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MUTRON Biphase Clone



The Mutron Biphase is a legendary (bi)-phasor pedal, made by Musitronic's around 1975/76... It's a 12 stages or 2*6 stages optical phasor and one of the best i have ever heard. I have repaired many of them. Also one day of 1996, i have cloned it. I have redrawned schematics from original pcbs of a vintage Mutron Biphase and assembled the prototype in a 1U rack.

The clone is an exact copy of the original for audio part and sweep generators. The difference is on led modulation drivers, where original circuits have been replaced by a calibrated  CV input and a scale/offset stage for a larger adjustable range.

Why did i change LDRs & drivers? Because to find same as vintages ones is almost impossible :3 double LDR + led , all encapsulated in a little metal can... I have found 6 dual cells in two dead MXR100 guitar pedals. Let's transform "noisy" MXR100s in a cool Mutron Biphase....I have soldered 3 dual LDRs on a 14 pin dip socket, this way i can test differents cell+led assembly and compare...It is also possible to use simple LDR but placing them around the led is more complicated..LDRs+ led must be perfectly isolated from ligth, otherwise effect is impossible to trim. For aop, originals are RCA4558, many other dual aops will work well too (TL072,LM358,etc...). Resistors are 1% metal on audio path, 5% metal otherwise, capacitor on phase stages are polypropylen. This is for my clone, but original Mutrons were builded with carbon 10% resistors and classic polyester capacitors.This slightly changes the sound color ...

Cloned  cell unit with MXR cells
Audio pcb of the clone

Controls are the same as the Mutron simply added a pot equivalent to"pedal pot" on original Biphase ( it was an external pedal unit ). This pot allow a manual control of  phasors, like the cutoff on a vcf also very slow modulations can be reach using it. An external CV modulation input for each phasor stage has been added.

And sounds ?  Fat and musical phasor effect is present  same as the vintage, but with a sligthly larger sensitivity sweep....Like the original, the noise floor is very low .


Last update 10/2007

© Marc BAREILLE 2002,2007