From the VFE website:
The MINI MU is derived from the classic Mutron III envelope filter (aka autowah), and has all the same great fat and funky filter sweeps inside a much smaller box. A few extras have been added, namely an active clean gain stage and an “in between” position on the range switch. With the included charge pump, the MINI MU runs on +/-9V like the original without needing a special power supply or two batteries.
HOW THE MINI MU CAME TO BE
I started tweaking with the Mini Mu after continual requests for an autowah, most frequently one based on the original Mutron III pedal. The original design was a straight-up clone with a volume control added. Countless tweaks followed, all of which were attempts to smooth out the filter’s response, add headroom, and increase versatiliy - each tweak came from either user responses or my own personal testing.
The Mini Mu is great at adding quack & funk to your tone. However, don’t look here if you want slow filter sweeps. The Mini Mu utilizes optocouplers with a faster reaction time, which was key aspect of the custom units used in the original circuit.
LEVEL: We added a clean boost to the end of the circuit, giving you full control over the volume, from off to to 20dB of gain.
GAIN: Sets the pre-gain before the filter. This also affects the sensitivity and range of the filter sweep. We modified this section to provide the most clean headroom possible.
PEAK: Adds feedback, giving the filter more bite and resonance to the autowah’s sweep.
DRIVE: Sets the direction of the filter sweep. Up = starts low and goes higher, Down = starts high and goes lower.
MODE: Sets the type of filter. HP = high pass (brightest), BP = band pass, LP = low pass (fattest).
RANGE: Sets the overall frequency range of the filter sweep.
INTERNAL CONTROL: The internal trimpot on the main board tunes the sensitivity of the optocouplers. Use this control to add sensivitity or tune the filters frequency response.