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

Michael E Caloroso mec.forumreader at gmail.com
Fri Aug 4 06:45:06 CEST 2017

On the Voyager, resonance only worked on the LP VCF in BP mode.  The
HP VCF is the simple inversion/sum trick but with resonance disabled.


On 8/4/17, Dave Leith <dave.leith at gmail.com> wrote:
> Moog Voyager had both HP and LP and they could be configured to bandpass
> with adjustable width. I don't remember what resonance did in bandpass
> mode....it's been a while :-)
> On Thu, Aug 3, 2017 at 7:52 PM, Andrew Simper <andy at cytomic.com> wrote:
>> 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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