[sdiy] HP from LP ? -> Mother-32

Andrew Simper andy at cytomic.com
Fri Aug 4 04:52:18 CEST 2017


On 3 August 2017 at 22:46, Michael Zacherl <sdiy-mz01 at blauwurf.info> wrote:

>
> So, it seems Moog have taken a shortcut as well, to get this "other”
> filter response?
>
> OTOH, the Moog 904B is a true HPF but with no resonance control.
> Is there a practical reason for that?
>
>
The blurb seems to imply it's a proper moog high pass like the 904B, but
clearly it isn't by the reviewers comments. Resonance works with the 904B,
but since the cutoff is increased as the transistor non-linearity is hit
it's a good idea to limit the feedback signal before it gets sent to the
input of the filter. In a regular moog ladder the cutoff is decreased with
the non-linearity. I've modelled a resonant Moog high pass filter in my
plugin The Drop, it's called PRD HP.

The Moog Ladder 500 module looks like the real deal. It has a hp / lp
switch, and 12 / 24 dB slope selectors, so I'm guessing this is a proper
moog high pass. I would love to see the schematic for it since the topology
of the two filters is quite different - they may just have two entire whole
filters inside - which would be a shame since you can't use them both at
once to make a mega bandpass filter.

Cheers,

Andy
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