[sdiy] Buchla 296 lowpass topology

Matthew Arthur mathewarthurtech at gmail.com
Thu Dec 1 03:17:28 CET 2022

Sorry for the double reply, but I've actually got a pretty good idea why
the circuit was chosen.

I believe R7, the 2.2k resistor adjust the q without significantly changing
the frequency.

On Wed, Nov 30, 2022, 8:59 PM Matthew Arthur <mathewarthurtech at gmail.com>

> I think it's a 2 stage lc low pass filter followed by a modified active
> bridged t.
>  My simulation of the active stage shows that the addition of the 4.7u cap
> and 8.2k resistor to ground change the bridged-t so that it allows some low
> frequency signal through.
> Very 1960s design. Can't really see why it was chosen though, seems a bit
> overcomplicated to me
> On Wed, Nov 30, 2022, 8:29 PM Lanterman, Aaron D via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>> Taking a peek here:
>> https://modularsynthesis.com/roman/buchla296/296%20Schematics.pdf
>> 15 of the 16 bands consist of MFB bandpass filters.
>> But the lowpass is… something else? Look at the far right where it says
>> “alternate section for board 1” — anyone recognize that topology? I have a
>> suspicion that it’s something standard that I’m just not seeing because of
>> the way it’s drawn.
>> Aaron Lanterman, Prof. of ECE, Georgia Tech
>> My blog on Education and Innovation:
>> https://edupocalypsenow.wordpress.com
>> My blog on Electronics and Programming:
>> https://lantertronics.blogspot.com
>> My YouTube channel on Electronics and Programming:
>> https://www.youtube.com/c/lantertronics
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