Vintage MXR Phase 45 Info Needed.

[zombiwoof]

I have the Dunlop MXR Custom Shop Phase 45 reissue, but I am looking for a vintage MXR version on Ebay.  What I want to know is if the feedback circuit was added to the original Phase 45 pedals when it was added to the Phase 90, during the block logo period.  If so, what year did that happen?.
Thanks,
Al

[zombiwoof]

No one here knows about circuit changes in vintage MXR Phase 45 pedals?.
Al

[Mark Hammer]

You can't really have a feedback path with a 2-stage phaser like the P45.  To avoid signal-phase issues, the feedback path needs to be an odd number of stages.  And in the case of a 2-stager, that means the 2nd stage would send its feedback to itself.

That said, some FX that use feedback send it to the input stage from the output stage, post-mixing.  The P45, however, uses passive mixing at the output, which puts the kybosh on that plan.

[zombiwoof]

Thanks Mark, I didn't know that!.  So, the original MXR Phase 45 pedals didn't undergo any of the the circuit changes the Phase 90 did during the pedal's lifetime?

You can't really have a feedback path with a 2-stage phaser like the P45.  To avoid signal-phase issues, the feedback path needs to be an odd number of stages.  And in the case of a 2-stager, that means the 2nd stage would send its feedback to itself.

That said, some FX that use feedback send it to the input stage from the output stage, post-mixing.  The P45, however, uses passive mixing at the output, which puts the kybosh on that plan.

[Mark Hammer]

There were essentially two changes that the P90 went through: variations in the amount of feedback/resonance/emphasis, and variations in the sweep width.  Three knob phasers will have these as variable controls, where MXR stuck with one knob (Rate) and fixed the other variables.

The P45 may have had different amounts of sweep width in various issues (I don't know this, but it is within the realm of possibility, and wouldn't surprise me), but that's it.  The 3M9 resistor on the LFO output sets the sweep width.  On some P90 issues, you will see it as 3M3, yielding a wider sweep.

Typically, one prefers a wider sweep for slower speeds, and a narrower sweep for faster phasing.  Slow sweep also sounds more dramatic with more resonance.  So the prototypic slow sweep would be wide and very resonant, where a fast sweep would have low or no resonance, and narrow sweep.  The various P90 issues are neither better nor worse, just better suited to faster or slower sweeps.  The P45 is really optimized for medium-fast to fast sweeps.