Minimum Gain on Expandora (Pandora's Box)

[nate433]

Hey ya'll i have a quick question about gain wiring and adjusting the minimum gain. I'm loving the expandora, but i don't like how when the gain is at 0 the effect volume goes to 0. So instead i want to essentially limit the gain knob so that fully CCW is equivalent to like 5% rotation of the original (value depending on testing. I assume 50k-ish since it's 5% of 1M). It seems like it's a quirk of the pedal since it does it on the circuit board (Aion FX version) and when I breadboarded it.

I'm happy where the gain is at max, so ideally don't want to lower the max gain. So would that mean i would need to put say: a 50k res on lug 1, lower the Gain pot to like 500k, then add another resistance of 450k on pin 3. If it's whatever method is easier/better ups the gain a bit, then no harm no foul

I've seen how to limit the gain by adjusting/adding a resistor to ground, but never in a feedback loop like this one. So 2 questions:

1. Would you change the gain pot value and compensate with a series resistor? OR
2. Would you just tack on a resistor to one end of the pot (and if so which side? A or B)

A B



Thanks!

 

[BuddytheReow]

Looking at the PPCB schematic, do the second option. I would personally use A. The configuration is an inverting feedback loop. So, to get unity volume in that stage tack on a 100k resistor. Max gain will be increased by 10% and may start oscillation. If you want some volume when pot is at zero, try 10k (just off the top of my head).

 

[Chuck D. Bones]

Find the lowest GAIN setting you're likely to use, measure or estimate the GAIN pot resistance and add a series resistor of that value. I prefer config A, but either will work. No need to worry about the very slight increase in gain at the top end of rotation caused by the series resistor. No danger of oscillation.

Which switch settings do you use? If you don't use Forbidden Mode, but would like a higher gain option, then try a 10K resistor in parallel with C7.