Expression Pedal questions Neovibe

Started by rhdwave, October 15, 2007, 11:06:54 AM

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rhdwave

Hey all, i've been researching adding an expression pedal to the neovibe (which i have not actually built yet, but i like to do all my research before beginning a project if possible).  I've read the three excellent articles by R.G. on adding an expression pedal, the LERA article and the fix for dual ganged pots all on GEO. 

I was a little confused by a couple of things however.  I was just looking for some confirmation that i understand correctly what he was saying.  First: In order to add a pedal to control the speed on the Neovibe, one would need to get an identical pot as the speed pot obviously and install that in the rocker of the pedal.  In the case of the Neovibe this is that dual-ganged reverse audio taper pot, so one would need the same kind which fits in the rocker of the expression pedal.  I know this sounds pretty straight forward, but i just wanted to make sure i understood this correctly...

Second, is the reason one might want to make the modifications using the dual ldr/led module that R.G. describes in place of the dual ganged reverse audio pot that these are difficult to obtain, at least those that might fit in an expression pedal assembly? And if you used this alternative layout, you would only need a 10k pot to hookup in the expression pedal. 

Lastly, are there any other advantages to the alternative dual ldr/led module, for it seems beyond the expression pedal parts, small bear i think sells the dual reverse audio pot (at least for the generic speed control in the pedal itself not the expression pedal rocker part). 

Hope what i'm asking is clear and i'm grateful for any responses!!!

Much thanks!

RedHouse

#1
Quote from: rhdwave on October 15, 2007, 11:06:54 AM
Hey all .... this is that dual-ganged reverse audio taper pot

Well I cannot (and would not) presume to speak for RG and his wonderful Neovibe, but until he chimes-in on this thread I do have a couple things to pass on regarding using vibe's in expression (wah-shell) pedals and the pot's for that.

The hard-to-get dual-reverse-log pot is only needed in a regular knob-turning style stompbox, the wah-shell rack-n-pinion reverses the action so you would use a regular Dual-Log pot (see RG's Neovibe PDF).

My experience is that finding a pot that will physically and functionally fit is a real challenge, like say if you try to use a standard 24mm Alpha dual-pot like this:



you will immediately run into these three issues:


  • the Alpha pot's body is too long, won't fit into the square hole in the wah-shell, second gang in the unit hits the wah-shell
  • the Alpha pot's shaft bushing is too short, won't allow a washer on both sides and still have enought thread left to screw on the nut with the built-in pot bracket
  • the Alphs pot's shaft is a wee bit too short, barely allows enough shaft for the pinion gear to slide on (and stay)

Using the 16mm Alphas fixes the first problem but makes the second two even worse... bummer!

On my first pedal what I did was modify the wah-shell by removing the stock cast-in pot bracket and added a .090 aluminum right-angle bracket in it's place and then the Alpha pot  worked because I could move it over 1/8" correcting problem #1 above, and the .090 aluminum bracket accepted the short bushing correcting problem #2.

CTS has nothing better to offer that I can get hold of, and searching Mouser, Allies, DigiKey, Jameco, Parts Express and surplus catalogs didn't come up with any better alternatives  ....until



As luck would have it (or lots of perservirance) while on holiday over in the UK (my wife is Scottish and we visit her family there) I found these which fit the bill exactly, they are sold by a company named "Maplin" under part number FX12N:



http://www.maplin.co.uk/Module.aspx?ModuleNo=2207&&source=14&doy=Search

These have a long enough bushing which is of an appropriate size to fit the built-in wah-shell pot bracket, they have a small profile 16mm body and fit the hole in the wah-shell, finally they have a long shaft that can be trimmed to the exact length.
(in fact if you leave it long it can stick out through the side of the wah, add a knob, giving a "manual" speed adjustment knob)

This one's a slam-dunk, you cut the shaft to length, file a flat on one side of the shaft, put a drop of super glue on the shaft, slip the pinion gear on, then mount the pot in the wah-shell just like the wah's original 100k pot was mounted and schwiinnnggg!

Maybe next time one of our UK brothers or sisters want's some stuff from Mouser or a US company, one might ask them if they'd do a snail-mail swap for a couple of these.

I hope you find this info helpful, and I'm sure RG will be along soon with some great alternatives for you.

{EDIT}  PS, for me the whole thing isn't an issue any more, as most folks that have used mine have agreed the speed pedal isn't that great a thing, most find it annoying if they set it for a song and accidentally bump it because the speed is often set with some relationship to the tempo of the song.

Also there is another annoyance when the pedal effects the speed, even if you use true-bypass you still have to disturb the speed with the pedal to switch the pedal on/off as the switch is at the top of the pedal's throw so you can't switch the effect on or off without messing up the speed setting which in my mind was one of the original univibe's problems with it's foot controller.

The last one I built had the wah-shell pedal controlling the "intensity" rather than the speed which seemed more useful and repeatable on stage.


rhdwave

Redhouse,

Thanks for the extremely informative reply.  I've been doing a lot of research on this topic and this has really put things very clearly.  Just a quick question re: the intensity expression pedal vs. the speed...in terms of the neovibe, i'm assuming this would refer to the depth pot? Also, i understand that the speed control can be at times annoying in the expression pedal as you have said in reference to accidentally hitting it etc. but i wasn't quite sure what you meant by turning it on and off, unless it was a reference to putting the whole project inside of a wah shell.  I was thinking it might be better to build the neovibe in its own enclosure and then have an extra output jack just for the expression pedal, thus the on/off of the effect would be controlled not by the switch on say a wah pedal where you must lean all the way forward to turn it on and off, but by the stomp switch on the original box itself. 

Would this solve that issue or am i reading this wrong?

Also, since i have nothing to go on since i haven't built this yet, though half of my parts have arrived today, how does the effect sound when you use the expression pedal as a rocker similar to a wah where it's in a more constant up and down motion as opposed to just dialing in a speed and then leaving it there?

Again, Much thanks for the reply, it has cleared a lot of things up for me!

RedHouse

Quote from: rhdwave on October 16, 2007, 01:14:25 AM
Redhouse,

Thanks for the extremely informative reply.  I've been doing a lot of research on this topic and this has really put things very clearly.  Just a quick question re: the intensity expression pedal vs. the speed...in terms of the neovibe, i'm assuming this would refer to the depth pot? Also, i understand that the speed control can be at times annoying in the expression pedal as you have said in reference to accidentally hitting it etc. but i wasn't quite sure what you meant by turning it on and off, unless it was a reference to putting the whole project inside of a wah shell.  I was thinking it might be better to build the neovibe in its own enclosure and then have an extra output jack just for the expression pedal, thus the on/off of the effect would be controlled not by the switch on say a wah pedal where you must lean all the way forward to turn it on and off, but by the stomp switch on the original box itself. 

Would this solve that issue or am i reading this wrong?

Also, since i have nothing to go on since i haven't built this yet, though half of my parts have arrived today, how does the effect sound when you use the expression pedal as a rocker similar to a wah where it's in a more constant up and down motion as opposed to just dialing in a speed and then leaving it there?

Again, Much thanks for the reply, it has cleared a lot of things up for me!

Oh yeah, I'm sorry I forgot that RG calls the Intensity control "Depth" on his Neovibe.

QuoteI was thinking it might be better to build the neovibe in its own enclosure and then have an extra output jack just for the expression pedal, thus the on/off of the effect would be controlled not by the switch on say a wah pedal where you must lean all the way forward to turn it on and off, but by the stomp switch on the original box itself. 

You would definately be fine with a two-piece arrangement like the Dunlop Uni-Vibe:



where you have a stompbox with the PCB in it, and in/out Chorus/Vibrato switches, then a separate pedal used as the speed (or depth/intensity) controller.

I was yacking too much in my post about the troubles with using the wah-shell as a single housing for the univibe effect and kind of side-tracked your point sorry.

If you wanted to use the pedal like a wah, where the pedal causes the basic effect as an expression (in this case, to phase shift) you might look into the way a Boss BF-2 Flanger works, it has a "manual" pot that changes the bias of the LFO output, this idea could be used in a univibe to cause a manul phase shift sweep with the pedal. I've dinked with it a little but lost interest (more like lost the spare time to dink around with it) and dropped the ball. JC Maillet's "bias offset mod" might just be the ticket for that kind of thing, try going here and look down the page at the section "About the Bulb and Bulb Driver circuit": http://www.lynx.bc.ca/~jc/pedalsUnivibe.html



If you moved the cancel switch over to the high-side of the intensity/depth pot (where the negative end of the Electrolytic cap is shown in the following pic) then the 100k pot shown should get you manual pedal operated vibe'ing.








rhdwave

Thanks again Redhouse!

Here's another idea.  I looked up those dual-gang 100k log pots 16mm and was all set to buy.  However, now i see why you included that bit about hopefully knowing someone in the UK, as they wanted to charge something like $60+ for shipping.  I had gotten all the way to checkout and then saw the total price as some ridiculous amount and promptly withdrew the order.  So, i was thinking of using the standard dual-gang 100k reverse log pot for the pedal and then what about building a daughter board with the RG Keen modified univibe LFO and putting that inside the expression pedal? This way, i wouldn't have to mess with the pcb layout and i could use a normal 10k pot in the rocker assembly.  Any thoughts on this?


RedHouse

Quote from: rhdwave on October 17, 2007, 07:54:07 PM
....and then what about building a daughter board with the RG Keen modified univibe LFO and putting that inside the expression pedal? ....

RG's your man for that rhdwave, I'll need to step aside here and give him the opportunity to guide you with his ideas.

rhdwave

Thanks again Redhouse! Hopefully RG will respond.  If not, thanks for all the insight.