Adding manual sweep to duo phase (biphase clone)

[idy]

I built a pedal pcb duo phase, which is mutton biphase pretty much. Not as complete calibration as the Dead End FX I see...

It works, and I want to add the option to disengage the LFO on one side and sweep manually. I put in a pot with a pull switch.. I had 250k. When I pull the switch I am cutting out the connection between SW2 pin 2 and the depth pot and etc (The LED driver.) Instead I am hooking up a voltage divider (the pot) to give an adjustable voltage to the driver, manual sweep, fixed phase.
Problem is, I can get the LED to turn off at the full CCW, but it seems to get pretty full bight in the first quarter turn.

I tried various combinations of ground and -9 and +9 on pins 1 and three (ground to 1, +9 to 3, -9 to pin 1, +9 to pin3, various resistors over 100k (270k, 500k) at each end from power to the pot, to move the voltage divider around. But the best I can get seems to be the same, quarter turn full on.

I haven't found the useful sweep yet. What would be a better way to approach this? What am I missing?

[garcho]

Could something as simple as taper help? Bright in a quarter turn sounds like classic fender tube amp volume control.

[Matthew Sanford]

I am noobish, but have questions...

What is the other block's voltage going through SW2? Maybe putting less through your pot would help put the full range back in to the LED, so a voltage divider before the pot? Also, it's a Lin not log pot?

[idy]

Taper might help.
My multimeter says the voltage I am subbing for, LFO, reads -5 to +4.

So I need to provide something in that range.
My first plan was to use two resistors to bring the lower limit of the pot to -5 and the max to +4. With the 250 k, I chose values close to 111k and 138k, 4/9 and 5/9 of 250. So 110k and 139k , using two Rs to make each side.

110k between -9v and pot terminal 1
138k between +9v and pot terminal 3.

No change in LED at all.
I short out the 110k and now I'm pretty good, the LED turns off in the first tenth of a turn...but then stays the same throughout the travel. At the lowest point I am feeding -9v to the driver.

I measure about 0v when the pot is maxed. I measure 9v at the charge pump pin 1 and 8, 2.69v at the junction of the 100k and 39k, and 0 volts at the pot pin 3.
Is this a loading issue or something? Wrong value for pot or something?

I will try a different taper too. A or C.

[Matthew Sanford]

Perhaps running it through a 560r to the depth pot to match it's ground side could reduce the current? Possibly with pin 1 on new pot to ground instead of -9v? Just throwing it out there, I'm noob so hopefully a smarter person will weigh in

[idy]

Thanks for mentioning the depth pot. I think the trick is just to use that as the manual sweep: Instead of a pot with a push pull just add a toggle that cuts the LFO and gives a voltage from +9 with a resistor. The Depth pot gives a useful sweep this way.

[Matthew Sanford]

Glad it's working. I'm working on wiring my pots through stereo jacks so I can cut them out by putting a cable to an expression pedal of LFO...takes up a lot of space, but sounds like it'd be useful here