extending the range above or beyond what a programmble synth normally sees...

[J.D. McEachin]

At 09:43 PM 7/6/96 -0500, DJMaytag wrote:

>when you go to write a patch into a programmable synth, it scans all the
>resistors and switches and anything else relevent to the patch (right?). now

It uses a multiplexed AtoD convertor to scan thru all the pots on the front
panel (unless it's a CS-80 ;-), and it reads the voltage across each one,
which is stored as a 4-16 bit value, depending on the synth (yes, the PAIA
Proteus stores a measly 4 bits!).  To restore the patch, each value is sent
to a DtoA convertor, which is demultiplexed and sent to the appropriate
portion of the synth circuit as a voltage.

>i'm wondering that if were to mod the synth, say to increase or decrease the
>resistance of a pot HIGHER or LOWER that what it normally should be, would
>that be taken into consideration when you write that patch into memory? or
>does it know to only look at a certain range of resistance?

If you're thinking about replacing front panel pots, forget it.  You may
wind up overloading the power supply, and besides, it won't do a damn bit of
good - it's only looking for a voltage, usually between 0-10VDC (don't even
think about changin that).  If you're thinking about changing the scaling
resistors in the synth circuit, you need to have at least a rudimentary
knowledge of what you're doing and a willingness to replace the shit you
blow up while experimenting.  In the case of most digitally controlled
analogue polysynths, there tend to be fewer places you can tweak, due to the
use of CEM or SSM chips.

>i guess what i'm wondering is if a could somehow decrease the frequency of
>an LFO in a synth by changing the resistance of the LFO freq knob on a synth
>(probably my p-600).

If I remember correctly, the P600 LFO is generated by the CPU, so you're
looking at a massive hacking job to change it.  To do this you'll need to be
prepared to give up a major portion of your free time, know how to read a
schematic, how to hack really bad code w/o a clue as to how it works, and
how to put up with assholes who question whether you're _really_ doing what
you're doing.

Good luck.

JDM
Synthcom Systems, Inc.
http://www.synthcom.com/