable "leak" between the hot lead and shield on your cable.  Ideally, when you opt for maximum volume, you would like that leak to be as small as possible.  Pot values on conventional wahs are generally around 100k, which is actually a small enough value that unless you have some very nice buffering ahead of the volume pedal you will notice some tone-sucking or loss of definition.

Part of the the equation here is where you plan on sticking the volume pedal in the sequence of things.  If it is your strict and unswerving intention to stick it at the end of a bunch of pedals and use it to remotely control your amp volume, then 100k may be fine.  If you have no idea where whimsy might encourage you to stick it *today*, then I would recommend a higher pot value such as 500k or even 1meg since larger values like those will still enable a bright crisp sound to be attainable with the pedal volume maxed.  You might also consider the use of a compensating cap (120-220pf between input and wiper) such as is found on Tele's and other Fender guitars to retain highs as the volume is reduced.

The second reason for not using the existing pot is that the taper that is suited to sweeping a wah filter may not be suitable for producing the sort of control over volume you want.  For instance, most of the useful volume changes may well be produce with you foot pulled most of the way back - somethng that is bound to get in the way of using the finished pedal expressively.

I hope that was comprehensible and not too painful.

[rogerinIowa]

Thanks for the clarity, Mark!

I will order a couple of more suitable pots( 500k and 1Meg) and give them a try in this volume pedal. I like the idea of the compensation cap, I have used them in Fender guitars over the years but never concidered using them in a pedal, however it totally makes sense. Do you believe that it would be useful to include an output buffer in a volume pedal? Phillip has a layout for a simple output buffer on the Fuzzcentral site, designed to be used in a wah wah...my only reservation with using a buffer is that I will then have to add power to the volume pedal.

I was hoping for a good passive unit.

Anyway, I really appreciate your help on this. A topic like "building a volume pedal" is probably not juicy enough for most DIY builders on this forum, so I really appreciate your taking time to lend some guidance.