Filters...

[jamiewoody]

the lowpass filter seems to be one of the sweetest spots in a vintage synth!

a bandpass filter is a lowpass and a highpass.

would it be hard, using switches to be able to make a bandpass either lowpass, highpass or bandpass with the flip of toggle switches?!

[Circuitbenders]

Try and find the PAIA 4730 Multi Modal filter build manual. Its a module from the PAIA 4700 series modular synth and it has one input, but simultaneous low pass, band pass and hi pass outputs. Its also one of the most disgustingly flatulent filters i've ever heard.

If you can find the full build manual it has PCB layouts, schematics and a complete description of exactly what ever part of the circuit is doing.

[Gordonjcp]

The Steiner Synthacon filter has highpass, bandpass and lowpass *inputs* which is useful - especially since you can feed a signal into the highpass and lowpass input simultaneously and use it as a kind of frequency crossfade.

[jamiewoody]

here's the deal...i don't want to just copy a layout. i want to start simple and basic, and build on that. eat the elephant one bite at a time...

there are 4 basic vcfs...highpass, lowpass, bandpass and bandstop. i would assume that by switching between resistors, caps or something, i could change from highpass to lowpass or both....an lfo modulating between highpass and lowpass would sound PSYCHOTIC! wouldn't it?!! ;-)

[Circuitbenders]

. i would assume that by switching between resistors, caps or something

and thats why you need to copy something and learn how it works isn't it?  That sounds a lot like something my girlfriend would say, who seems to be uner the impression that you just stick a load of components in a box, and thats electronics 

[Bogus Noise]

Hahah, indeed, it's just like sculpture! Get one raw block of electronic, and take away all the bits that don't sound like a filter 

[jamiewoody]

i can see your point. i have a devry text book with some basic circuits for vcfs. they look like only a handful of components and no so difficult to build.

[Gordonjcp]

Well that's the thing - the Synthacon filter *can* mix from highpass to lowpass and back again, because it uses highpass, lowpass and bandpass *inputs* not outputs.  You can even feed the lowpass and highpass inputs to give an allpass filter, which is useful for phasing effects.

Here's an example of my Synthacon filter being fed by two synths (my Xiosynth and my Juno) playing the same riff as the filter is swept up and down.

http://www.gjcp.net/media/hilow.ogg

[Bogus Noise]

Actually, I've just remembered - if you mix a low pass signal output with an inverted copy of the original signal, you get a high pass. I've not put this into practice outside of the Autofilter in Logic, but I know some old analogue gear used this approach.