Casio SK - velocity sensitive keys possible?

[gmeredith]

Hey everyone,

I just thought of an interesting idea. Since the SK samplers operate their voice ADSR envelopes using a simple CV line for each voice from the processor, and the maximum voltage of that CV signal determines the volume of the VCA, it would theoretically be possible to attenuate or boost that CV maximum voltage "on the fly".

I was thinking of how it might be done, by imagining some kind of velocity or pressure resistance switch added to the keys that basically put a variable resistance in series with each CV line. And so if you strike a key slowly, it throws a higher resistance in the CV line, and so a quieter note is played. Hit it harder, and the resistance is lower, and the louder the note. Actually, if a pressure switch was used, it would create aftertouch. This actually seems easier to do than velocity (I'm thinking of cheap, easily bought available parts here) as pressure conductive rubber sheeting is readily available.

Has anyone got some thoughts on this? it would be pretty strange to have an SK with a velocity or aftertouch keyboard 

Cheers, Graham

[Circuitbenders]

The theory is sound but the question remains, why would you want to?

I think that might fall under the catagory of 'over engineering' 

[gmeredith]

It feeds my obsessive compulsive behaviour in making my SK8 have every feature and gadget imaginable hehe

Cheers, Graham

[computer at sea]

Some of those repetitive sputtery glitches would sound fantastic with some increased control, particularly the stuff that comes off the 'skew' point on the far right of the board.

[gmeredith]

Well, you know, the more I think about it, there are stacks of simple things that can be done along the lines of what I've mentioned.

Using the pressure sensitive resistance rubber, you can easly replace a pot that may be in your bend points, so that pressing the rubber strip causes the bend to activate pregressively like aftertouch. You can even glue a button on top of the strip directly to make a convenient function button!

Cheers, graham

[Gordonjcp]

That's actually how the aftertouch in a lot of synths works.  In the Roland JX-8P for example, there is a strip under the keys at the front of the keybed.  This has (from the bottom up) a piece of circuit board with two "tram lines" along it (imagine two strips of veroboard, without the holes), a strip of conductive rubber, and then a strip of metal foil.  The whole thing is sealed over with plastic tape to keep it clean and dry and keep it together.  Google for "JX-8P aftertouch repair" or some such combination for diagrams and advice.

Velocity sensitivity is a bit more complicated, and relies on timing how long it takes for the key to go from "up" to "down".

[PolyPhuckin]

While having a search through Maplin the other day, i came across these weird little things, Quantum Tunnels.
They look perfect for creating aftertouch pads.

http://www.maplin.co.uk/module.aspx?ModuleNo=44202&doy=27m8

[gmeredith]

Actually, they are exactly the perfect thing for it. And at about $3 each, the price is right, too!!

Cheers, Graham

[PolyPhuckin]

this would be an awesome mod if it can be pulled off 
What would you attach them to? filter cutoff would be good.

Would love to see the results.

[gmeredith]

Well, I initially had imagined them being attached to the SK internal envelope CV lines, to control the velocity/aftertouch, but the world is your oyster now hehe!! Any bend point that was previously controlled by a pot or resistor will respond with this, in the same way the photoresistor "theremin" mods are done. The filter cutoff on my Phat Philter Bank mod could be controlled with it also.

Cheers, Graham