Mu-Tron Micro V

The Mu-Tron Micro V is an envelope-controlled filter pedal from the mid-1970s, built by Musitronics as a smaller and cheaper alternative to the company's landmark Mu-Tron III. Like the III, it is an automatic wah: instead of rocking a footswitch, the pedal follows the volume shape of what you play and sweeps a filter in response, so the sound opens up as you play harder and closes as you back off. Musitronics described it as delivering "the touch-controlled wah effect pioneered by the original envelope follower, Mu-tron III"¹².

The Micro V was discontinued in 1980, along with the rest of the Mu-tron lineup, not long after the company's sale to ARP². Original units are vintage pieces, though the circuit has lived on in replica kits from other builders.

What it does to your sound

The Micro V is an envelope follower driving a voltage-controlled filter. The filter's peak response frequency varies with the envelope of your input signal, which is what produces the automatic wah effect: pick hard and the filter sweeps wide, play gently and it barely moves. Guitar World describes the Mu-tron approach as optocouplers responding to playing dynamics to sweep an EQ filter, "resulting in a funky wah sound" that is expressive and responsive⁴.

Musitronics advertised the Micro V's two controls as allowing "a wide range of effects suitable for a funky bass guitar, a screaming lead guitar, or anything in between," including electric keyboards and electrified wind instruments¹. That makes it one of the more instrument-agnostic pedals of its era, and the Hi/Lo range switch is what lets a bass player keep the sweep in a useful register.

Controls and connections

The control set is minimal compared with the Mu-tron III:

The enclosure is described by the maker as "a very compact and rugged housing of painted steel and heavy-gauge aluminum"¹, and at 1 pound it is a genuinely small box for its era.

Specifications from Musitronics¹:

Power

Power comes from an internal 9-volt battery, not included with the pedal. An optional external 9-volt AC adapter can be connected through a mini-jack on the unit¹. Note that the mini-jack is not the center-negative barrel connector found on modern pedals, so powering an original unit today takes an adapter to suit.

How it differs from the Mu-tron III

The Mu-Tron III, designed by Mike Beigel and released in 1972, was the original envelope follower and voltage-controlled filter that produced automatic wah effects changing timbre in response to playing⁵. The Micro V carries that lineage in a stripped-down form: two controls instead of the III's larger panel, a smaller steel-and-aluminum enclosure, and a lower price.

According to Aion FX's technical history, the Micro V was designed with two goals in mind: to use up surplus CA3080 chips left over after the Phasor I was discontinued, and to fill a gap in Musitronics' lineup for a low-cost pedal². The CA3080 is a transconductance amplifier that was central to how these voltage-controlled filters swept.

The family resemblance is recognized by builders today. General Guitar Gadgets sells a replica kit of the Micro V and says it gets "some of the same sounds as the Mu-tron III"⁶, and Jed's Peds offers a Mewtron Micro V kit described as an auto wah filter effect that "compares to the Mutron Envelope Filter," with a toggle switch added for extra variety⁷.

Where it came from

Musitronics was founded around the Mu-tron III and became known for a range of effects including the Bi-Phase, the Flanger and Phasor, the Vol-Wah, and the Mu-tron III³. The Micro V arrived in the mid-1970s as the lower-cost entry in that line², advertised in original Musitronics ads from the 1970s¹.

Mike Beigel designed both the III and the Micro V. Looking back, he has been candid about how the smaller pedal fit the company's plans⁵²⁸:

Mike Beigel, in a Premier Guitar builder profile on the Mu-Tron story⁸

The pedal was discontinued in 1980 along with the other pedals in the Mu-tron lineup, not long after the company's sale to ARP². Its origin was practical in another way too: it was designed to use surplus CA3080 chips left after the Phasor I was discontinued, and to fill the company's lack of low-cost pedal offerings².

The Micro V's place among compact Mu-Trons

The Micro V itself came out of a practical problem: it was designed to use surplus CA3080 chips left after the Phasor I was discontinued, and to fill the company's lack of low-cost pedal offerings². That made it the low-cost entry in the Mu-tron lineup, and when the company was sold to ARP the whole line, Micro V included, was discontinued in 1980².

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