multiple power supplies in a modular

[Tony Clark]

> >One approach I've used (er - copied... :) is to have a standard
> >power supply of, say, +/-15V or 18V and the first thing on each
> >board is a pair of 100 ohm resistors and then 100uF caps to
> >ground. Works for me.
> 
> Well I don't do this. And in as sense I go one better. Every op-amp and
> every analogue IC and active circuit block is decoupled by a 50 to 100 ohm
> resistor (metal film) whith a capacitor across it. Usually an electro of
> about 1 - 10 mikes. Whatever it's not that important.

   Actually it is rather important what size cap you use as what you are 
making is an RC filter.  You want the cutoff to be something that's going 
to cut out most of the crap.  Utilizing a 100uF with 100 ohms gives a nice 
cutoff of 15 Hz, filtering out that 60Hz stuff even.  :)  But I don't 
like utilizing 100 ohms due to the drop in power supplied to the chips.  
I tend to use 22 ohms instead.  This gives a cutoff of ~70Hz or so which 
is adequate enough to kill all high frequency garble.
   I agree in using this sort of filtering for EACH chip.  Just putting 
one such filter on each board will again reduce the power supplied to 
each chip by a larger amount.  This is important for certain chips which 
need full input/output range.  Obviously if you only need +/-10V in or 
out, you can get away with the 100 ohm scheme without any worry.

   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
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