circuit design for resonant low pass filter wanted please

[smojo]

Saw these on Ebay and fancied making something similar. Does anyone know where I can find cct designs please.

M-Z3R0 - K FILTER V2 - resonant low pass filter.

[Dylan]

Great topic. I've been wanting a nice, simple, LPF schematic lately too. This one looks promising: http://www.magicmess.co.uk/electronics/6vfilter.php

[Circuitbenders]

do a search on here for synthacon, or search for synthacon filter or something on google

[smojo]

Thanks guys, the synthacon looks great but maybe a little too complex for me at the moment. The other design does look promising. I'm wanting it to hook up to some circuit bent toys or my nand gate oscillators to add a bit more colour to the sounds.

[jamiewoody]

i found and ordered these butterworth lowpass IC chips a while back. i wish i could find a citcuit for a lowpass filter with res using one of those. seems it would be much simpler, since the lowpass is already built!

[nochtanseenspecht]

ms20 filter has a simle design and is easy to clone. there is quite a lot of info on the net about it

[noob666]

http://ericarcher.net/devices/diy-lpf/

[Gordonjcp]

The Synthacon filter is barely any more complex than the Gakken filter ;-)

There are more diodes in the chain, giving a greater frequency range.  Like the MS20 filter and the Gakken filter, it is strongly affected by the DC conditions on the input - and in fact by the input signal!  Set it to be very resonant and stick in a low frequency sawtooth to hear what I mean.

Here is a pic of my prototype Synthacon filter, using bird's-nest construction: http://www.gjcp.net/media/filter.jpg
and this is what it sounds like (watch your speakers, the resonance gets out of hand): http://www.gjcp.net/media/filtertest.ogg