"chopper" footrocker pedal idea (crazy)

[Paul Perry (Frostwave)]

Logically follows from the 'stutter' thread, but putting here because drifting threads get lost wiht this format.
Anyway, imagine an optical wah, the kind where a shutter cuts off the light to a LDR gradually. Now use a shutter that is striped! so you can have a rocker with adjustable speed as you 'rock'. Very low parts count.. and I personally think that a LDR WILL be fast enuff (Sorry Mark!) but, only xperimwnt will tell. Go for it!

[sfr]

...

[Paul Perry (Frostwave)]

I was thining, anyone with an 'optical' foot controlled volume, like a George Dennis or Morley, would find it VERY easy to temporarily mod it to a "stutter shutter".

[Nasse]

Correct me if I am wrong but I remember old G Anderton book (Electronic projects for musicians or something) there was a noise gate project using led/ldr combination, of course it was CLM6000 or thereabouts, which may be a fast attack/decay component. In the demo audio record there was an example where the gate was driven by some keyboards auto-accompaniment or rhytm envelope, so it is proven that led/ldr can be fast enough. I think some good noise gate circuit may do what is under discussion.

Idea about stripes is wild, but maybe average wah or vol pedal movement is somewhat small so count of stripes is limited. How about a cylinder with stripes at its edge, and just kick it for more rpm or step on it to slow speed.

[drew]

Hi Paul...

Actually, the Optigan, a consumer-market organ from the 70s made by Mattel, used this principle in its volume pedal. The Optigan was a ramshackle quasi-Rube Goldberg instrument in that it achieved everything it could through mechanical means... unfortunately, it means that its tuning and operation were unstable and susceptible to partial or complete failure!

That was just a tangent, I've owned one before and it was a nightmare. In the case of the Optigan, it used a similar striped piece of celluloid film, with the area of the light behind it big enough to cover several stripes. I think it was done this way because lower-resolution line art was cheaper to print on this tiny 1"x4" piece of film than halftones.

At the top of the pedal's travel, the film was completely dark, and had small stripes of transparence growing bigger as the pedal moved downward to completely transparent at the other end.

It should be noted that the tone generator in the Optigan was fashioned from rotating rings in a similar celluloid disc with 56 (or thereabouts) individual photocells picking up amplitude-modulated signals from a long lightbulb shining through the disc.

Did I mention that the lightbulb was irreplaceable and that any foreign matter inside the organ or in the environment could get sucked into the works and block the photocells or bulb?!


drew
toothpastefordinner.com

[phat-ass]

Check this out

http://www.wfmu.org/upcoming/www.amphilsoc.org

Strange coincidence...

phat

[Mark Hammer]

Paul,

No apology needed.  An LDR probably *could* do the stutter thing.  You'd just have to be very careful about which one you use and how much of its range you want to use to accomplish the effect, and that's tricky to do.  Not impossible, just tricky.

Part of the speed thing is how long it takes to go from max to min resistance and back again.  Conceptually (and on paper) the amount of "travel time" is also a function of the amount of travel.  Spec sheets for LDR and optoisolators usually show a response curve that looks slightly curvilinear such that amount of resistance change per unit of time is faster in some parts of the resistance range than others.  I suspect that if you cascaded several LDR-based "shutters", such that each one only had to "move" a bit in resistance, and was responsible for several db of attenuation/gating but not ALL of it, you could get some pretty fast onset/offset specs.  Expecting a single LDR to do all the attenuation needed for a robust chopper, though, might be expecting way too much from it.

Or am I foolishly pursuing specs and assuming the human ear can tell the difference between a *marginally* trapezoidal amplitude change and a true square one?

[Paul Perry (Frostwave)]

Embarassingly enough, I used to have a couple of Optigans!! (but, never looked inside the pedal!). My kind of technology, I gotta say... nothin like putting dics in upside down so the banjo 'sucked' instead of 'plucked'!
As for opto shutter technology, using a small solar cell as picup, you get a VERY fast response chopping a modulated light beam (just did this for the Australian Braodcasting Commission, building the electronics for a reconstruction of a Percy Grainger 'free music' device. Tried a LDR but of course as Mark H says, too slo..).