[sdiy] Weird filter in OB-Mx noise circuit

[mark verbos]

Aaron,

what you see there is Buchla's way of filtering down white noise into 
pink noise. It is similar to what he did in the 265  and 266 Source Of 
Uncertainties' noise sections.

Mark




Aaron Lanterman wrote:

> 
> I will now attempt to distract the list away from flame wars on jittery 
> VCOs with a new topic.
> 
> Look upon
> 
> http://users.ece.gatech.edu/~lanterma/obmx
> 
> and click on "Analog Section" under "Master Board."
> 
> At the bottom, you'll find 3 74HC164 setup as a feedback register thingy 
> forming a pseudonoise sequence. This gets passed through two filters in 
> cascade. The first is a Sallen-Key LP. The second is formed with two 
> op-amps in a weird configuration I've never seen before.
> 
> Anyone seen that filter structure before? What in the world is going on 
> there? That's not something I remember from the textbooks...
> 
> - Aaron
> 
> ----------------------------------------------------------------------------- 
> 
> 
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> and Demetrius T. Paris Junior Prof.    Voice:  404-385-2548
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