Get the Funk Out - Cloning the Legendary Mu-Tron III

The Mu-Tron III envelope filter possibly more than any other pedal created the funk sound of the 1970's. Classic units are in high demand and cost in excess of $600 for units in good shape. The circuit itself is another one that is hard to clone because there are some specific parts required. Madbean pedals used to make a couple of PCBs - the Naughty Fish and Nautilus - that captured the sound of the original pedal. Unfortunately both of these are currently out of production. However, Fuzz Dog now offers the Moo Tron (see what he did there?) board which combines the features of the original Madbean boards to  replicate the effect of the original Mu-Tron III. 

The Fuzz Dog board is well laid out and very clean overall. Despite this being a vintage effect, I ended up using new production components across the board for the build - well, mostly. The resistors are all medal film 1% tolerance (Yageo). The film capacitors are a mix of somewhat classic Panasonic and a few Kemet. The electrolytic capacitors are all Nichicon. I'm using three new TL072IP op amps and a new TC7660S for the ICs. The heart and soul of the unit is, however, the VTL5C3 vactrols. According to Fuzz Dog, nothing else they've tried gives the same results. Fortunately I was able to source some new production ones from XVive. The board includes a polarity protection diode and power smoothing capacitor, but the build sheet recommended jumpering both the diode and the capacitor slots to increase the voltage available to the circuit. I went with Fuzz Dog's recommendation since once I get it wired up it is unlikely that it will ever see reverse polarity.

Populating the PCB was straightforward, but unfortunately getting the unit to fit into the enclosure was far more tedious. The challenge stems from the fact that you have four potentiometers, two DPDT switches, and a 3P4T rotary switch all soldered to the board. The 3P4T rotary switch is just thick enough to cause issues in trying to set the potentiometers and toggles. I had to completely forego any of the washers on the rotary switch (only using the washer that sets the number of "clicks" available on the switch) - and the potentiometers still barely made it through the board. 

As I hadn't gotten the 3PDT daughter boards from Fuzz Dog to go with this build I went with the new ones I'd had made up based on the Drunk Beaver design. I decided to not go with a dimmer switch on this one and went with a standard 4.7K Ohm current limiting resistor for the LED. I did have to flip the LED and ground leads on the ribbon cable, but otherwise the two boards lined up perfectly. The Moo Tron PCB also provided very well spaced input, output, 9V+, and ground pads, so I ended up running all of the jack connections to the board. All of the jack connections are insulated with heat shrink tubing.

For the enclosure, I wanted something fun and slightly out of the ordinary, so the mascot for this pedal is the Hallucigenia. According to Wikipedia:

"Hallucigenia is a genus of Cambrian animal resembling worms, known from articulated fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. The generic name reflects the type species' unusual appearance and eccentric history of study; when it was erected as a genus, H. sparsa was reconstructed as an enigmatic animal upside down and back to front. Hallucigenia was later recognized as a lobopodian, a grade of Paleozoic panarthropods from which the velvet worms, water bears, and arthropods arose."

The background was originally supposed to be a lot more textured than it came out to be on the final enclosure - and I'm still unsure what happened as the art in Illustrator looks fine. I will likely redo the art for future builds, but "Hal" came out looking great regardless!

As to the sound of the pedal, all I can say is WOW. This thing goes so many places, you could play it for an hour and still not cover the complete gamut. I'd built this pedal by request, so hopefully I can get my friend to do a proper demo of its capabilities.