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Hi, gang! Here are some gut shots of my Memphis Tremolo modulator, and also an x-ray component side shot of the PCB showing parts & placement. I have seen gut shots of many other Memphis pedals online that use the exact same PCB! VERY clever engineering! I had originally intended to draw up a schematic also, but I'm too lazy to do that by hand anymore. Perhaps a group member might suggest an intuitive (like: drag and drop schematic symbols from a list) program for drawing schematics?

Hi!
First of all, the work you did and the resulting drawing (i find it aesthetically pleasing as well as useful).
I've worked out the "2sK641" in your drawing to be in fact a "2sA641". The "SK" is a mosfet, the "SA" is a pnp bjt transistor.
I'm not sure what the other transistor is though but i can't find anything about a 2n171. It says "K92 N171A" on it so it could be a japanese "2SK92-N1" which is a jfet :
https://www.datasheetarchive.com/pdf/do ... term=2SK92
I was also wondering how it's powered. Is it the bog standard 9v?

I got curious and took the liberty of drawing a schematic, hopefully not preventing you from trying out drawing software. In fact you should probably draw it up yourself because mine could contain mistakes and i'm not really satisfied with how i drew some bits (i made a weird job of the vb voltage divider), it's a bit of a rush job for now, but there you go. I might revisit it, time permitting.

I used Kicad 7's schematic editor to draw it by the way. It's latest version but i'm still on the fence on whether i like it better than the previous one. It does some things that i hate, like moving my cursor for me.
There are lots of tools and features that i would never use but it's pretty intuitive once you find what you actually need.
A very bare bones, dead simple schematic editor you could also try is BSch3V
I'm sure people will suggest other options for you to try.

Thanks for your pictures and tracing!

Any checking and correcting is more than welcome.

Krystal, thanks for your excellent work. It was 2SA641 on my drawing, but my handwriting is not always sufficiently legible (another reason why I should draw schematics with a computer). Yes, the battery is a standard 9v. I too was a bit puzzled by the 2N171. Have you ran your schematic through any sort of pSpice program, or are you very certain about the 2SK92?

This looks like they took the phaser and modified it to do tremolo. The diode is a 5.6v zener I think. It's a 2SK92-N1 for sure.

Thanks guys !
I've updated the schematic. You're right CheapPedalCollector, it's a 5.6v zener indeed.
I can't find a demo of this thing, I guess i'll just have to breadboard it.
It does look like a single stage phaser because the phase oscillator is done with an opamp rather than tube or transistor with a cap and resistor network, but it might still be a 360° phase shift oscillator. You would have to be smart and know how to do the math and simulations to find out. I'm just a donkey brained individual what doesn't know how to use the simulation side of the software. I should look into it someday.

Well I mean, they literally repurposed the Memphis Phaser board. It's a Phase 90 clone, I noticed that the oscillator is pretty much the same.

Sorry I missed the Zener. Memphis also used the same PCB for their Mini Flange...

I forgot to ask! Does anyone know where I could buy a replacement bottom plate for the enclosure?

Notice that it's very close to a one stage MXR Phase 90.

Minor schematic fix:

What would be the best way to have the lfo inverted in order to try a stereo version? Or would this be possible? Thank you

The oscillator is called a 'relaxation' oscillator I believe.

You can easily invert it's output by adding an inverting op-amp stage after it. Could use 2 dual op-amps then.

I'd personally replace the output transistor with an op-amp summing amp as it's be a nicer and higher headroom way to do it than what's done here.

Thank you, output would be in the crossing between R10 and R15?

Yes