Help me understand my tone stack and how to connect it

[Ben Lyman]

This is the "Gus Tone Stack" I have put in my own fuzz circuit. I have it on the breadboard and when I turn it ccw it cuts the highs like it should, cw increases treble. Sounds great and I can figure it out only by trial and error, swapping the pot leads 1&3 until it operates correctly.
Can you look at my schematic and tell me which way is ccw and which way is cw according to the way the caps and resistors interact?

[mth5044]

A "Gus Tone Stack" you say? Looks like a Big Muff tone control with some different values to me. One side is a low pass filter and the other side is a high pass. The pot blends between the two. If you can identify which is which, you should be good!

[Ben Lyman]

Thanks, that's what I mean by "help"  I can't identify what side does what.
Gus recommended it to me for this particular fuzz, so ya... "Gus Tone Stack"
Just giving credit... you know... so he doesn't "come after me"   

I just thought of a way to rephrase my question:
If you look at my schematic's variable resistor and call one side "LEFT" and the other side "RIGHT"
Which side is CCW and which is CW?

[idy]

As you turn to the "left" of the schematic you are getting close to that .01u cap, the one letting highs through. As you pan to the "right" you are getting close to that .01u cap going to ground, letting all the highs go down the drain. So the terminal to the left in your schematic, if you want it to function like a Big Muff is pin 3 of the pot, the "trebly" side, turning clockwise. The terminal on your right in the schematic would go to pin 1, so you get all bassy when you turn it CCW, "down."

[PBE6]

I think what mth5044 is hinting at is that if you can identify what each signal branch does, the answer is straightforward.

A series cap followed by a resistor to ground forms a HP filter, and the reverse forms a LP filter. Connect the LP filter to the fully CCW position and the HP filter to the fully CW position and the knob will act as you've described. Whatever side you point the wiper to will be the prominent signal at the output.

[Ben Lyman]

Perfect answers, one and all, thanks!
Now I have to remember,
series cap + res to ground let's highs pass thru.
series res + cap to ground let's lows pass thru.
I think I got it. Thanks again!

[mth5044]

Thanks, that's what I mean by "help"  I can't identify what side does what.

I think what mth5044 is hinting at is that if you can identify what each signal branch does, the answer is straightforward.

Exactly. I was trying to lead you to typing lowpass or highpass into google, which pops up an image without even asking for it. Sometimes it's faster.

[Gus]

mth5044
Yes a BMP like tone control it is the values I like in some circuits. I posted the values in a thread about one of my fuzz builds.
I think Ben was being polite and noting where the values came from.

[mojokorn]

Perfect answers, one and all, thanks!
Now I have to remember,
series cap + res to ground let's highs pass thru.
series res + cap to ground let's lows pass thru.
I think I got it. Thanks again!

This is a great site to help calculate the cutoff frequency...

http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

Also, Fc = 1/(2*pi*R*C) is sometimes easy to calculate with approximation.

Looking at it at 1/(6*Rbasevalue*Cbasevalue), then adding the C and R exponents, and reversing the sign for the final calculated value is a cool trick.

Once the value current Fc is calculated, you can use up-down thinking to get new values.  For instance, doubling either the R or C will cut the Fc by half, and halving the C or R will double the Fc.

Hope this helps.

[bluebunny]

Now I have to remember,
series cap + res to ground let's highs pass thru.
series res + cap to ground let's lows pass thru.

Rather than remember this by rote, remember instead that a capacitor blocks DC, but lets through progressively more AC as the signal frequency increases.  Then look at where this capacitor is going.

If it's going to ground, then it's letting progressively more highs disappear to ground: it's a high-cut filter (or low-pass).  If it's in series with your signal path, then it's letting progressively more highs through to whatever comes next: it's a high-pass filter.  The frequency at which this action happens is determined by the resistor and capacitor values as mentioned previously.

[GibsonGM]

Now I have to remember,
series cap + res to ground let's highs pass thru.
series res + cap to ground let's lows pass thru.

Rather than remember this by rote, remember instead that a capacitor blocks DC, but lets through progressively more AC as the signal frequency increases.  Then look at where this capacitor is going.

If it's going to ground, then it's letting progressively more highs disappear to ground: it's a high-cut filter (or low-pass).  If it's in series with your signal path, then it's letting progressively more highs through to whatever comes next: it's a high-pass filter.  The frequency at which this action happens is determined by the resistor and capacitor values as mentioned previously.

Sure, or look at "cap in series, letting highs pass"....HPF

"That cap is going to ground, in SHUNT, sending the highs to ground..."    LPF

You'll get used to it

[mth5044]

mth5044
Yes a BMP like tone control it is the values I like in some circuits. I posted the values in a thread about one of my fuzz builds.
I think Ben was being polite and noting where the values came from.

I thought pointing out where the topography came from might help OP understand connections - didn't mean to slander your name or anything!

[Gus]

mth5044

No issues with your post. I just wanted to be clear it is a set of values I like in a BMP type control.