More on Crosspoints.

[Grant Richter]

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.

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.

----------
>From: Tony Clark <clark at andrews.edu>
>To: Synth-DIY <synth-diy at node12b53.a2000.nl>
>Subject: Re: More on Crosspoints.
>Date: Thu, Jun 15, 2000, 2:01 PM
>

>    More thoughts on the subject,
>
>    The MAX335 looks like an excellent chip for your application, Paul!
>
>    More thoughts on the subject, regarding Crosspoint chips...
>
>    Having looked at the Mitel chip MT8816, I noticed that you can
> literally control each switch.  Well, wouldn't it work that if you tie
> the output lines directly to an opamp's in I/V configuration and then put
> the input resistor on the input line of the crosspoint...would that work
> then?  You wouldn't get any additional feedback from one channel to the
> next because the inputs are now protected.  The output is your summing
> node of your op-amp which should now handle the multiple signals being
> fed by the multiple switch-points.
>    I suppose the issue then is if the crosspoint is feeding current, if
> so, then perhaps this would be a single chip solution!
>    Feedback?  I'm probably way off.  :)
>
>    Tony
>
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