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

1. Hamuro Envelope Detector Circuit with Separate Attack and Decay Settings
2. Automatic Wah/Quack Effect Using LED+LDR Controlled Band-Pass Filter