The Waschillator - LFO + op amp wah

[culturejam]

You're cool with people building these up, culturejam?

Of course! If I wanted to keep something a secret, I wouldn't post it on the internet.

I should warn you, though, that it sounds awesome on clean. But the filtering is wonky for dirt. It's hard to describe. I never got around to monkeying with the wah cap values, so it may be just as simple as that. I didn't do any sort of math or analysis yet, so that's just a guess.

[tabbycat]

It's theoretically similar to the OptoChopto, being a wah with an LFO to vary the sweep. But it's implemented quite differently (different LFO, different wah). The Chopto's LFO is one I tried many years ago. Can't get that thing not to make a ton of noise (not the good kind). It clicks like mad.

Adding a square-wave (stutter) is trivial. But it's not going to be all that square because the optical element doesn't react linearly (it turns on faster than it turns off).

thanks for the reply and info culturejam.

have been thinking about modulation ideas and cobbling something together into a stuttery feedback looper. have been browsing 'the escobedo files' for freaky modulation starting points but am interested in using your adapted tremulus lfo as a 'block' (if you don't mind. just a one-off diy thing for me). i was going to use the schmitt lfo end of the optochopto but for the same reasons you gave, nocentelli warned me off it due to the ticking and recommended your stm lfo instead.

i read your comment in another thread here http://www.ilovefuzz.com/viewtopic.php?f=151&t=27516#p480365
"The LFO is also from the Lune, but I simplified it to just three controls. I also improved the electrical isolation between the audio and LFO so that there is ZERO LFO tick in the audio"

have compared your schematic above (waschillator) with this schemo of the stm http://img441.imageshack.us/img441/8429/stmschematic.png and as i understand it, the lfo bit is the section starting with the 220k pair voltage divider and ending with the leds, isn't it? and i put the ldr (or ldr side of a vactrol) across the poles of whatever i'm triggering with it?
am intending to use a LM741 or TL062 instead of the 4558. mark uses a TL062 as an alternative here http://1.bp.blogspot.com/-46FiaOG3V8o/UVqmCGXvVfI/AAAAAAAAFW4/iQxN6152tH0/s1600/Culturejam+-+Shoot+The+Moon+-+2+Knob.png which people seem happy with. am out of 4558.
haven't done anything with an lfo yet so apologies if this seems rudimentary beginners' stuff. i am one.

re the waschillator led/ldr/vactrol v opto ic comparison, the led/ldr sounds sweeter to me. seems to move more air around. but trades phase for wah feeling in the process.

[culturejam]

am interested in using your adapted tremulus lfo as a 'block' (if you don't mind. just a one-off diy thing for me).

As I said above, anything I've posted on the internet is fair game for whatever anyone wants to do with it. I didn't invent that LFO from scratch, I merely modified an existing design to meet my needs (and I feel like I improved the filtering a bit as well).

have compared your schematic above (waschillator) with this schemo of the stm http://img441.imageshack.us/img441/8429/stmschematic.png and as i understand it, the lfo bit is the section starting with the 220k pair voltage divider and ending with the leds, isn't it? and i put the ldr (or ldr side of a vactrol) across the poles of whatever i'm triggering with it?

Yes and yes.

am intending to use a LM741 or TL062 instead of the 4558.

LM741 will not work. It's a single op amp. You need two op amps for the LFO, so go with TL062, if that's what you have on hand. Pretty much any dual op amp will work, although there may be some differences in the waveforms (and there are a few that just don't seem to play nice with certain LFO circuits, but it's not very common).

[tabbycat]

^ hey culturejam, many thanks for clarifying the lfo bit, and the opamp. it does seem to get mentioned a lot as a good circuit block for lfo on various forums, so you must have done something very right with your refinements.

i'm ok for TL062 so will go with. can't remember how i arrived at LM741 (edit: was thinking of the TL072) but glad to know early on it's wrong. just moving from mostly transistor circuits to those using ics so get mixed up with the different combos. like the pinout thing on transistors, eventually i'll get a feel for it. all fumbling around until then.

am looking forward to seeing your next thing. are you in a modulation mood atm?