[sdiy] HP from Ladder

[Sean Ellis]

I traced the ladder inputs from my modular, the 303 filter was similar:

http://s270.photobucket.com/user/Shudder11/media/moog_hp.jpg.html


The notch is a simple grounded wiper on a pot with associated resistors. It's pretty boring TBH, a switch or cascading 2 like the MS20 would be more useful.

________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Gordonjcp <gordonjcp at gjcp.net>
Sent: Tuesday, 1 August 2017 8:09 PM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] HP from LP ?

On Tue, Aug 01, 2017 at 12:10:48AM +0000, Sean Ellis wrote:
> I have seen a way to inject the signal into the ladder to get a highpass response, Tom Gamble was the first person I saw do this but I cant find the original message (was on SDIY sometime around 2000). I have gotten highpass from the 303 filter in the same way:
>
> https://soundcloud.com/tensiontype/303-highpass1
>

Well hang on, how does it work in the Sallen-Key topology like in the
Steiner Synthacon?  I know that's not a ladder - it looks like one
opened out flat to balance the diode chain, but it's fed differently -
but there must be some way to do it.

The neat thing about that is it has both lowpass and highpass *inputs*
so it can act like a kind of frequency crossfader:

http://gjcp.net/mp3s/hilow.ogg

--
Gordonjcp MM0YEQ

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