Converting CryBaby Wah into volume pedal

[Henry89789]

I have an old crybaby I want to convert into a volume pedal. I have done some research on this and it seems rather simple but have read that using the original pot on the cry baby only allows the pedal to go from quiet to loud and not from silent to loud. I would want the pedal to go from silent to loud.  I found these two statements:

1.   the potentiometer (your volume pot) had a resistance range that couldn't completely cut your signal. The only way to fix this is to a get a different volume pot... something with a steeper curve (more sensative) or a logarithmic curve (more sensative around 0-1/2 volume, less sensative near max volume. Also make sure your pot has the correct resistance for your application.

2. A pot has three pins. If you put one pin to ground, the other to in, and the MIDDLE one to out, it will go from silent to loud. I don't know what a good impedance would be in this case though. If it's to low, it will lower your total signal. If it's too high, the pedal will go 'silent,silent,silent,silent,silent,LOUD'.  I don't know what a good impedance would be in this case though.  You'll probably have to experiment. I'd start with getting a 1k and a 10k pot and try those.

Questions:

a. Are both these statements correct ?   

b.   What is the optimum  resistance for a pot to be able to go from silent to loud? 

c. The original cry baby pot is great because it has a gear that meshes perfectly with the toothed "shaft" attached to the moving part of the pedal.  Alas, it is not optimum. I haven't tried to remove the gear  because I don't want to mess it up by doing it wrong. It seems to have no set screw. It also seems like it will just slide of the pot's shaft.  How do you remove the gear from the pot shaft?

d. Can an optimum pot be found  on which the gear from original crybaby pot will fit (the original pot has a shaft with a flat side to key the gear) ?

e. How is the pot wired to the sockets?   I read that adding  a cap and/or  resistor helps improve the sound when rolling off the volume. How is the cap and/or resistor wired in?

f. Any other considerations to take into account when doing this project?

I apologize for the long post but I wanted to be sure that I included enough detail. Thanks in advance for your help with this.

[joegagan]

the crybaby uses about a 3rd of the pot's rotation. almost all commercial wahs use a taper that concentrates the majority of the sweep of the resistance over the specific range.

you have a fork in the road here: passive or active.

passive:for a passive volume pedal to go to zero, your max resistance at toe down on pedal is usually less than full value , even with a log pot. ( usually a 100k will get to around 50 -70k when heel down is set to zero. this is usually a bad range for passive guitar. . so, to stay passive, you can do what commercial volume pedals do going to a 250k, 500k or 1 meg pot.

250k will still give a limited range, but  might sound ok with your setup.

500k works, probably a little more linear in feel than a 250k if used in a crybaby shell.

i have built vol pedals for customers in crybaby shells using RV4 style ( large military style) allen bradley 1 meg linear pots. the range on those in a cryabay usually hits about 450-500k max at toe down when adjusted to zero on the opposite position. the sweep is reasonably linear in feel and sound with passive pickups.

ernie ball sells their vol peds in active and passive models. the actice are 25 k, passive 250k. but these work very differently than a pot in a crybaby shell - - their string mechanism allows the full range of the pot to be used. so a 250k pot goes to full 250k when toe down , etc.

active:

you can get by with a max value of 25 k or the aforementioned 100k wah pot maxing out at around 50k if you have a buffer ahead of the vol pedal, or if you build a buffer or booster into the vol pedal.  how it reacts depends a lot on your pickups, guitar electronics, other pedals in line, etc.

do you use a tuner at the front of the chain? where do you intend to place the vol ped in the chain? what type of guitar is it?

i can tell you more about swapping gears around, but it is possible that we could make a standard crybaby pot work for you, first things first.

[Henry89789]

Joe:

Thanks for the reply.   Let me give you  "the first things first"  facts:

1. I have several guitars. A couple have Seymour Duncan Pearly Gates, JB and Jazz humbucker pickups w/ three way switch, and one volume and tone pot.  But the ones I want to sound best (if it makes a difference in regard to the volume pedal project) are the Strats (one US Standard and one MIM) and the US  Standard Telecaster. 

2. Yes there are quite a few pedals including distortion, overdrive, compressor, wah, reverb, modulation, and delay. There is a TC Polytune  at the beginning of the chain. And in regard to where the volume pedal would go, I am flexible and can place it where it will work and sound best. I have read that it should go b/w the last pedal and the amp (Vox Night Train) but as I said that is flexible if another placement is better. 

3. In regard to active or passive. I am leaning toward passive because it seems like a simpler project ( I am a beginner at this and the idea of building in a buffer or booster is a little intimidating) but if making it active is not too complicated or too expensive for the parts (and would make it a more interesting project) then I can go with active. 

It would also be great if we could make the standard cry baby pot work.   Thanks again for taking the time to think about this and respond.

[joegagan]

ok, with all those pedals, there are undoubtedly numerous buffers inline and 'on' even when the effect is off, so try this simple experiment. if your wah has an existing pot and  it isn't scratchy, just wire it up like any passive volume pedal. ( google morley volume pedal schematic). then adjust the rack gear by loosening the nylon retainer on the straight gear. find the setting where the pot is almost bottoming out on the low end, listen , you should hear it passing no signal at this setting. lock it down and try it with your rig at the end of the chain like you mentioned. it has a good chance of working fine. if the sweep isn't good, get back to me and we have some more easy things to try.

be careful with your adjustment, you want to limit the pedal's travel with that heelside rubber bumper so that it takes up the shock at end of the travel, not the pot. it is bad for the pot to be run all the way to the end - you might be running it very close to the end to get zero volume at heel down..

[ashcat_lt]

The long shafted pots from a Les Paul will fit in place of the Crybaby pot.  The gear will fit and the knurls will kind of "bite" into it to hold it secure.  Two problems though.

1) The pedal turns the pot in the wrong direction. If you want a logarithmic action with louder at toe down you need an anti-log pot.  I used a linear pot with tapering resistors, but mine is active.

2) It won't turn the pot all the way.  You can adjust the gear to get all the way down to silent, but then you won't get all the way loud.  You'll also risk damaging the pot - the reason they make em this way.  I opened up the pot and carefully painted along the track with conductive silver paint to shorten the active region.  This reduced the total R of the pot - another reason mine is active.  When I say active I mean there's an opamp buffer on either side of the pot.

[Henry89789]

I found a schematic for the Morley CVO which was the simplest schematic for a Morley volume pedal.  I  looked for schematic symbols  for the jacks in the Morley schematic but none were the same.  I attached the ones I found. Which of the jacks in the picture  is the one represented in the Morley schematic? 

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[Henry89789]

Let me try the pics again ....







None of the schematics in the second pic are exactly like the one in the first pic.  My guess is that  the jack on the right  in the colored pic is the one in the morley schematic.

[joegagan]

you don't have to get all fancy with the jacks. normal mono 1/4" jacks will work. just wire it like this.

[Henry89789]

Joe:

I wired up the jacks to the crybaby pot per your diagram and it worked pretty good with my small practice amp. I set the gear so that it went from low volume to loud on the small practice amp. But when I tried it on the Vox Night Train the change in volume was barely noticeable as if you needed a much longer travel to change the volume. What can you suggest now?

[joegagan]

what is the signal chain in this test?

[Paul Marossy]

You could try removing all the rubber bumpers from front and rear of the wah shell to help increase the amount of rotation you can get out of the pot. But it won't get you that much more.

[Henry89789]

With the Night Train, I tried both ways;  guitar ---  volume pedal  ----  amp;   guitar --- pedal chain --- volume pedal ---- amp.  No difference.

[joegagan]

just  for fun,, try a buffered pedal in the off position after the volume pedal before the night train.

you could try limiting the overall R of the 100k pot with tapering resistors ( see geofex 'secret life of pots), see if lowering the resistance helps the situation.

[Henry89789]

I added a 100 pf cap between  the two tip connections on the pot. I had also wired it backwards so that the volume was reduced with toe down instead of heel down. So I fixed that. I don't know which of these things  (or if both ) made a difference but now it works  with the volume pedal between the pedal chain and the amp.  The only problem now is that the volume goes from silent to loud to very loud. Is there a way to get a smooth, gradual increase in volume from silent to very loud?  Will the tapering resistors help with this?  Thanks for all your help with this.

[Paul Marossy]

The only problem now is that the volume goes from silent to loud to very loud. Is there a way to get a smooth, gradual increase in volume from silent to very loud?  Will the tapering resistors help with this?

That's the pot taper, you're kind of stuck with that. Tapering resistors might help. Or getting a different pot to put in there (one that is not designed specifically for a wah pedal).

[Henry89789]

Thanks for the replies everybody. I am going to try the tapering resistor. A different pot brings up problems involving the pinion gear which I want to avoid. I read the article on Geofex re: Secret Life of Pots and quite frankly it was full of so much technical jargon and written in theoretical terms that I did not find it of practical use. After reading it I do now at least  understand how pots work internally and the concept of "taper".  I would have to read it a couple more times to get more from it.

I am good at following instructions and if it would not excessively try you all's patience, please give me some detailed instructions on how to install a tapering resistor. Please tell me how many ohms the resistor should be and where to connect each leg of it. My guess is one leg to the tip lead of the input jack  and the other leg to the pot terminal where the tip lead of the input jack would ordinarily go. But as these things go, it is probably not that simple. Thanks again.