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Modifying The Mu-Tron Bi-Phase | |
For Control Voltage InterfacesArticle from Polyphony, February 1978 |
Those of you who keep up with the various new processing items that are available commercially will recognize the Bi-Phase which is manufactured by Musitronics of Rosemont, New Jersey. This is one of the more elaborate of the hundreds of phasors which have been put on the market over the past two or three years. It features two independent phasors which can be run in series or parallel, and swept with your choice of waveforms. Despite the physical size and array of front panel controls, this unit is easy to modify so you can tap into the internal sweep oscillators or feed your own sweep signal into the phase shift line. There are even two unused holes in the rear panel of the Bi-Phase which are the perfect size for mounting the 1/4" jacks required for the interface!
Mu-tron has a voltage producing photocell pedal as an optional accessory that can be plugged into the footswitch jack (5 pin DIN type connector). It puts out 0-5 volts peak-to-peak, and it will provide higher center sweep (if the Bi-Phase's switches are so set) or more rapid LFO oscillation (see owners manual for getting these effects) as voltage is increased. The trick is to take advantage of the fact that the DIN plug on back has both a voltage send and receive terminal for that pedal, and tap off that control voltage input and wire it to a jack instead.
The reason you can't just "plug in" to that DIN jack is because both of the footswitches provided stock with the Bi-Phase must be plugged in and "on" (so the LED's are "on") for the phasor to operate. So leave the DIN jack alone, you'll still need it.
Before beginning the modification, remember that altering a unit such as this will most always void your warranty from the manufacturer. If that's OK with you, then here we go. Internal access is made by removing the 3 phillips head screws in the front lip of the case, the 4 screws on the top (front panel), and the 4 screws on the rear panel. The green wire in the DIN plug is the control voltage input for the phasor. One can verify this by experimentation if you wish to double check it. Solder a wire to this DIN jack terminal, and connect the other end to the "hot" connection on a 1/4" phone jack. Mount the phone jack in one of the available rear panel holes. This jack will be grounded by virtue of the fact that the case is already at ground. Thus, no ground wire will need to be connected to the jack unless you wish. In this case, the power supply is in a separate section, and is not far from the rear panel. A good solid grounding point can be found there.
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Feature by Jim Riter
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