Anyone know about Light Dependent Resistors (LDRs) on wahs?

[xpaladin1313]

I was thinking of building the mod-able wah from General Guitar Gadgets, so I bought an old broken wah pedal (Morley PWA Pro Series).  The thing is, I opened it up and found that instead of using a regular pot, Morley uses the LED/LDR combo.  Now, I'm not sure what's wrong with the pedal, but I really don't know much about LDRs either.

If I'm correct, an LDR has very high resistance with no light, and a lower resistance with light.  Is there any way I could modify the GGG wah to use an LDR?  Would it be better to glue a little gear part onto the expression pedal to turn a pot?

Any help would be appreciated.

http://www.generalguitargadgets.com/index.php?option=content&task=view&id=149&Itemid=177

[varialbender]

Even if it's working with an LED/LDR pair, it still needs a pot in the wah to control the brightness of the LED. Voltage is passed through the pot in the wah, and into another current limiting resistor maybe? then into the LED, then into ground. The LDR sees that brightness, and uses that as the resistance.
Warning: the previous post was made by a noob and should not be taken as valid information.

[xpaladin1313]

Well, the way the Morley expression pedals are made (to my limited understanding, that is) is that the LED and LDR are on opposite sides of a plate connected to the pedal.  The plate has a hole in it that changes how much light the LDR can see.  So really there's no pot at all.

I'm just not sure how I can use that....

[varialbender]

Oh, I see, weird... Glad you shared that with me, I've never heard of that.
But yes, an LDR is still a form of resistance, so with the right values it should work.
See how much resistance and how little resistance you need to run the circuit you want to build, and compare it to the amount of resistance your LDR is giving. It might be a bit different, but within a certain range, it might be acceptable.
Sorry, can't be of much more help, maybe someone else can chime in.

[xpaladin1313]

Hmm... I suppose that means I'll have to use my multimeter in the dark, eh?  How sensitive do you think the LDRs are?

I wonder how you design a circuit based on the amount light it's going to receive... weird indeed.

[humboy]

hi, have you had a look at http://www.geofex.com/Article_Folders/wahpedl/wahped.htm  ? that should answer most of your
questions. You could also look at http://www.morleypedals.com/downloads.html to find out how the LDR is applied (the schem of the PWA can be found somewhere in the middle of the page.)

[Paul Perry (Frostwave)]

At one stage, a number of 'crap' led/ldr shutter type wahs were turning up in my local secondhand music store. They must have missed out on quality control, because what they needed was just bending the LDR leads to tweak the response. One was hacked up where some poor bastard had tried to replace the LDR. Tragically, the only one I could find that worked right (without modifying anyhing) was a LDR I cut out of one end of a CLM600.