Mutron Bi-Phase

Mutron Bi-Phase Frontview

Mutron Bi-Phase Frontview

Repairing a quite battered Bi-Phase.

Turned out that this rather obscure Opto-Electric device (Vactrol) didn’t work properly anymore, here a couple of shots of the dismantled thing and how I fixed it.

Unfortunately the original knobs are no more part of  it and replacement is hard to get and expensive. For now, it has to work with the ones which are fitted.

I also added a new transformer for 240VAC to the device and build a new bypass/pedal switch as I did not have the original one.

Mutron upper PCB

Mutron upper PCB

Bi-Phase Lower PCB

Bi-Phase Lower PCB

The photoresistors of the phasing circuit are placed in the two cylindrical components on the lower pcb.  As one photoresistor seemed defective, I opened up one of these devices. Let’s have a look:

Canned Photoresistors

Canned Photoresistors

Metal can removed, LED and 3 LDR's visible

Metal can removed, LED and 3 LDR's visible

One of these LDR’s was defective, I replaced it by some LDR I found at my local electronic parts dealer and the phaser works. I cannot tell the difference between the right channel with the original vactrol and the channel with the replaced LDR which is good enough for me.

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