Sallen Key Bandpass Filter for Wah Wah

[mac]

One of the things I like about LTSpice is that I can do virtual breadboarding on the fly withtout burning tubes for hours only to experiment
I ran some simulations using a generic Sallen Key topology adapted for a non-inductor wah wah.
Curves are not exactly as those of a Cry Baby, but the range is wider which can be good for whammy-like sweeps.
It's so wide that it can be used both for guitars and basses.
Q can be set varying R6.
The problem is that it needs 3 or 4 variable resistors, but it can be done easily with LDRs, one led, and a control resistor. Two options, you can set the light of the led with a suitable pot, or you can vary the distance between the led and the LDRs.

Schematic,


4 LDRs,


3 LDRs,


Enjoy,


mac

[Kipper4]

I think I get it. But I have been known to not
So R5 and R6 control the gain
R1 and R2 the freqauncy.
I had a look at the data sheet for the spiced op amp as I'm not familiar with it.
I couldnt see anything that an LM358 couldnt do. I'm guessing the op amp would have to be rail to rail right?
If I'm on the right track (pun intended) I'll be back with more dumb questions Mac be warned.
If not I'll just go straight to the cloakroom.

[mac]

LT1001 is the first opamp in the list, that's why I use it 
Besides simulations run faster. Sometimes I use LT1055 and for more accuracy LT6220, but it takes longer.
In real world, use a cheap LM741, TL071/2, LF351, RC4558 or whatever you have at hand.

You are correct, R6/R5 control gain. And R1,2,4 and C1,2 the frequency.

I couldnt see anything that an LM358 couldnt do. I'm guessing the op amp would have to be rail to rail right?

I used rail to rail in the schematic, but you can use vref=4.5v, and connect R7, C2, R4 and R5 to vref. The volume pot R3 to gnd.
9v -- 47k -- (vref) -- 47k//100uf -- Gnd    works fine.

mac