[sdiy] Good 24db/oct HP-LP-BP-Notch filter Schematics ??

Tom Wiltshire tom at electricdruid.net
Thu Mar 6 00:27:43 CET 2014

On 5 Mar 2014, at 23:08, Michael Zacherl <sdiy-mz01 at blauwurf.info> wrote:

> On 5.Mar 2014, at 23:45 , Mattias Rickardsson <mr at analogue.org> wrote:
>> Seems almost impossible.
>> Could it be a major typo? :-)
> ;-) 
> http://www.analoguesystems.co.uk/pdf/RS110.pdf – first page, last paragraph …
> m.

I'm not sure that document makes anything clearer. It says:

"The RS110 consists of a two channel audio mixer followed by four, parallel, resonant filters with voltage controlled frequency and a unique "insert" point in the feedback path that generates and controls resonance."

Now, I seriously doubt that there are genuinely four separate, parallel 4-pole filters on that PCB. Although that would be one way to do it, it would be very inefficient. So what exactly *are* they talking about?

My bet is a simple 4-pole Moog-style ladder (hence the talk of a "discrete" filter with "no filter chips") with several mixers doing pole-mixing to get the various responses (that's the "parallel" part).

Hasn't anyone on here got one? Can't someone just pull one out of the rack and have a look?!?


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