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WIGGLING 'LITE' IN GUEST MODE

filter mod?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author filter mod?
Kwote
was playin around with the dual filter as a clock and i found it to be pretty sporadic.

this is due to it not having a low enough frequency range. is there a mod you can do to extend the freq's range as low as the VCO?
Muff Wiggler
maybe there is, but my gut feeling on this is 'no'

my understanding is that while an oscillator is designed to oscillate, a filter is not. a filter can be 'coaxed' into oscillating by feeding back a portion of it's output back into the input, and maintaing a high frequency - the frequency becomes the rate of oscillation

however you slow the oscillation down by lowering the filter's cutoff frequency. if you lower it too much, it simply is no longer high enough to tickle the filter in an oscillation, even with high feedback levels. because the filter is not designed to naturally oscillate all the time.

now something like the Mankato IS designed to maintain oscillation even at very low rates, which is one of the very cool things about it

so, you need a filter designed for this - or a vco - or use the filter as a clock at higher rates only

just my gut feeling anyway, could be wrong
Kwote
Muff Wiggler wrote:
maybe there is, but my gut feeling on this is 'no'

my understanding is that while an oscillator is designed to oscillate, a filter is not. a filter can be 'coaxed' into oscillating by feeding back a portion of it's output back into the input, and maintaing a high frequency - the frequency becomes the rate of oscillation

however you slow the oscillation down by lowering the filter's cutoff frequency. if you lower it too much, it simply is no longer high enough to tickle the filter in an oscillation, even with high feedback levels. because the filter is not designed to naturally oscillate all the time.

now something like the Mankato IS designed to maintain oscillation even at very low rates, which is one of the very cool things about it

so, you need a filter designed for this - or a vco - or use the filter as a clock at higher rates only

just my gut feeling anyway, could be wrong


it's all good if not. i don't mind the sporadicness. just lookin for extra flexibility. thought maybe a pot with a higher value might work?? but i also thought a filter designed with this application in mind would be my main option.
Kwote
yo lol

your post gave me an idea. i put the filter in extreme Q, then literally fed back the signal via the mult. presto! attenuating the mult gets me mid to super fast clocking abilities.

YAY!!!!!!

grin

not as slow as i'd like but damn better than before.

edit- i messed with it a bit more. there was a bit of drop out and it got sensitive here and there.

i tried the same patch with the filthy and it didn't work. something about the dual that makes it work. adjusting levels on both A & B. pretty weird but cool nonetheless.
consumed
speaking of a filter mod...is it possible to mod the dual filter to take a CV at the frequency control?

EDIT: talked with john blacet on this--the module is really not designed for CV of frequency.
Kwote
consumed wrote:
speaking of a filter mod...is it possible to mod the dual filter to take a CV at the frequency control?

EDIT: talked with john blacet on this--the module is really not designed for CV of frequency.


yeah. the truth is i'm kinda glad it doesn't. maybe right now with my system as small as it is it would be nice. but i know once i expand further i'm gonna be happier with the simplicity.

all in all i'm pretty juiced with this addition to my setup.

that clock patch was fun. lot of random adjustments on the levels of A & B to get it just right.
Muff Wiggler
i think it would be a prime candidate for the hacked quasi-cv via vactrol

on the downside, CV control is not scaled using the approach. and you cannot deal with negative voltages at all

on the plus side, it's a very very easy modification, only needs two parts, nothing touching the PCB, and easily reversed if it doesn't do anything for you

you can do this 'trick' on ANYTHING with a pot. Guitar pedals, modules, etc etc. Just know it's not precise, it's not scaled, it can't take AC signals, etc. But it is cheap and easy and pulls a bit of extra voltage control out of your module
Muff Wiggler
btw, GREAT idea with the attenuator and feeback Kwote. You're really thinking in a modular way 8)

as you've probably realized, filter "Q" (or 'quality' or 'peakiness' or 'regeneration' or 'resonance' as the terms are all freely exchanged) is simply the feeding back of some of the output signal back into the input.

On filters that don't have a resonance adjustment (are there any? perhaps an eq.....) you can fake it by splitting the output, and mixing some of it back into the input.

On filters that don't have voltage-controlled resonance, you can add voltage control by putting a VCA in the path of this splitter/feedback path and using that to have CV control of how much output gets fed back into the input, giving you VC'd resonance.

This is one of the reasons you often see multiple inputs on filters (like the Mankato - which doesn't have VC'd resonance), so that you can patch up VC resonance on your own and have an input jack to feed it back in.
Kwote
werd. there you go.. making me run out of VCA's for cool shit again.

i gotta get a new SKB badly! lol
consumed
Muff Wiggler wrote:
i think it would be a prime candidate for the hacked quasi-cv via vactrol

on the downside, CV control is not scaled using the approach. and you cannot deal with negative voltages at all


not a problem! dont care about scaling, just want some kind of control over frequency is all. when you say "cant deal with AC" does that mean that negative voltages are just ignored? thats fine, i can deal with it. where can i find out more about the mod?
Muff Wiggler
yep, negative voltages would be ignored. It's a 0v-and-up sort of thing

also vactrols are slower than voltage is (which is why they give that nice musical 'slew' when used in filters), so if you were feeding it fast AC, i'm not sure what you would get. it would only respond to stuff above zero (going up and down), and it would respond slower than the voltage rate, so if you had a fast enough signal you would probably overload it and it would simply register full-voltage all the time.

Not sure where you can get more info, I know a few people who have performed this mod on both modules and guitar pedals, but for some strange reason THEY REFUSE TO TALK ABOUT IT OR ANSWER ANY QUESTIONS which is really wierd AND frustrating.... but anyway my understanding is that it is very simple -

a vactrol is simply an LED and a LDR (light dependant resistor) that are pointing at each other and sealed together in a lightproof casing. Also known as an 'optocoupler'. You can make your own by putting together an LED and an LDR inside a ball of black putty.

anyway....

You'll have four leads coming out of the vactrol, two on the LED side and two on the LDR side.

You want to install a jack, and wire the tip lug of the jack to the input wire of the LED. I suspect you want to attach the other LED wire to ground, but I've never done this myself, so I'm not 100% sure here, but there's not a lot of variables in this setup so a little experimentation should get you there pretty quickly.

Now with only this setup so far, you can easily imagine how when you present a voltage to the jack, it will power and light up the LED.

Next, we have the LDR side of the vactrol. Again, two wires. Connect one to the input lug of the pot you are trying to add CV control to. Connect the other to the output lug of the same pot.

Now, a pot is a variable resistor that has a value set by the amount that you turn the pot. The LDR is a variable resistor as well, and you have placed it across the pot. When the LDR is not getting any light, your pot should act as it normally does. When it IS getting some light, it will act as if the pot has been turned, by changing the resistance across the pot.

that's the theory behind the deal, and a basic explanation of the wiring. Again i've never done it so you may need to experiment a bit with the wires, but that's everything you should need to know to get there.

Someone should do this and then come back and fine-tune these instructions based on real-world experience. Pics would be a huge plus 8)
Muff Wiggler
Here's a nice video where Cynthia gives a handy little info session on vactrols... thanks Cynthia!

consumed
thanks muff. the VTL5C3 is probably the one to use. it looks like there are different little circuits out there in DIY land to work best with their intended targets. ill have to play around with it.

EDIT: correction-probably a VTL5C3/2 instead.
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