Slight confusion about the Big Muff tone control

[dano12]

I'm doing some research to learn more about the Big Muff tone control. Problem is, that research is leading to a lot of different versions of what is supposed to be the stock control.

Any ideas on how to sort out/reconcile these three versions?







Also, I'm having trouble locating material that talks about where the tone stack should go in a circuit and why. For example, on the Big Muff Pi, it is before the final transistor. On other circuits it is just before the volume pot. Any pointers here?

Much thanks.

[slacker]

Apart from the component values the muzique and ggg schematics are the same, they are just drawn differently. The difference in component values is either because they are from different versions of the big muff or because the values have been tweaked to how the builder liked the sound.
Andys tone stack is different I don't know whether it's supposed to be or if it's a mistake.
The reason for putting a extra amplifier stage after the tone stack is to make up for volume lost by the tone stack and to provide the correct impedance for the tone stacks output. Depending on how loud your circuit is you might not need it.
If you want to experiment with the tone stack download the Duncan's tone stack calculator which is a nice little program that models various tone stacks including the BMP one.

[dano12]

Thanks slacker, you cleared up a few mysteries for me, especially about adding a simple gain stage to compensate for the tone stack volume loss.

[Mark Hammer]

It can look many different ways but a cap in series, followed by a resistor to ground is a highpass filter section, and a resistor in series followed by a cap to ground is a lowpass filter section.  The tone pot simply pans between the outputs of these two filter sections.

I find it interesting the way that the same schem drawn differently can lead to puzzlement about how a circuit works, OR complete clarity about how it works.  It's certainly not meant as a criticism at anyone, but when drawing up schematics for the rest of us, try to lay out the circuit in a manner that allows people to recognize the subcircuits in terms of familiar elements.

[stm]

After careful inspection I must say there is *definitely* a mistake in the way the second circuit is drawn.  The Pot is wired like a volume control, and C1-R2 are shorted to ground.

The first and third circuits differ only in the 22k resistor to ground being 100k.  If you use Duncan's TSC you'll find that varying this resistor canges the notch depth.  These variations have been already addressed by Jack Orman here: http://www.muzique.com/lab/tone3.htm

[Mark Hammer]

He's right.  I gather Andrew meant to draw the pot lug as connecting to the C1/R2 junction and R2 going to ground.  The circit shown would "work", but not at all in the manner intended for a BMP.