Not Just a Phase - Mu-Tron Bi-Phase Clone By PedalPCB

As I'd mentioned in my previous blog entry, I hadn't built many modulation pedals recently, and I figured it was time to remedy that. This is one I'd had going in the background for a while, but given the size and uniqueness of the build, I had to order additional parts and bits to actually make it happen. Based on the vintage Mu-Tron Bi-Phase, the PedalPCB Duo Phase an involved build, but in some ways is on the easy side for a modulation pedal - more on that in a bit. The Bi-Phase pedal itself, is a vintage unit that's found its way on both synths and guitars alike. Originals are long out of production, and vintage units run for quite a bit of money these days. There are apparently Chinese copies out there, but even those aren't exactly cheap.

Technical expert Steggi posing with her handiwork

The first part of this build was straightforward, if involved, as I was just populating the PCB. The Duo-Phase has two copies of the same circuit on the board - with few extra components in the middle. The biggest challenge is the sheer volume of components - nearly 100 resistors, almost 40 capacitors, and 15 integrated circuits! Although this is a vintage pedal, I stuck with newer components, so the resistors are all 1% metal film 1/4W (mostly Yageo), the film capacitors are a mix of Kemet and Panasonic, and the ICs are all new production TL072IP and TC1044SCPA - all of which are socketed. The biggest challenge comes in building the six stage optical phasor circuits. Unlike my previous multi-stage optical phasor build (the AionFX Quadratron clone of the Lovetone Doppelganger) which has four separate depth/rate LEDs, each side of the Bi-Phase has six stages coming off of one depth/rate LED. That means you have to carefully position six LDRs (light dependent resistors) around each LED. It also means you pretty much have to test the pedal while it is enclosed or in a very dark room!

Once the PCB was populated, I decided to modify my build process a bit for the jacks as this pedal has an option that I'd never used before. My previous combo pedal build (a Lovetone Cheese Source clone) uses a single set of input / output jacks because I decided to incorporate an order reverser. One version of this pedal just uses a single input and single output jack, but there is the option to have the pedal split. In other words, both "sides" have their own input and output jacks. It did, however, require my sourcing the correct switched input jack so I could use the pedal in single in / single out configuration without having to run a patch cable from one side to another. Since this was my first time using that particular 1/4" jack, I went ahead and built up the jacks, tested them, and then attached their ground wires to the PCB. The upshot of this order of operations is I'm able to shorten the ground connections from the jacks to the board, so I may start doing this on any pedal where I'm actually grounding the jacks to the board (as opposed to a star ground on the input).  

I ran the input / output wires to the ends of the enclosure. Some modulation pedals tend to pick up noise from op-amps or the modulation circuitry, and I wanted to make sure the signal coming out of the unit was as clean as possible. Because I'd pre-wired the jacks, I was able to minimize the lengths of the wires while still being able to wrap all of the connections in heat shrink tubing. The end result being perhaps one of my cleanest wiring jobs ever.

For the enclosure, I decided to draw inspiration from Leonardo da Vinci - so instead of Steampunk, I sort of have "Da Vinci-punk." The text all uses a font that emulates da Vinci's handwriting. One side mirrors the other, and I decided to throw in that detail because da Vinci himself actually always wrote backwards. 

The trimmer pots on the PCB are there to help you adjust the brightness at full on and dimness at full off on the LEDs. It didn't take much tweaking to get them dialed in, and once I had the enclosure suitably dark the sound of the pedal is absolutely amazing. The only drawback I see is the pedal is a bit large, but I'm sure it will see use on my board as the dual in/out jacks provide a lot of flexibility.