My son , the guitar player told me that the Wah using an inductor controlled by a pot on a swinging pedal so called "Classic " original was the best sounding one .
I tried to find an old one to experiment with but to no avail , even an old style in good working order is cherished by the holder and to acquire such a unit would go for more than the original price .
As I was mostly interested in the working mechanic of such a pedal I eventually found a like new second hand pot controlled volume/boost pedal made by Dunlop for a reasonable price . After much searching I found in my junk box a small output transformer with the right induction range required for the application . I stripped the pedal of its innards then proceeded to build the so called original Classic "Wah Cry Baby" circuit I found on the web and assembled the lot in the pedal . The existing volume control value in the pedal was measure at 500K ohms and decided to use it although the wah circuit called for 100k ohms pot .
I must admit that it sounded smoother than other control types but after a while also a bit dull , so I further continued experimenting with the circuit and added a few modifications to make it much more flexible without affecting its basic caracter , below is the modified circuit .
The following are the modications made to the original circuit
1- Q1 and Q2 are now a 2N2222 NPN and VR1 was added to vary the gain of Q1 if required without changing its bias . VR1 is a miniature trim pot on the circuit board to allow setting the gain to suit the guitar pick-up output .
2- R6 and VR2 were installed to vary the resonnance range of L1 , the result is from soft to full .
3- S1 switch ( SP3P ) was added to enable more ranges of wah by selecting three capacitors .01uF , .02uF, .03uF to cover a wider guitar range and effects .
4- I have retained the 500K ohms volume control , as , in my opinion it compensates for the short travel of the pedal control , and I found that the pedal action for a slow to a fast wah effect is shorter .
5- The inductor as I indicated is small output transformer rated at 1K or more to 8 ohms impedance , I estimated the unductor value to be between 400 and 500mH and worked very well . As shown on the layout both windings added in series were used for a bit more inductance as indicated by the note " see text " .
Most of the old Wah style pedals use the same basic circuit that I started with , that is without the modification detailed above and for those fortunate to already own one of the venerable Wah unit , it would be a very simple undertaking to modify your existing circuit by tracing and locating the points where to insert the modifications without much trouble .
Layout and PCB shown is trwice the size .
Below is the same Wah circuit modified to be controlled by anormally open push on/off switch using an LED/LDR module to active the wah . The effect is similar to the wah described on the first page and sounds very good but without the advantage of controlling the wah action as with the flexible pedal control .
VR2 is used to adjust the LED brightness from soft to hard activation.
Layout and PCB shown is trwice the size .
The Running Wah
I called it the Running Wah because it is alway on and should be used with a by-pass switch .
For this circuit I made use of theTwin-T oscillator . The sine wave produced by this oscillator lends itself well to produce a smooth running wah effect .
RV1 controls the speed and RV2 controls the intensity of the wah effect . Hitting a note in the mid-cycle of the wah effect at slow speed produces an interesting effect . At the higher speed something like a warbling effect is apparent . I thought it might interest those who would like to experiment with this concept and do away with foot control except for a by-pass switch .
A N-FET is used as a variable resistor connected between the "common" bus from pin 3 of the op-amp and the junction of the two phase shifting capacitors C6 an C7 in the op-amp by-pass path in parallel with R12 the gain resistor .
To correct mistakes the layout graphics have been completely revised . As suggested by a Hobbyist C9 has been added as an option to increase resonance , the value can be .2uf to 1uf .
The range of the oscillator cannot be altered by changing the value of RV1 but a different range can be by switching in different but equal values for C1,C2,C3 by using a 3PDT switch ( Three poles Double trow )
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