[sdiy] Practical Elecronics "Minisonic2"

[Julian Bunn]

Thanks to everyone for the warm welcome.

The problem with the triggering is as follows: the circuit has to
detect when one of the keys is pressed, but without loading the
resistor ladder. This was originally done by injecting an HF signal
onto the ladder, and then capacatively coupling an HF detector to
the ladder to detect when a key was pressed. Apparently this didn't 
work very well. The upgrade was to use the double pole Kimber Allen
keyswitches, which made the job of detecting a keypress separately easier!

But since I don't have those, I need to have another method. Doug Shaw
suggested I DC attach a FET opamp to the keyswitch bus, taking advantage
of the very high impedance in a follower configuration, and so I've
been fiddling around with a TL071 that does that. It seems to work
nicely (there is no bus loading), but my problem is connverting the 
0 to -2V voltage swing at its output to the 0 to -9V voltage swing I 
need as a trigger to the Envelope Shapers.


Julian

> -----Original Message-----
> From: john mahoney [mailto:jmahoney at gate.net] 
> Sent: Friday, April 30, 2004 12:54 PM
> To: synth-diy at dropmix.xs4all.nl
> Cc: julian at cacr.caltech.edu
> Subject: Re: [sdiy] Practical Elecronics "Minisonic2"
> 
> Indeed, welcome, Julian!
> 
> 
> > .... I'm actually struggling with a FET opamp
> > interface to the keyswitch bus which I need to trigger the envelope
> > shapers. I'm not an an electronics engineer, so this is proving a
> > bit tricky!
> 
> You've come to the right place. There are duffers here (like 
> myself) but
> also plenty of real experts who are quite generous with their 
> knowledge.
> 
> 
> > I will also be adding all the circuit diagrams to the site, once I
> > get permission from the original author, who I am in contact with.
> 
> Great! Always fun to see different circuits.
> 
> 
> > Thanks ... I think I was fortunate with the keyboard. It turned
> > out to be exactly what I needed, ...
> 
> Please tell us what make & model that was, thanks.
> 
> 
> > I was surprised I couldn't find anywhere on the Web which sold
> > bare keyboard assemblies. There must be such places, of course.
> 
> Nah, resistor ladder keyboards are unfortunately "obsolete." 
> Now they all
> have matrix switches, with 2 switches per key for velocity 
> sensing, IIRC. *
> 
> Have fun!
> --
> john
> 
> 
> * IIRC = If I Recall Correctly, a common acronym on this 
> list. The older we
> get, the more we tend to say that. ;-)
>