Voltage gate?

[spinoza]

Hi

I've been playing around for voltage controled oscillators, and I'm wondering, if there anything like a simple "voltage gate", i.e. a piece of circuit that will only let electricity pass if voltage is over than a certain limit?

I want to use this to prevent "click" noise from coming out of my osc when there's an interference coming from the voltage controler.

[gez]

Not really clear what you mean.  If you wish to gate an oscillator when a control voltage falls below a certain level, then that's doable.

The reset pin of a 7555 oscillator can be triggered by a comparator/Schmidt trigger to enable/disable it.  Similarly, a device from a 4093 NAND chip can be wired as a 'triangle' oscillator.  With one gate tied to logic high the oscillator works, when tied low it doesn't.  The 7555 can be wired as a Schmidt oscillator too and takes up less room, though with the 4093 you have the option of using the rest of the chip for other things.

It's possible to use logic chips in a similar way to replace/be a part of the Schmidt/square wave generator part of a triangle oscillator to enable/dissable it.  I've even used them in sine wave LFOs.  If your VCLFO uses a square for any part of the circuit, then it's pretty straightforward to do.

[spinoza]

It's the synthstick vclfo, which is a square wave based on the 40106 chip.

Sometimes when I move the stick a bit, there's interference and/or static electricity that seems to activate the lfo at frequencies so low that I hear only 2-3 small "clicks". What I want to do is to reject that voltage, ideally using the 40106 itself for it.

Is it doable?

[gez]

It's the synthstick vclfo, which is a square wave based on the 40106 chip.

Sometimes when I move the stick a bit, there's interference and/or static electricity that seems to activate the lfo at frequencies so low that I hear only 2-3 small "clicks". What I want to do is to reject that voltage, ideally using the 40106 itself for it.

Is it doable?

The 4093 chip can be wired up to do exactly what the 40106 chip is doing.  As each device has two gates, one can be used to enable/disable the oscillator. 

How to plumb this in?  I'd need to check over the schematic (don't have the time right now, but if I find some I'll get back to you). 

I'd say it's doable, but it's not something that just requires changing a cap here or there, you'll have to incorporate some additional circuitry/change layout.

[gez]

It's the synthstick vclfo, which is a square wave based on the 40106 chip.

Sometimes when I move the stick a bit, there's interference and/or static electricity that seems to activate the lfo at frequencies so low that I hear only 2-3 small "clicks". What I want to do is to reject that voltage, ideally using the 40106 itself for it.

OK, had a brief skim thru the article.  The oscillator isn't voltage controlled: the strip, when the conductors meet, completes the circuit for oscillation to begin and the length of strip determines resistance used in the oscillator, and therefore frequency.

The clicks are probably a result of misstriggering.  Don't know how easy it was/is to make this - I only skimmed thru the article - but perhaps widening the gap between the conductors (if this is possible) might cure the problem?

[spinoza]

It was indeed a problem with the strip. I re-did it entirely to add "fretboards" (I hid parts of the ribbon that were not in the chromatic scale with tape). And it does not click anymore.

Sucks that it's not a real VC as I wanted to use it to control my SH101 too. Well, too bad, I'll make the VC-equiped one next time.

[no one ever]

It was indeed a problem with the strip. I re-did it entirely to add "fretboards" (I hid parts of the ribbon that were not in the chromatic scale with tape). And it does not click anymore.

Sucks that it's not a real VC as I wanted to use it to control my SH101 too. Well, too bad, I'll make the VC-equiped one next time.

...cool. did you mathematically calculate the length of one 'fret' to another? isn't the ration like 1 to 12sqrt(2) or something like that?

[spinoza]

I tried to, but sadly the ribbon's resistance is not constant enough.

I'm tuning each and every note with a PODxt... pretty boring job!

[Quackzed]

id love to see the "fret job" your doing when it's finished.
i had the same idea i think.... to cover the conductive videotape with tape except where the frets would be... for a guitar synth that is "tuned" rather than "fretless"
... i had another idea you might like ... to use a slider as a volume pot... i was thinking of messing with the taper to try different feels of off to fade in of note... i also considered wiring both sides of a 1M pot to ground and having the loudest signal be at center of the slider so you could "strum" up and down
-----vvvv\/\/\/\/vvvv-------------vvvv\/\/\/\/vvvv------------vvvv\/\/\/\/vvvv------------vvvv\/\/\/\/vvvv---------

[spinoza]

The first thing I tried was to put a piece of mylar surrounded by rubber, and another mylar on top. Pressing that "sandwich" allowed the sound to pass through and mimicked "picking". But I find out that it's better when you can play with both hands holding the stick upwards, like a mini double-bass. It's less natural and "guitar-esque" to play by doing only taping, but it's fun.

I didn't fret (or tune) the higher notes, since they were too close together, and it's pretty fun to have a theremin-tannerin-like part on the same stick. I'll add a couple pictures when it's done.

The next one I build will have two "strings", with a little less range each, controling the same VCO. This one will probably have the "sandwich" implemented because it's for my girlfriend, who plays guitar (I play saxophone so 2 hand playing was OK with me!).