[sdiy] Aftertouch via Pressure

[ChristianH]

What about using the rubber hose instead of the felt strip below the
keys, so that the assembly weight won't come into play?

However, this would require a quite thin hose, and thus smaller pressure
changes. Furthermore, the keys usually touch the felt strip on a small
area (almost like a knife), so the poor hose would be squeezed quite a
bit. Might not be very durable.

Christian



On Wed,  9 Jul 2003 15:53:05 +0200 jhaible wrote:

> This is what I meant: "the mechanical part is difficult." 
> 8-)
> 
> I think PPG Wave synths had an aftertouch like this.
> 
> I expect it would be hard to get such a stucture _sensitive_.
> The weight of the whole keyboard action must not cause an
> Aftertouch output, but the additional pressure from the fingers
> has to ...
> 
> JH.
> 
> 
> Zitat von Glen <mclilith at charter.net>:
> 
> > At 05:39 AM 7/9/03 , jhaible at debitel.net wrote:
> > 
> > >But the mechanical part is difficult. You must find a way to insert
> > >the tube (hose?) beneath the keys, such that it's equally actuated from
> > >blacks's and white's. And, worst of all, you have to find a way to
> > >get enough key travel even with the additional thickness of the
> > >tube. But then again, the SH-2000's keyboard also has reduced 
> > >key travel, and it plays nicely ...
> > 
> > Mount the back edge of your keyboard assembly on a hinge, possibly piano
> > hinge (that eliminates any alignment problems of multiple small hinges.)
> > Place the front edge of your keyboard assembly over the sensor hose (which
> > would run from left to right, underneath the whole keyboard.) The front
> > edge would need some springs added to help hold the keyboard assembly down,
> > just in case your instrument was ever turned upside down--possibly when
> > being transported. You might even add some "return" springs underneath the
> > front edge of the keyboard to ensure that the keyboard would move back up
> > to its proper resting position after you stop pressing down on it. The
> > rubber hose underneath the front edge will provide a spring effect of its
> > own, but this will probably need to be augmented with such actual springs.
> > Using return springs also allows you to use a more flexible and more
> > sensitive type of tubing underneath the keyboard assembly. This should give
> > you a more sensitive assembly that needn't be pressed so hard that you
> > think you are going to break something, just to get some after touch. (My
> > Kawai K4 has after touch, but is far too stiff and insensitive for my
> > taste. I feel like I'm going to break something just trying to activate the
> > after touch.) If you mount your whole keyboard on a hinged sheet of stiff
> > metal (sort of a sub-chassis), you could even move the tubing away from the
> > front edge of the keyboard. This would allow for adding more pressure to
> > the hose, for a given amount of applied downward pressure, at the expense
> > of having to press the keyboard farther, due to leverage effects. (I hope
> > you know what I mean by this.)
> > 
> > All of this assumes that you only want to develop a global pressure
> > parameter, and not have individual after touch sensors underneath each key.
> > If that's what you really want, it's going to get a lot more complicated.
> > 
> > I look forward to hearing from other Synth-DIY members, as I haven't
> > actually seen a keyboard built like I'm describing, but I think it should
> > work. Let me know what you think. The advantage of my technique is that it
> > does not screw around with your keyboard's key action--just the keyboard
> > assembly mounting. The keyboard's keys should play with the same "feel"
> > that they always have.
> > 
> > 
> > later,
> > Glen Berry