replacing a 250k pot with an expression pedal input

[ScrewitIllDoitMyself]

I wanted to be able control the amount of reverb on an external spring tank.
I need to use my feet. knob wont cut it. Is this a basic swap, or am I going to have to get crazy on this.

any help would be most appreciated. THANKS!

-D

[Mark Hammer]

You'll need to specify a little more.

Is your goal to foot-control:

1) the "push" applied to the tank?

2) the blend of dry and wet?

3) the reverb on an amp or an outboard reverb effect?

Do you have a separate mixer or does the reverb have its own blending circuit?

And why 250K?

Not saying it can't or shouldn't be done.  Just need to understand a little more about what needs to be accomplished.

[ScrewitIllDoitMyself]

You'll need to specify a little more.
Is your goal to foot-control:
1) the "push" applied to the tank?
2) the blend of dry and wet?
3) the reverb on an amp or an outboard reverb effect?
Do you have a separate mixer or does the reverb have its own blending circuit?
And why 250K?
Not saying it can't or shouldn't be done.  Just need to understand a little more about what needs to be accomplished.

Hey Mark..
Sorry for being Vague.

Only thing I wanted to do was control the amount of dwell (drip) with my feet. (this is a fender reverb spring unit)

i dont have a separate mixer. The reason i said 250k because that's what the specs were on the schematic for the dwell knob.

thanks for your help buddy.  

[Mark Hammer]

OK, now I see what you want to do.

I suspect the first thing to consider is that you probably don't want to simply run a stereo conductor out to a footpedal, with a replacement 250k pot.  I mean, you could do that, but it's the sort of thing that invites noise getting into your signal path.

Perhaps a more sensible approach is to use an external foot-pedal to control a pair of photocells that duplicate the function of the 250k dwell pot.  I remember we had a thread here last fall about a Morley pedal where a "reciprocal illumination" scheme was used.  That is, two photocells with individual sources of illumination, and the more you light up one, the less you light up the other.  The nice thing about that is that the cable out to any controller pedal would not be carrying audio signal, such that noise would not be an issue.

The other qualifier here is how much control you want.  The Dwell control on a Fender reverb unit essentially serves as an attenuator for the "drive" front end, going into the reverb pan.  It does not itself adjust gain.  The gain is fixed, and the Dwell control simply reduces the amplitude of the input signal that gain is applied to.  But what that also implies is that if one reduces the Dwell a lot, then you may as well shut the unit off, or hit a bypass switch.

And do you really want to control the Dwell function, or do you really mean to foot control the Mix, and blend in varying amounts of reverb?

[ScrewitIllDoitMyself]

i wanna control the amount of SPLASH like on the fly..

from light to some serious Springy Batcave Dick Dale time.. similar to what the Dub Reggae guys do on the boards.. but just with my foot.

The noisier the springs the better!!

[Mark Hammer]

Then Dwell it is.

[ScrewitIllDoitMyself]

Then Dwell it is.

Awesome. Thanks Mark.

So what do you think would be the best option for JUST the Dwell control. Photocells or just the stereo conductor option you suggested?

[joegagan]

small bear is a good source for my specially prepped 250k wah pots. log taper. i believe they might give a good response for a verb dwell vs a lin, since the log taper comes close to a linear curve when translated to the rack and gear mechanism of a wah shell. we also designed a smaller gear that meshes with the standard rack so the full R value is attained in a standard  crybaby or vox type shell.
http://www.smallbearelec.com/servlet/Detail?no=1430

sorry for the spam, but since you are new i thought you might like to know. some dunlop volume pedals used 250k hotpotz2, which is also a very good pot, and probably a similar taper.

search geofex for ' adding an expression pedal output', great article on doing what you are doing. if i understand , i think you could run your wires from the pot out to an external pot in a wah shell using jacks.

[Mark Hammer]

What Joe describes is about as simple-and-elegant a solution as you can get.  Personally, I still have some anxieties about running audio signals out to such control footpedals (and in this case, it's not like the unit is sitting in a pedalboard with a 2ft cord), since you basically have the length of the wire out to the footpedal and back to the reverb from the footpedal.

On the other hand, it's not like there is that much bandwidth in reverb to begin with, so my misgivings may just be a dumb overreaction. And while Joe suggested using what is a wah pot, you're not intending to use it like a wah (i.e., constantly pumping it up and down), so it should enjoy a long crackle/noise-free lifespan.

[ScrewitIllDoitMyself]

Thank you both for your help!! I really appreciate it fellas.

[ScrewitIllDoitMyself]

Found all the info.. AWESOME!