Vactrol LFO / Vibrato on Casio SK 5

[wax+wire]

Hi guys

while popping open my casio sk5 to add the Phat Philter Bank (it works so sweet!) I thought i'd add a vibrato/LFO.

I made a different circuit (http://www.555-timer-circuits.com/up-down-fading-led.html) as it is a smooth fade up down and I don't want a pulsing LED.

So i hooked it up in series with the tuning pot by cutting the trace and then put a 1K pot in parallel with the LDR because then i can control the depth.

Does this sound like a good idea?

The tuning on a SK 5 is weird.  not a linear - turn the resistor CW to make the pitch up and CCW to make the pitch lower - - it is a circular tuning system.

[wax+wire]

So i got the Vactrol working.

My tip: use this circuit but a few mods

1. Run an LED off of Pin 3 if you want a LED to show you the rate (but not fading up down)

2. for the speed/rate Potentiometer change the 33K resistor into a 500 ohm resistor in series with a 25K or so Pot.

still causes the problem that when the vibrato is engaged the base pitch isn't in tune...

this possibly has to do with the fact the LDR doesn't reach 0 ohms but 100 ohms? at the bottom of its cycle?

I can't work out whether it is better to put the Vactrol/Depth Potentiometer in series or parallel with the tuning pot either

[wax+wire]

Solved (well a work around)

Put the VACTROL LFO/Vibrato on my LTC crystal rather than on the casio's crystal.  now the pitch modulation works (though the vibrato goes down not up, but you know, that is better than nothing