Automatic Wah/Quack Effect Circuit with Attack and Decay Control
To get various characteristic of an auto wah/quack effect, we need a flexible control of the envelope detection characteristic. Some playing styles need slow attack but fast decay, but some others don’t. Employing the envelope detector circuit presented in our previous article [Ref 1], but with some modification to make it single supply operation. Here we present the improvement of the previous simple autowah circuit [Ref 2] to accommodate the envelope’s attack/rise time and decay/release time adjustments.
In the schematic diagram of the circuit (Figure 1), we can see the circuit uses two LM324 operational amplifier integrated circuit chips, contains 8 operational amplifiers units in total. The supply voltage is 9V, a common power supply in the guitar effect chain.
When we look at the envelope detector section (U2B, U2C, U2D, and U1D), we can see that we have converted the original envelope detector circuit into a single supply operation by connecting all previous ground reference into a adjustable intermediate voltage level U2A output as the virtual ground point. The voltage level of this point is adjustable by controlling the VR5 potentiometer, and this control serve the offset function of the envelope detector.
Another modification is he gain part of the envelope detector U1D. For this application, the detector gain is set to 11x by R9 and R9. The reason behind this modification is for accommodating range adjustment by VR2 potentiometer. Now with all the integration and modification, this autowah pedal has full controls of range, offset, attack, and decay. About how it sounds, you can be seen in the following Youtube video:
REFERENCES
Hello
What model of LED+LDR (R16) you recommends?
hi do you have pcb?? thank you!!
Sorry we don’t have it… do you think many builders would be interested to buy if we sell it in my webstore?
Great circuit, however I’d not use the ground symbol for your virtual earth as is could be misleading.
I really like the idea of the adjustable attack and decay.
I’m guessing most LDR’s would work as they tend to have a range of 10M+ when dark and down to only a few 10’s of Ohms when brightly lit.
I’ve see a nice feature on an old Mutron 3:- Selectable drive direction.
Ususally auto wah goes low to high but if you include a second LDR with the opposite characteristic of the first and make it selectable you could achieve this.
1st being photo conductive, the second being photo resistive.
C6 and C7 could be replaced with 1 multi-layer 470nf cap?..
Thanks, we need more like you!..