[sdiy] battery powered resonant filter?

[Theo]

Diode-bridge VCF and VCA like for example used in korg MS50 and 770 work
fine on battery power.
A stack of 6 diodes needs only ~0.6V*6= ~3.2V for full CV range.
I use those in some guitar stomp-boxes.
External CV input runs straight into a voltage divider,
so the circuits accepts normal +/-10V CVs while running from a single +9V
(battery) supply.

HTH,
Theo


From: Sowa Roman <Roman.Sowa at upc.com.pl>

> 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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