Minimum Volume Circuit

[zpyder]

Hey guys...

I just wrote a bunch of shite that wasn't really necessary, so I'll just get to the point and you can read the background story below if you're interested.

I'm wondering if...

Given a passive volume pedal that does nothing more than dump a certain amount of signal to ground based on where the pedal is, how can I create a "Minimum Volume Knob" for it?  The pedal uses a system of LED's and photoresistors to determine the signal's resistance to ground.  Could I place a potentiometer and a diode or something between the dump path and output so that when the pot is all the way to one side it allows the what-would-be-dumped signal to loop back to output?  I have a hand-drawn schematic I can post.  Any pointers would be highly appreciated!  If you want to know more about the pedals I'm working with, read below.

thanks!     



I have one of those Morley passive volume pedals (first pedal I ever owned, and the only one that I *NEED* to play in my style).  I tore it open and drew out a schematic of it.  It's passive, so at full pedal volume, this thing is essentially not there - the signal just passes through -, and as you lower the pedal, it simply dumps more and more of the signal to ground.  The catch is, and also the reason why this pedal is so useful, imo, is that it has a Minimum Volume Knob so that you can set the volume level at "pedal minimum" to be anywhere between everything dumps to ground to nothing dumps to ground.  VERY handy.  The Morley accomplishes this using LED's and photoresistors.  I have the hand-drawn schematic at home and I will post it later on if anyone would like.  Basically the pedal itself mechanically blocks and unblocks the LEDs' light going to the photresistors (they're praised for the smooth action achieved by this method).  Simultaneously, the Minimum Volume Knob controls how much voltage, and therefore light, is at one of the two LED's.  Both LED/photoresistor sets must be at the proper setting to allow a full dump to ground.

I recently purchased another Morley volume pedal, but this one has some built-in other fx (wah & dist).  I mistakenly thought it had a minimum volume knob and would function like my other plus some extra sounds, but in fact, it has just a straight output volume knob.  I tore this thing open also and it uses a similar, but not same, LED design.  I haven't yet made a schematic of this thing and it's much more complicated.  For this thing to even be useful in my rig I need to mod in a minimum volume circuit.  I'd much rather do that than go sell it on eBay!

[Seljer]

connect a pot as a variable resistor between the photoresistor that goes to ground and ground?

edit: I see the Morley pedals then I see they use the pot to set a mimimum brightness for one of the LEDs, which is probably a better idea

http://www.morleypedals.com/pvoes.pdf
they've schematics for most their things on their site

[zpyder]

wow sweet, I love how morley posts their schematics.... I hadn't realized that, now I feel stupid for tracing the circuit on my volume ped!  heh...

anyways,  I kindof like your idea of using a pot as a var. resistor between the ground-dumping photoresistor and ground...........

Using the pot to control the brightness of an LED is certainly the preferred method, and is how they do it on the passive volume, but on the PDW (http://www.morleypedals.com/pdwes.pdf) the LED's are used differently.  On the PDW some of the LED's are used to control the Wah, while some are used to control volume, and the whole circuit seems to work differently than the "Just" Volume pedal.  It seems that placing a pot between photoresistor 2 and ground would just be logistically a thousand times easier....