[sdiy] newbie with some questions

[Neil Johnson]

On Mon, 10 Dec 2001, Rhen, Kris wrote:
> I'm curious why?  The Paia 9700 is setup that way.  What's the difference
> between
>
> V-------+-------+
>         |       |
>         M1      M2
>
> and
>
> V---+-------M1
> |
> +-----------M2
>
> Same voltage level reaches both, right?

Sorry, Kris,  *WRONG* !!!!

Your diagram is far too simple to model the Real World (TM).  It actually
looks something like:

         L      R           L     R
V(+)---////--[XXXX]---+---////--[XXXX]--+
                      |                 |
                      M1                M2
         L      R     |     L     R     |
V(-)---////--[XXXX]---+---////--[XXXX]--+

Where "L" and "R" and the inductance and resistance of the power supply
wires respectively (note: I have not included parasitic capacitance
either).  So in effect M1 _can_ have an effect on M2, and vice versa,
which may not be desirable, especially if they're both oscillators in
which case they'd lock into sych. when they're both close to each other's
frequency.

This not only happens in wires but on PCB layouts too, which is why you
sometimes see weird-looking spidery traces running around a board,
spanning out from a few key points.

So, in some simple circuits you may get away with this wiring scheme, but
any half-decent analogue synth will be susceptible to this, especially
oscillators where we notice subtle pitch changes quite well!

Hope this helps,
Neil

--
Neil Johnson :: Computer Laboratory :: University of Cambridge ::
http://www.njohnson.co.uk          http://www.cl.cam.ac.uk/~nej22
----  IEE Cambridge Branch: http://www.iee-cambridge.org.uk  ----