TUTORIAL PedalBlock Tone Control - Gimme All The Muffs!

[BuddytheReow]

This is a stupid simple build and IMO one of the most efficient mods given the number of parts this takes. This mod can be done on countless circuits, especially one-knob fuzz pedals. Some of my more recent posts have been talking about tone filters/controls. Here's an extract from one of them.

Low Pass Filter - anything below a certain frequency determined by the combination of values for the resistor and capacitor will go through the circuit.
High Pass Filter- anything above a certain frequency determined by the combination of values for the resistor and capacitor will go through the circuit.

Not that you know a little "theory" let's talk about the PedalBlock Tone Control. Here's the schematic and the build doc.

https://docs.pedalpcb.com/project/PedalBlocks-ToneControl.pdf

This is literally the Big Muff Pi tone control skeleton. Compare the two pictures above. Can you tell which is which in the schematic? C1/R2 form a high pass filter and R1/C2 form a low pass filter. The 'TONE' potentiometer merely blends the two together. Clockwise is more treble and CCW more bass.

Here is what it looks like on my breadboard. EDIT: I have tried to make my breadboard look as close to the schematic as possible. The white jumper on the left is my output. The yellow jumper (yes, it's yellow. My camera/lighting sucks) is on the right and my input.




2 things need to be mentioned about this:

1. It is a passive tone filter. It requires no power and dumps all the unwanted signal to ground. This means that it will suck out some noticeable volume. The simple fix is to put a booster circuit block after it as a recovery stage. If you've wandered around forums wondering what is a recovery stage, it's usually just a booster.

Edit: I would recommend starting here. https://forum.pedalpcb.com/threads/...toboard-start-here-lpb1-some-dirty-mods.8354/

2. Depending on the values you use for the components there will be an EQ notch. The original BMP had a noticeable mid scoop sound because of this tone stack. Google it if you're interested in looking at all the EQ curves to prove it.

Want a Civil War tone knob or Ram's Head? Check the build doc! Here are the values for the components. Of course, experiment with different values to find the tone "window" that you like.


BuddyTheReow

 

[music6000]

I used the PedalPCB PedalBlock Tone Control pictured below as I needed the clearance under the standard PedalPCB Board with Right Angle 16mm Pot.
In this scenario, I used a 12mm Pot as it was right beside a 4pdt toggle switch.

 

[Feral Feline]

Low Pass Filter - anything below a certain frequency determined by the combination of values for the resistor and capacitor will go through the circuit.
High Pass Filter- anything above a certain frequency determined by the combination of values for the capacitor and resistor will go through the circuit.

 

[jeffwhitfield]

Weird thought…I wonder if this could be used directly on the tone knob of a guitar. Could it work? Or does it require an active circuit? I’m guessing some sort of onboard active electronics would be required.

 

[fig]

Weird thought…I wonder if this could be used directly on the tone knob of a guitar. Could it work? Or does it require an active circuit? I’m guessing some sort of onboard active electronics would be required.

Sure it'd work. It's passive.

 

[almondcity]

my question is this: what determines the value of the pot for this? what does changing the value do?

 

[BuddytheReow]

my question is this: what determines the value of the pot for this? what does changing the value do?

My lazy answer is try it and find out on your breadboard! I don't have this ready to go on my board right now to experiment, but I will speculate here. 100k is pretty much the standard for Muff tone pots with a handful of exceptions. The purpose of the pot is to alter the resistance between the two tone filters to the output. Increasing the pot will have a harder cutoff between each filter. Lowering the value will have more "blend" between the two.

 

[daeg]

Weird thought…I wonder if this could be used directly on the tone knob of a guitar. Could it work? Or does it require an active circuit? I’m guessing some sort of onboard active electronics would be required.

It will work, at the cost of a huge drop in volume, and an unpredictable response due to the high impedance and complex impedance of guitar pickups.

If you're unfamiliar with this stuff, try playing around with the Duncan Tone Stack Calculator: https://www.duncanamps.com/tsc/download.html
A BMP style tone control will work as expected if the source impedance is low and mostly resistive. Guitar pickups are neither of those things, by a long shot.

That said, if you put a buffer / boost in your guitar as well you could drive this circuit, no problem. At that point, you'd need to ask yourself "Do I really want a huge mid-scoop in my guitar?"

 

[jeffwhitfield]

It will work, at the cost of a huge drop in volume, and an unpredictable response due to the high impedance and complex impedance of guitar pickups.

If you're unfamiliar with this stuff, try playing around with the Duncan Tone Stack Calculator: https://www.duncanamps.com/tsc/download.html
A BMP style tone control will work as expected if the source impedance is low and mostly resistive. Guitar pickups are neither of those things, by a long shot.

That said, if you put a buffer / boost in your guitar as well you could drive this circuit, no problem. At that point, you'd need to ask yourself "Do I really want a huge mid-scoop in my guitar?"

I think the answer to that last question, if you’re Frank Zappa, then the answer is “Yes!” I think he actually did put a buffer with a Q-based filter in one of his guitars. Weird setup…but he liked the ability to tweak the frequency on the fly to cut through the mix.

 

[daeg]

Do you mean the Systec Harmonic Energizer? That one is actually a parametric mid boost.
https://www.pedalpcb.com/product/zapper/

 

[Coda]

I don’t think Zappa ever had the Harmonic Energizer in a guitar. It would be off stage, and someone would sweep the pot as he played. The Green Ringer, on the other hand…

 

[cdwillis]

A while back I made a little vero board layout that you can solder directly onto a pcb mount pot to put into pedals without tone controls. Could be handy for trying different tone controls on a breadboard as well. I used the more scooped Rams head values, but it's easy to change them to the other versions. I like the 33k/10nf 3.9nf/33k a lot, and the Russian stack.

 

[Tomnyhc]

Thanks for this! Your posts have been very helpful!