In praise of 4-pole filters

[Paul Marossy]

I bought a Sequential Circuits Pro-1 that is still in a bit of a state of disrepair, but for now it processes external signal just fine through the ext-in jack.  It has a 4-pole lowpass filter built around a Curtis CEM3320 chip, harnessed to a very decent envelope-follower, gate/trigger extractor and ADSR transient generator.

I had never played guitar through a 4-pole lowpass before, and I have to say it is REALLY nice.  And, confirming Stephen Giles' frequent suggestion, using a gate and transient generator provides a whole universe of sounds beyond what the average envelope-controlled filter will produce.  Using a slow attack, moderate envelope modulation, , and some chorus, you can get some truly lovely pads.

Funny, I was just thinking about what that sort of filter might sound like with guitar after I restored to full working order a hand me down Korg Polysix synth last week. I was looking at parts of the schematics and thinking about what it might sound like with a guitar passing thru it. I would of never thought about it unless I had read about this LFO thing out of a keyboard that Frank Zappa was using to get that perculating sound you can hear on "Canarsie" off of the "Shut and Play Yer Guitar" set. I don't want that kind of sound exactly, but it would be cool to get those sorts of polyphonic sounds like the Polysix can produce on a guitar. Not sure if it's really possible to adapt any of that stuff to guitar, but the thought was in my head the last few days...

[Keppy]

I made a pedal with 2xLM13600 using two of the two-pole Butterworth filters from the datasheet, adapted to +/-9v and guitar signal levels. It sounded pretty clean. It wasn't an envelope filter though, just VC lowpass.

[bwanasonic]

The only Prophet (Prophet VS) I ever owned didn't allow external processing, but did have an analog curtis-based 4-pole filter. I always wanted a Frostwave Resonator to pair with my Frostwave Blue Ringer. I am a total sucker for juicy filter sounds. I have always felt it should be a law that synths have a 4-pole analog filter.

[liquids]

The only Prophet (Prophet VS) I ever owned didn't allow external processing, but did have an analog curtis-based 4-pole filter. I always wanted a Frostwave Resonator to pair with my Frostwave Blue Ringer. I am a total sucker for juicy filter sounds. I have always felt it should be a law that synths have a 4-pole analog filter.

I believe paul perry of frostwave, has said here that the frostwave resonator was (is?) just a slavish copy of the MS-20 filter, for which schematics are not unobtanium, if the project interest you.

[aron]

The MS-20 has a radical filter! I have the Korg Kronos and the MS-20 emulation is crazy!!!!
Listen to this:

MS-20 lead, filters

[space_ryerson]

The Korg Monotron also has the MS-20 filter in it, and the schematics are readily available for that as well. It's only a one page schematic, so it shouldn't be hard to find the VCF on it!

OT: Aron, how do you like the Kronos?

[aron]

Using it tomorrow. Love it.

[petemoore]

  Sounds like your fluent with the bend stick or you made that trippy clip using a guitar.
   It's not a 'string sound' but did sound like 6 [or so] strings controling the pitch, very freaqey sounding note-switcher-lead BTW.

[Jazznoise]

The Korg Monotron also has the MS-20 filter in it, and the schematics are readily available for that as well. It's only a one page schematic, so it shouldn't be hard to find the VCF on it!

OT: Aron, how do you like the Kronos?

It's also 50 quid to just buy, but yes the filter is exceedingly quick and dirty to get a hold of! http://www.korg-datastorage.jp/Manual/monotron_sch.pdf

A quad op amp, 3 transistors and a fet and you're there. Diode clipping, always had it in my head that the MS-20 filters awesome distortedness wouldn't literaly be clipped like that!