Maxon AF9 Auto Filter - PEDAL ENVELOPE FILTER FOR GUITAR

(This text is machine translated) The AF-9 is Maxon's version of the venerable Mu-Tron III envelope filter circuit. The biggest difference between the two circuits is that the AF-9 runs on 9V power while the Mu-Tron runs on 18V. In addition, the Mu-Tron III had a Gain potentiometer that controlled the pedal output level and the filter threshold - this was an inconvenient design, as it prevented you from increasing the filter sensitivity without increasing the pedal output volume. Aside from these elements, the basic structures of the two circuits are very similar. The AF9 starts with a unity gain op-amp and then divides the signal into control and effects circuits. The control circuit is modeled by the Sensitivity potentiometer and amplified by an operational amplifier. This control signal then travels to a series of two photocouplers. The affected part of the circuit split goes into a three op amp filter network, almost identical to that of the Mu-Tron, up to the Low Pass, Band Pass and High Pass switches...