More on Crosspoints.

[Tony Clark]

> The problem is you are now connecting two summing nodes
> together and the servo action will cause them to "fight" each other.
> This could cause oscillation or DC problems.

   Well they aren't literally tied together.  There is separation of the 
two summing nodes by two switches.  The combined on resistance of the two 
should at least prevent some servo action.  In this situation I'd feed 
the signal directly into the crosspoint input and that should tie one end 
of each switch and the other end would be the summing nodes.  I'd try to 
find a crosspoint switch with as large an ON resistance as possible to 
set the input impedance level as high as possible. 
   I guess I should try this with some FETs and see what happens.  :)

> One solution would be to time multiplex each of the eight outputs
> using the crosspoint switches as the input to a hold capacitor.
> You sampling aperture would have to be one eighth of 44.1 Khz
> and each input would need a 20Khz anti-aliasing filter.
> 
> This should eliminate interactions because no two outputs are
> connected together at the same time. By pulse width modulating the
> switch duty cycles, it would be possible to make the switch array
> behave like an array of variable resistors. So the relative amounts
> of "mixing" from each of the eight inputs to each output could be
> controlled in the crosspoint array itself.

   Sounds complicated.  :)  At that point I doubt there will really have 
been any PCB real estate saved by utilizing the crosspoint chip and it'd 
be better to just wire a bunch of those MAX355 chips together.  :/
   Would love to hear more ideas/knowledge!

   Tony

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I can't drive (my Moog) 55!         |     The E-Music DIY Archive
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Tony Clark -- clark at andrews.edu     | aupe.phys.andrews.edu/diy_archive
http://aupe.phys.andrews.edu/~clark |     Contributions welcomed!
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