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

Mattias Rickardsson mr at analogue.org
Thu Mar 6 18:24:45 CET 2014

Only 7 transistors in total, so no Moog ladder.
2 x 10n, 2 x 1n caps.


On 6 March 2014 18:14, Tom Wiltshire <tom at electricdruid.net> wrote:
> On 6 Mar 2014, at 17:08, Neil Johnson <neil.johnson71 at gmail.com> wrote:
>> Tom Wiltshire wrote:
>>> It's hard to see, but that's a CA3046 tranny array, and I can see at least two CA3080's on http://fa.utfs.org/diy/rs110/DSCI0012.JPG
>>> My bet is on Moog 4-pole with CA3080's acting as output amps for the stages. The Taurus design is the simplest of the Moog output amps, and that'd make the circuit simpler. The TL072's are the mixer amps and the CV handling and whathaveyou.
>> Since one CV input is set to 1V/oct my guess would be the CA3046 is
>> used for expo conversion.  More importantly the lack of capacitors -
>> for a 4-pole design one might expect to see 4 equal valued capacitors
>> for the four poles.  I see the two red WIMAs down by the CA3080s.
>> Unless the schematic is available it might be fun to reverse-engineer it?
> Isn't that what we're doing?!
> Do you think it's 2-pole then, Neil?
> I agree that I'd expect to see 4 equally valued capacitors, and four CA3080s if my theory were correct, and so far, we've only found two of each. The other two could be on that lower PCB that we can see so well, but I wouldn't have done it like that. I'd have had the filter and CV stuff and input mixer on one board, and all the output mixers and output jacks on the other. Which it doesn't look like. So..dunno.
> They do claim it's 4 pole specifically, but as was pointed out, the information appears to have been written by someone charitably described as "non-technical".
> T.
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