Adding Mid Control To Russian Big Muff?

[BrainDrain]

So I'm building the tagboardeffects/layouts version of the Russian BMP. It already has a mid boost switch to add capacitors but I want to add a mid pot too for extra tweaking. Most Russian BMPs look like this to start:

Except the layout I'm using has a 100k resistor instead of the 22k to ground.



The mods say to do this:

Here they replace the 22k with a 3k3 and add the 25k mid pot to ground after it.

So my question is: since the layout I'm using has a 100k resistor instead of 22k would I still use a 3k3 and 25k pot or a higher value resistor and 100k pot?

 

[jwin615]

It's going to depend on the cap values as well
You can plug your values into the TSC here and tweak the resistor value up and down to simulate the sweep of the pot
Choose the big muff tab at the top
(Better achieved on desktop but works on mobile)

 

[BrainDrain]

It's going to depend on the cap values as well
You can plug your values into the TSC here and tweak the resistor value up and down to simulate the sweep of the pot
Choose the big muff tab at the top
(Better achieved on desktop but works on mobile)

Looks interesting but not really sure how to use it. I was told the 3k3 resistor is just to set the minimum value so the pot never goes to 0k. So if I added a B100k pot in place of the 100k resistor wouldn't it be kinda the same as replacing the 22k resistor with a 25k pot like the diagram? Essentially just swapping a resistor with a pot/variable resistor of the same value. Or are you saying the 3k3 minimum value resistor needs to be higher if a higher value pot is used?

 

[jwin615]

The thing to remember is that minimum resistor sets one end of the sweep. Too low and the first half of your sweep may have no effect of be unsuable. Too high and you're missing usable areas of the sweep. I tried following the layout but they give me a headache and couldn't pin down what is going where.
Where the other half of the switch go? it looks like there's 3 caps in there but I can't tell whats up with the 3rd. Sorry, really suck at following stripboard.
TLDR, yeah, your idea will work.
Throwing a 10k-20k trimpots in there to be in series with your mids pot may be advantageous to set the minimum resistance for the circuit.

 

[BrainDrain]

The thing to remember is that minimum resistor sets one end of the sweep. Too low and the first half of your sweep may have no effect of be unsuable. Too high and you're missing usable areas of the sweep. I tried following the layout but they give me a headache and couldn't pin down what is going where.
Where the other half of the switch go? it looks like there's 3 caps in there but I can't tell whats up with the 3rd. Sorry, really suck at following stripboard.
TLDR, yeah, your idea will work.
Throwing a 10k-20k trimpots in there to be in series with your mids pot may be advantageous to set the minimum resistance for the circuit.

Thanks for the info. Didn't realize that it would affect the sweep. So if I were using the 25k pot a 3k3 resistor would be fine but with the 100k pot the resistor needs to be a bit higher? Also does it matter which side the resistor goes on? I've seen people put it on the ground side and also on the side before the pot. Good idea with the trimmer. I'll probably put one on, find the sweet spot and then take it off and measure it, then add the proper resistor.


The switch:
One side of the switch goes to "Sw1" on the board and the other side goes to lug 3 of the tone pot, then lug 3 of tone pot is connected to where it says "tone 3" on the board. So really the switch is just daisy chained to the pot and then to the board. So both caps on the switch can separately be added in parallel with the 4n.

 

[jwin615]

Thanks for the info. Didn't realize that it would affect the sweep. So if I were using the 25k pot a 3k3 resistor would be fine but with the 100k pot the resistor needs to be a bit higher? Also does it matter which side the resistor goes on? I've seen people put it on the ground side and also on the side before the pot. Good idea with the trimmer. I'll probably put one on, find the sweet spot and then take it off and measure it, then add the proper resistor.


The switch:
One side of the switch goes to "Sw1" on the board and the other side goes to lug 3 of the tone pot, then lug 3 of tone pot is connected to where it says "tone 3" on the board. So really the switch is just daisy chained to the pot and then to the board. So both caps on the switch can separately be added in parallel with the 4n.

Order doesn't matter. Series is series.
Could just run a wire to a breadboard, tune it to your liking then tack the resistor and wire onto your pot.
You may find a 1k resistor and 100k pot works fine. Or a 68k and 25k pot. Or a 22k and 50k pot. Nothing is going to be wrong, it's just a matter of what sound good to you. With a little experimentation, you can hopefully get it to a mostly usable sweep.
I'd start with a 5kish and 100k pot and see what you think about the sweep.
If the lower resistance settings of the pot are trash, up the 5k(or tune with a trimpot).