Tube Moog (Was:Re: Website update)

[Malcolm B McIntosh]

I actually tried one.... It had 3 ladder rungs (thus a 12 pole filter, I
hoped).  I could not get the thing to sweep very much at all, maybe from
50Hz to 500Hz.  Now mind, I was just hacking at it....  Since I was
interested in seeing if the pentodes could be used as a filter core in
the ladder configuration, I just used an opp amp back end as the
differential amp section.  One time, (and one time only), I got a really
nice sounding resonance feedback.

Tried a 4 pole with 5 twin triodes.... Same result.

Malcolm (still crazy)

patchell wrote:
> 
>     Hmmm.....what about a pentode ladder filter......that might cut
>down on the number of diff amps.  That would be a sight, a moog ladder 
>filter built out of tubes....(slap..) well, it was just a thought.
> 
> René Schmitz wrote:
> 
> > At 20:13 27.09.00 -0700, patchell wrote:
> > >    Maybe this is a pretty naive question, and please remember, I 
> > >have never used tubes in anything, so I might be ignorant......
> > >
> > >    Correct me if I am wrong, but doesn't the screen grid on a 
> > > pentode tube vary the transconductance of the tube?  Seems like 
> > > there should be someway of exploiting that to tune a tube based 
> > > filter.
> >
> > Right. That should be possible. Varying the screen grid voltage does 
> > shift the DC-quiescent point. It could lead to a differential design, 
> > with plenty of diffamps. Looking at my VTVCA, imagine a cap from 
> > plate to plate of the pentodes whose screengrids are steered. Several 
> > of these two pentode stages could be cascaded.
> >
> > Bye,
> >  René
> >
> > --
> > uzs159 at uni-bonn.de
> > http://www.uni-bonn.de/~uzs159
> >
> >
> 
> --
>  -Jim
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