Archive of the former Yahoo!Groups mailing list: MOTM

----- Original Message -----
From: <konkuro@...>
How well does this filter track?
johnm

--Stooge Larry responds--
I have it on a freq. meter right now. Of course, it is designed to not
oscillate at very low frequencies to emulate the 904A (as I understand it
having never owned or even seen a 904A). So, I am starting with 220Hz. I
am increasing the input in even one volt intervals:
220 Hz
438 Hz
889 Hz
1804 Hz
3591 Hz

Obviously, VCO tracking would be:
220
440
880
1760
and 3520

So, for filter tracking over 5 octaves, it is as close as a filter gets as I
see it. Very little audible difference in pitch running a octave switch
through its steps. I was able to get the 220-440 octave perfect. But, the
high end was not as close as I have it now. So, I trimmed for a slight
error in the low end for greatly improved high end tracking. With the
circuit provided trimmer, you can really adjust it for what part of the
frequency range you want to be just perfect. Kudos Paul.

I have been sitting here for 1/2 hour playing with this filter. I finally
had to take the input oscillator out of the picture. This puppy is an
instrument in itself. "Oscillators? We don't need no stinkin'
oscillators." I have a patch set up a LFO gating an EG and the EG at the
1/v octave input. I am sitting here just playing the frequency knob at
about 120 BPM gates getting an awesome Frankenstein-like sound.

Tomorrow I am hooking a keyboard up to the 1/v octave input. I hear a demo
coming.

Now on to the issue of oscillation starting low in the res control range...
I have a pot in mine at R29 now so I can play with it and hear the
differences as I adjust it from the original 39K up to about 100K. For
self-oscillation effects, I really like the extra "meat" in the bottom thump
with the original 39K value in mine. Unfortunately, I am in headphones as
my better half is already asleep. But, tomorrow, I hook it up to the studio
performance amps/speakers. 600 watts bi-amped , 18" JBL instrument sub (bass
guitar cabinet - not some whippy home entertainment sub), eight 10" midrange
and 8 horn high end array. I'm calling the closest neighbor and telling him
to go out for lunch. :)

I will re-think my evaluation as I rid the property of rodents and other
small mammals. I might just mod mine and put a panel switch on for "hi-Q /
lo-Q" with lo-Q being some extra resistance that starts oscillation in a
more traditional range and hi Q shorting it out so I am back to the 39K
original resistor size for R29.

One thing is sure. I gotta have 2 of these for duophonic harmony with no
oscillators. :)

Bitchin' filter Paul. Not as pretty as a 440, but sometimes you just really
want to be nasty.

The only issue I have at all with this filter is that when you are passing
oscillator signals, the output is somewhat attenuated. But, the specs say
6V p-p output not 10V. And, I don't know if I'll even connect mine to an
oscillator again.

Stooge Larry