[sdiy] battery powered resonant filter?

[Sowa Roman]

You know what, I was thinking about similar thing recently:
a battery powered modular. For filter you can use well known
discrete VCA (or rather OTA) cores like this one below:
http://membres.lycos.fr/romcio/m_pics/m_modvca.gif
(LOG is your CV input, LIN1 goes to +VCC)
this actually works with +/-12V, but by replacing opamps
with low power, rail-rail ones, you could run this circuit
from 2 battery cells, i.e. +/-1.5V I think it should work.
Common low power opamps work below +/-1.5V, and
there are devices working even at +/-0.9V. Of course output
amplitude will be reduced, but it should sound OK.
The transistor OTA core shown in the link needs no more
than +/-1V to work.
Make 4 of those, add capacitors to ground and buffers (again
low power opamps) between stages and you have nice filter
working at 3V. It should sound similar to famous SSM2044
designs (or was it SSM2040?).

This is unfortunately high component-count circuit.

Roman


__-----Original Message-----
__From: denshi [mailto:denshiblocks at yahoo.com]
__Sent: Wednesday, July 03, 2002 4:10 AM
__To: synth diy
__Subject: [sdiy] battery powered resonant filter?
__
__
__hello all!
__
__ive been perusing the internet for filter designs, but
__havent found what im looking for and was wondering if
__someone could help.
__id like to "graft" a simple resonant filter onto some
__of my older (read: knobless) keyboards but im not
__really comfortable messing with their power supplies
__to leach power for the filter.
__i guess im looking for a nice little filter
__(preferably korg style) that can be battery powered or
__power with a wall wart without too much hassle.  im
__still a novice at construction.
__thanks all!
__
__seth
__


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