Maestro PS-1a Mod Help

[maxwellravitz]

Hello,

I'm admittedly a noob when it comes to circuit diagrams. I've done a lot of DIY modular synth building, but mainly with instructions involved, and I want to do a modification that doesn't seem to be that well documented. I have a maestro PS-1a phaser, and later in the manufacturing run there was a maestro PS-1b that has a variable speed control for the phaser LFO. I would like to add the speed control, and was looking for help identifying where in the circuit the speed pot needs to be placed. Also given that there is a trimmer for oscillator depth, I'm thinking of adding a variable panel control for this. I've included a schematic diagram, can anyone assist me pretty please?

[eatyourguitar]

why don't you just look at the other schematic? failing that, pot (or trimmer?) in the bottom left will bias the transistor that sets the speed of the LFO. there is a 3.9K pullup from the red switch connected to a pot connected to a 100k pull-down (-12v). the 1M can be deleted.

[multi_s]

why don't you just look at the other schematic? failing that, pot (or trimmer?) in the bottom left will bias the transistor that sets the speed of the LFO. there is a 3.9K pullup from the red switch connected to a pot connected to a 100k pull-down (-12v). the 1M can be deleted.

the schematic provided seems to be for the 1a AND 1b (Versions 2 and 3 according to pic) or maybe op updated since you posted....

the variable pot in the 1b is likely the 2meg pot labelled "R4 2MEG PS1B ONLY"

im just going to go out on a limb and say that is probably your guy.

[eatyourguitar]

I can't read shit that small. I guess its the black box you read that?

[multi_s]

ya it's definitely not that clear, but to be fair the text in the box is the same size as the resistor values, "red" etc you seemed to do fine with (:

[maxwellravitz]

ah shit, right you are. Somehow missed that little box. so it's just a 2m audio pot...