[sdiy] Keyboard Schematics

[Gene Stopp]

If the keyboard has dual busses, you could make a simple current source from
an op-amp and transistor driving a resistor chain of 100 ohm 1% resistors.
The bus for these contacts would simply go to a holding cap and hi-impedance
voltage follower to provide the CV out. The other bus could have the
contacts all going to the +5 supply and the bus being the gate output (thru
a 1K resistor of course).

I have an old PAIA 3-octave Pratt/Read dual bus that I did this to, and it's
still laying around in the old PAIA Tolex case. It's my "test setup"
keyboard, and was never meant to be very accurate. But it's just fine! I'm
totally impressed with how good it behaves as a controller considering the
minimal effort I put into it. I think what happened is I used a nice
high-quality non-polarized polystyrene (or poly-somthing, don't remember)
cap for the holding cap, and a FET op-amp for the voltage follower, and I
kept the wire to the CV bus short. The droop over time is totally
acceptable.


Best Regards,

- Gene


-----Original Message-----
From: Lewis Bupp [mailto:lbuppii at hotmail.com]
Sent: Thursday, April 04, 2002 6:22 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Keyboard Schematics


HI Guys- After trying to resurrect a very old and very badly damaged Paia 
8782A and DAC, I have all but given up on it.

Now I have this old Paia kbd now that I do not want to throw away. I would 
like to use it to build just a very simple controller for my modular. CV, 
gate, Sample/Hold, etc. I really dont want to use the old Paia system of the

multiple trimmer pots. Anyone have any schemo's and/or ideas. ( I can hear 
the comments now.... THROW IT AWAY!) LOL.

Seroiusly, just something simple.

Thanks in advance.

Lew

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