The Minima Resonant Filter is based on the Mu-tron Micro V envelope filter, designed by Mike Biegel and first released in the mid-1970s as a lower-cost alternative to the Mu-tron III.
The Micro V has a very practical origin story. The original Mu-tron Phasor (now referred to as the Phasor I) used CA3080 OTAs for the phase stages. When this was discontinued in favor of the more popular Phasor II, the company had a lot of surplus CA3080 chips and no active products that used them. At the same time, they realized they didn’t have any low-cost pedal offerings. The Micro V was designed with the goal of filling both needs.
The end result is a similar effect to the Mu-tron III, but with a completely different circuit topology. It was discontinued in 1980 along with the other pedals in the Mu-tron lineup not long after the company’s sale to ARP.
The Minima is a slightly expanded version of the original Micro V circuit. The two fixed resistors that set the attack and release of the envelope detector have been made variable, and we’ve added a third in-between position to the “Hi/Lo” switch. It also replaces the CA3080 with the LM13700 (or the equivalent NE5517), which performs identically but is much easier to find.