cross-point switches (was : PolyModular)

[David Halliday (Volt Computer)]

Just an idea - could you toggle the crosspoint switches on and off at a
couple hundred KHz?  Use a variable pulse width and..  well...  you get the
idea.



-----Original Message-----
From: The Dark force of dance [mailto:batzman at all-electric.com]
Sent: Thursday, May 06, 1999 6:34 AM
To: jbv; Edward Leckie; synth-diy at mailhost.bpa.nl
Subject: Re: cross-point switches (was : PolyModular)


Y-ellow y'all.
	Just a little point of interested I saw recently regarding x-points.

In a great many applications, X-point switches can't be used. For the same
reason some pin-board matrixs can't be used. This is because on synths such
as the VCS3, the pins themselves have a resistor in them. This acts like a
summing resistor into the summing node of an op-amp. Without this you cross
connect or just plain short out connections. Virtual shorting would occur
for example, if you x-point was set up to select inputs to an array of
virtual earth mixers. Where the summing node is at "virtual earth"
potential.

However, although the part number escapes me for the moment, MAXIM have a
new range of x-points which have a guaranteed 1500 ohm on-resistance. As
long as 1500 ohms would suit your purpose, or you could taylor your system
to require 1500 ohms, this would act exactly like the pin-matrix on a VCS3. 

They also boast the usual negligible spill and bleed-through and all that
stuff.  So perhaps these might be worth a look at for that purpose. I think
they do 8X8 and 16X8 if memory serves.

Hope this helps.

Be absolutely Icebox.

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