Hall-Effect Volume/CV Pedals

[WeAreAs1 at aol.com]

WeAreAs1 at aol.com wrote:

<< Roland made a few pedals that used Hall Effect sensors, back in the late 
70's/early 80's.  They were the "Rocker" pedals. >>

to which Harry Bissell responded: 

<< I'll bet if they were making a wah out of it, it
probably wasn't a hall effect device. Old Maestro and Cry-baby wahs used a
fixed inductor and a tuned circuit using a pot. See my other post of "slug
tuned" inductors. I'll bet they made a variable inductor. >>

OK, Harry - I'll take that bet!

I looked trough my old effect schematics and I found the Rocker pedal stuff.  
There are three of them:  Rocker Volume, Rocker Wah, and Rocker Distortion.  
Each one uses Hall Effect devices to control their circuitry.  The wah still 
has traditional wah filter circuitry, with the old 560uH choke, but the Hall 
Effect sensor is used in place of a pot.  The pedal moves a magnet past the 
sensor somehow.  Unfortunately, there isn't a mechanical drawing of the pedal 
actuator, so I don't know how the magnet moves, how close it is to the 
sensor, or how far it moves.  They do have a log amp after the Hall sensor, 
problably to help linearize its response (or compress its range). 

Ironically, the Rocker Wah uses the Hall sensor to control the brightness of 
a couple of LED's, which shine onto a couple of photoresistors, which are 
used to sweep the frequency of the wah.  What a schizophrenic mess!

I'll try to get these scanned and mail them to those who are interested.  It 
may take a while, since I don't have my own scanner, so please be patient.   
It's doubtful that this particular Hall device is still available, but there 
may be some kind of contemporary substitute.

Michael Bacich