Vox Wah LED/LDR remote mod unexpected BONUS

[aab0mb]

Been awhile since i've hung out around here.  Greetings all.

I had a vox 487 ( i think that's the one without the power jack) sitting around for awhile that i wasn't using on the current board.  However, missing that classic wah sound i dug it out with the intention of fixing it up to my liking.

As i'd done before i implemented all the usual mods such as the gain/bass pot, mid resistor boost, Q pot, resonance lowered with a small switch...  But alas the classic scratchy pot got me in the end.

Having read the tech of wah article about a million times the burning desire to see if the remote/scratchy pot fix worked well. I rolled my own radio shack led ldr optocoupler and got the circuit working with the omission of the 100k resistor that was supposed to make up the top half of our pseudo pot arrangement.  So i guess i was left with a resistor to ground setup. 

The sound is delightfully smooth and static free.  The sweep seems pretty dang good as far as i'm concerned.  But the thing that was the MOST interesting was the interacting between the newly added controls and the LED/LDR.  Where the gain knob max with a traditional pot would result in self oscillation at the heel position of the pedal, the opto mod will have NON of that. Instead it results in Very deep and resonant bbbwwwaaaahs with a ton of bassy goodness. The normal ranges are all still in there as well.  For whatever reason the LED mod made that gain knob into a really sensitive and useful control combined with all the other mods.  Hooray for unexpected tonal control.

I highly encourage anyone else to mock up this little test and see what it does.  Pleasing results.

Chime in if you've experienced the wah remote mod at all.  I'm pretty enamored with the while optocoupler idea for other fx.   

One thing that i didn't get was in the tech of wah article there is mention of playing with the resistance to ground control in a number of ways.  Traditional pot, led/ldr, etc.  The two i'm wondering about are the diode string (new concept for me) and the envelope detector to VC i guess it would be...  Envelope follower mod to a regular wah pedal on a switch is what i'm thinking.  I understand a little about the difficulty of guitar envelope filters and "ripple" is it? I wasn't getting it all in my reading on the subject.

cheers.

[candidate]

you measured the ldr light/dark resistance?

[aab0mb]

I measured it while i was testing the circuit to make sure it was working but i don't know what values it's functioning at within the completed mod.  It just seems to work.

The interaction with the higher gain and bass mod is what was the really interesting thing to me.  Very synth like and no self oscillation like with a pot.

[alfafalfa]

you measured the ldr light/dark resistance?

I know you don't know the values but that really is a pity because that's what counts.

I would really like to try your find but that's only possible with the right info especially about the LDR.
I have a few scratchy wahs lying about. On one I gave up after receiving a brandnew scratchy pot from New Sensor right out of the box, and the pot didn't come cheap.  As I live in Europe  it was too much of a hassle to send it back.
So using the ldr would be the solution. 
I once tried a bourns conductive plastic pot 100K linear but the taper was all wrong, so it didn't give the right results.

So could you please check the values , I thinks it would be of great benefit for a lot of people.

Alf

[aab0mb]

I think the easiest thing to do is mock up the circuit changes point to point and use some alligator clips while dialing it in.  It did take a fair amount of fiddling. At one point I had a pot in place of the current limiting resistor and the 100k reisitor above the LDR. I think it's hard to measure an LDR specifically because it goes from like 0ohms to above a few megs.  I can't even go that high on my meter.  THe point is ( i think )  HOW it gets from zero to full power with the pedal sweep.  At first while just turning the pot by hand i thought that it wouldn't sound correct. But once i took out the 100k resistor and actually put it in the pedal so i could feel the action it seems to work just fine.  I got a pack of LDRs from radio shack but in the end the parts that i used were an LDR from a night light i broke apart before i found the LDRs at radio shack (LOL) and a 5mm green diffused LED. The LED isn't even really all that bright. 

Glad to help out any way possible and if you have ideas about how to measure the LDR let me know.