[sdiy] Debugging Hammond filter circuit

[Scott Gravenhorst]

Aaron Lanterman <lanterma at ece.gatech.edu> wrote:
>
>On Apr 24, 2010, at 11:40 PM, Scott Gravenhorst wrote:
>
>> if the JFETs are a problem, H11F1 (F2 F3) might work instead...
>
>Well, in the 4-section C-JFET cascade, the J201 do seem to make a 
>nice highpass filter with a nice control range. I think it's the 
>use of the highpass filter in the feedback loop that is strange 
>and sensitive. The more I look at it the more it seems that the 
>feedback level has to be carefully balanced. 
>

Yeah, I see, not really a problem.  It's my birthday --- beer today! sorry.

It _looks_ interesting, but weird too.  Sort of an uncommon/unconventional 4
pole cascade without interstage buffering.  The circuit allows easy voltage
control because the JFETs are grounded on one end.  I'm guessing that is why
the capacitors and JFET cascade was placed into the feedback loop so as to get
easy voltage control of a lowpass filter.

I will certainly be interested to see if this makes a decent lowpass VCF once
all the bugs are worked out.

-- ScottG
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-- Scott Gravenhorst
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