Expandora Forbidden toggle with its own volume knob?

[nate433]

Hey guys. I've been working on a modded Expandora aionfx board. I moved the forbidden mode onto a footswitch with an LED indicator, but when playing live I didn't always like the huge volume jump. So i wanted to put in an alternate volume knob just for when i'm in that mode. Does all this wiring look kosher to you?





Thanks!

 

[Feral Feline]

Hey guys. I've been working on a modded Expandora aionfx board. I moved the forbidden mode onto a footswitch with an LED indicator, but when playing live I didn't always like the huge volume jump. So i wanted to put in an alternate volume knob just for when i'm in that mode. Does all this wiring look kosher to you?


View attachment 90884


Thanks!

No, sorry, not kosher.

You will have interactions between the two pots, parallel resistors have odd interactions:



So your two variable resistors are 1M each.
Full on in parallel they will be only 500k each, but since they are variable, if you have LEVEL-A set to 750k and VOL-B is set to 250k, then while using LEVEL-A it's actual output will be...
187k5

Besides considerations regarding the math involved in Parallel resistors...

Compare PedalPCB's, Aion's & Madbean's schematics, rather than most VOL-pots wired as voltage dividers all three schematics here tie LEVEL's LUG-3 + LUG-2 to form a rheostat:



Whether connecting to PIN-6 of the op-amp ala PedalPCB's version or PIN-7 of Aion and MBP's circuits, LUG-3 & LUG-2 are tied together on the PCB itself...
...so your "input" wire to the LEVEL pots, that's also connecting the two LEVEL pots' LUG-3 means you'll have 4 lugs of both LEVEL-pots all tied together (both #3s and #2s), which negates you having switching between LUG-2 of each LEVEL pot since now they're all connected on the PCB via your wiring.

An aside, I almost missed your pot-lug numbering, it's VERY faint, and at first glance I thought you had LUG-3 on one pot wired to LUG-1 of the other.


I previously made a GAIN-POT swapper diagram, I've re-jigged it for you (since the "LEVEL" is more of a GAIN-pot anyway).
You'll need to offboard-wire both pots, and that way you won't have any interactions between the pots.
Also note, there is no connection for MODE switch's LUG-3 in the schematic, so you don't need a wire for it, just leave MODE's PAD-3 and LUG-3 empty.
Mod the LEDs to however you like: one LED, one bi-colour LED, one LED that's either dim or bright ...

 

[nate433]

Wow thank you so much for such an amazing response and drawing up a diagram. I didn't even consider that it would be different depending on how the pots are wired, but like obviously it would

I just assumed it could use the same thing that i've done in the past when switching pots, By using this method that i've seen shared around. Since i've used this for for my barbershop and a couple other gain pedals.

No, sorry, not kosher.

You will have interactions between the two pots, parallel resistors have odd interactions:

View attachment 90936

So your two variable resistors are 1M each.
Full on in parallel they will be only 500k each, but since they are variable, if you have LEVEL-A set to 750k and VOL-B is set to 250k, then while using LEVEL-A it's actual output will be...
187k5

Besides considerations regarding the math involved in Parallel resistors...

Compare PedalPCB's, Aion's & Madbean's schematics, rather than most VOL-pots wired as voltage dividers all three schematics here tie LEVEL's LUG-3 + LUG-2 to form a rheostat:

View attachment 90935

Whether connecting to PIN-6 of the op-amp ala PedalPCB's version or PIN-7 of Aion and MBP's circuits, LUG-3 & LUG-2 are tied together on the PCB itself...
...so your "input" wire to the LEVEL pots, that's also connecting the two LEVEL pots' LUG-3 means you'll have 4 lugs of both LEVEL-pots all tied together (both #3s and #2s), which negates you having switching between LUG-2 of each LEVEL pot since now they're all connected on the PCB via your wiring.

An aside, I almost missed your pot-lug numbering, it's VERY faint, and at first glance I thought you had LUG-3 on one pot wired to LUG-1 of the other.


I previously made a GAIN-POT swapper diagram, I've re-jigged it for you (since the "LEVEL" is more of a GAIN-pot anyway).
You'll need to offboard-wire both pots, and that way you won't have any interactions between the pots.
Also note, there is no connection for MODE switch's LUG-3 in the schematic, so you don't need a wire for it, just leave MODE's PAD-3 and LUG-3 empty.
Mod the LEDs to however you like: one LED, one bi-colour LED, one LED that's either dim or bright ...


View attachment 90938

 

[Feral Feline]

Wow thank you so much for such an amazing response and drawing up a diagram. I didn't even consider that it would be different depending on how the pots are wired, but like obviously it would

I just assumed it could use the same thing that i've done in the past when switching pots, By using this method that i've seen shared around. Since i've used this for for my barbershop and a couple other gain pedals.

View attachment 90955

That works for the Barbershop (and many other pedals, of course) because none of those pot-lugs are tied together on the PCB — anything wired as a Voltage-Divider is good to go. Wired as rheostats, though...


I've re-upped my diagram, 'cause I noticed one of the labels still said GAIN instead of LEVEL.
Gotta expect mistakes when working in my sleep.

 

[DGWVI]

Here's the scheme I use



This will also give you a pole for the Gain pot, and an led