Modifying MFOS Phaser to bypass internal LFO

EDIT: The mod I’m discussing might already be a feature of the module as-is. I can’t quite tell if the external CV inputs affect the rate of the internal LFO or if they directly control the phasing effect. I might delete this post if it turns out to be utter bone-headery.

Hi all,
I’ in the process of building two Music from Outer Space phaser modules:
and I plan to link them into a stereo effect. I’m sure it’ll sound sick for both internal LFOs to be running slightly out of phase with each other, but I’d like to be able to bypass the internal LFOs with an external control voltage, to make the phasing modulation controllably by different wave shapes, envelopes, S&H, etc. I’ve never really heard a phaser modulated that way and I think it would be sick as heck. I’m trying to examine the schematic to identify where to inject the external control voltage, can any of you lend some insight?

From what I can tell, I think I need to take the collector of Q2 and run it to a switch so that the connection can be broken and replaced by the external CV. Does that seem right? Should I add any other active circuitry before the incoming CV signal, or do y’all think it can just go straight in? Here’s the schematic:

Thanks for any insight you can lend! I plan on adding a dual buffered attenuverter ahead of the external CV in, which I think will make for a very unique stereo effect.

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Looks like the phase shift control comes from U3-A and it’s configured as an inverting summing amplifier with some fixed offset (R11). One node comes from the LFO circuit via R12, but then there are R18 and R21 marked with CV1/CV2. This is where I would start looking to apply external control voltages. Turn the DEPTH on the LFO all the way down, and apply voltages on either R18 or R21 and see what happens.


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Set the potentiometer R10 Depth to 0 and then an ADSR or whatever in CV1 or CV2 or both a voltage and you have what you wanted.
Have fun tangram

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Thanks guys, I think you are right and there is no need for a mod. I might delete this and just post my results when the project is done.


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I finally finished with this build and yes, the CV inputs directly control the modulation of the effect, rather than the rate of the internal LFO. I’ll post results when I have the chance. I would delete this thread because of my dumb question but I’m not sure how.

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