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WAH on Telecaster

StromTele

New Member
Looking at constructing a fixed (cocked wah) tone control with an passive RLC circuit, (employing the obvious inductor).
 
Push /pull logarithmic tone pot
 

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OK, then a parallel resonant LC circuit tuned to the wanted frequency, connected across either the pickup to volume point or the final output of the guitar, via the push-pull pot switch.
(What guitar would you be adding it to? Tele in your name is probably bit of a giveaway? That's one type I do not have..)

A section of a pot in series with the switch could adjust the depth of the cutoff either side of the peak.

What frequency (or string/fret) would you want it centred on?
 
For info, an LT700 audio transformer is nominally 550mH on the high impedance winding. They are 16x16x20mm, readily available and cheap. (Ignore the other winding).

With a 0.47uF in parallel, that gives a resonant frequency of ~313Hz, very close to an open high E string at around 330 Hz.

The frequency changes with the square of the capacitance change; using 1uF makes it around 215Hz, or 0.1uF gives 679Hz.

(Assuming the inductance and capacitance are in tolerance).
 
The frequency changes with the square of the capacitance change;
I think that you mean square root of the capacitance change.
Looks like a typo, your numbers are OK.

JimB

(Or, should I say the reciprocal of the square root of the capacitance change.)
 
OK, A 68nF would give around 823Hz, or 56nF 907Hz

Because of the possible component tolerances, I'd probably try a 47nF then add 4.7 and/or 10nF caps to bring it down to the sound you like.

You could possibly use the changeover switch to swap from the fixed tone cap to the tuned circuit? It would then become depth rather than tone.
 
Excellent ! Thanks. Could you sketch out a couple workable RLC schematics for the push-pull?
I think the down position of the pot would just be something like 0.022 as a base brighter sound. Thanks, Marc
 

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