MXR Phase 45 Conversion

[Jdansti]

Crontox102098 has requested that I help him start a thread about using an oscillator with an LED/LDR on an MXR Phase 45.  He is in Columbia and there's a bit of a language barrier (not that I know much Spanish, but I am fluent in GoogleTranslate ).

I know nothing about how to do this or even how the Phase 45 works, so I hope that some of the experts can help him out.   I've requested that he follow this thread and answer questions that you forumites pose.

Here's his question to me:

"I have a Phase 45 medium build and lacks [sic-has? JD] the FET, I wonder if I can replace that with some kind of FET oscillator containing an LED that illuminates a LDR and create the effect, undrstand??

I do not throw it away ..."

Any help would be appreciated.

Thanks-JD

[amptramp]

A few answers here:

The FET's on the Phase 45 are used as variable resistors which permit variations in phase by changing the time constant of a capacitor and the variable resistance of the FET.  They can be replaced by LDR's with a light source connected to the LFO (low frequency oscillator).  The LFO itself does not use FET's.  In the original circuit, the LFO drives the FET gate pins to vary the resistance.  I believe there may be a circuit that already exists to convert the FET variable resistors to LDR variable resistors, but you should know that LDR's are even more variable in device parameters than FET's, so you may have to select and match them yourself.

This thread:

http://www.diystompboxes.com/smfforum/index.php?topic=99862.0

may give you some answers.

[Jdansti]

Thanks for the information, Ron.   Even though this is crontox's topic, I'm learning from this too.

[amptramp]

A more complete explanation is here:

http://www.geofex.com/

In the upper left of the geofex page, click on "the technology of" and it will take you to a page with some choices.  Select "The technology of phasers and flangers" and you will get a good description of how it all works.  Once you know that, then you will know what you need to do.

[Jdansti]

Thanks.  I just read it and it's an excellent article!