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Mr Multi question. LFO and modulation experts needed.

Started by bsoncini, February 08, 2018, 07:45:57 PM

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bsoncini

So I've been playing around with the mr multi effect from deadendfx.  It is a pedal in a wah type shell that can do phaser, wah and phaser/wah.  There are two modes, pedal (like a normal wah rocker changes a wah) and auto (the rocker changes the speed of the lfo)  https://drive.google.com/file/d/1QbppBPfFKRl6m2rRbaT0r3LOu_Ug9XWB/view.  I'm a bit lost in the schematic with all the switching and need your help.

I've gotten this to work with many different jfets that I have matched (2n5952, 2n5485, BF245c, J211) which sometimes requires changing the zener diode and rebiasing.  I get the phaser to work pretty good with all of them.  But when I switch to the wah, phase/wah mode it is really trebly.  Obviously this is only a problem in lfo mode because in the other mode I changed the sweep with the rocker.  The wah mode also has a bit of a volume drop, phaser/wah also a bit of volume drop but less.  Any idea of things to try, parts to substitute, or maybe something I messed up? 

How do I make the lfo peak to peak voltage bigger, what parts should I change?  In lfo mode I would like to get as deep a phase as possible.  In manual mode the resistance between the drain and sources goes from 39k to about 250 ohms.  And it works great.  In lfo mode it swings between about 450 ohms and 2.2k obviously this changes a bit due to biasing. Maybe the orignal jfets (2sk30a-gr) have a much better or quicker sweep in the ohmic region?  The lfo swings about 960mv.  In pedal mode I get the voltage changing about 1.8 volts from heel down to toe down.

Is there a way to add a depth pot for the fast lfo speeds?  This pedal has a pot labeled depth but it just turn the lfo from a triangle wave of 960 mv peak to peak to a 2.25v swing with a sort of saw tooth wave? (real slow rise, then a sharp drop) and slows down the lfo speed in the process.  The phasing is nice and deep when playing with the depth knob but the wave form gives it a real wonky sound which can be cool in certain moments.

Which leads to my last question.  What parts would I changed to play around with the lfo speed?

I've built many phasers before but never really tweeked them much.  I've had fun with this one learning about jfets as variable resistors but my lfo skills are lacking.  Well, there is enough info on the web about lfo's and tweaking phasers, but I'm a bit lost with all the switches on the schematic and what exactly is happening in wah and phaser/wah modes. I've tried to figure all this stuff on my own by reading (getting lost in too much info), switching parts, etc and I've hit my limit on what I can do on my own.

Thanks in advance for any advice.