MOTM

I changed the resistor on mine, to 68K.  It broke into oscillation too
soon to suit me, even though that was the accurately modeled response to
the filter Paul was duplicating.  The only downside to the resistor
change is that with a signal input I cannot get as "pure" a sine wave
output from the filter at full resonance.  There always seems to be some
bleed/distortion from the input signal on top of the sine wave.  Without
an input this shouldn't be an issue.

John Loffink
jloffink@... 

> If you have one, I am curious as to the point on the res control where
> your
> stock 490s begin to self oscillate.  Paul was kind enough to clue us
in on
> which resistor we could replace to change that self-oscillation start
> point.
> I am wondering where others are and if they elected to do this, and
why?
>

> If you have one, I am curious as to the point on the res control where your
> stock 490s begin to self oscillate.  Paul was kind enough to clue us in on
> which resistor we could replace to change that self-oscillation start point.
> I am wondering where others are and if they elected to do this, and why?

I replaced the resistor on mine when I built it for the simple reason that I
used to have an Electrix FilterFactory, and it broke into oscillation at
about 12 o'clock on the knob. This really bothered me because it made the
rest of the knob rotation more or less useless to me. I figured that this
suggested I don't like filters that self-oscillate easily, and hence would
be happier with a modified 490. I'm happy with my modified 490, so I guess I
was right.

--Adam

Well, I know I am behind most of you on this one.  But, I finally fired up
my 490 filter tonight.  Paul made my brain hurt with the math in the theory
of operation docs.  But, it got much better once I heard that lovely sound.

The self oscillation tracking on mine was very good well above where Paul
said it would be good.  This is one nasty (in a good way) sounding filter.
It is certainly "different" than anything else in the MOTM stable (including
the 440 Low pass which I so dearly love).

If you don't have one, sell your kids and get one. :)

If you have one, I am curious as to the point on the res control where your
stock 490s begin to self oscillate.  Paul was kind enough to clue us in on
which resistor we could replace to change that self-oscillation start point.
I am wondering where others are and if they elected to do this, and why?

Kudos to Paul for another GREAT module.

Hey Larry and Group!

I, too, just got my 490 and built it.  I'm leaving it stock!  Mine 
goes into self resonance at about 4 1/2 which is fine with me.  The 
range trimpot was tweaked so that the upper frequency limit went just 
outside of my hearing (which is pretty high, considering my age)and 
allows me to distort the top end of the input.  Drives the cats NUTS!

Larry's right, people-this is a GREAT addition to your set-up.  I 
will definately get a second one.  While the 440 has greater range 
and a prettier sound, the 490 is VERY useful.  The interaction 
between the freq and res controls creates a lot of possibilities.

Chub-resonant at extra low frequencies

Mine starts at about 4 at certain frequencies.  I'm thinking about 
doing the mod because this is too low...

--- In motm@yahoogroups.com, "J. Larry Hendry" <jlarryh@i...> wrote:
> Well, I know I am behind most of you on this one.  But, I finally 
fired up
> my 490 filter tonight.  Paul made my brain hurt with the math in 
the theory
> of operation docs.  But, it got much better once I heard that 
lovely sound.
> 
> The self oscillation tracking on mine was very good well above 
where Paul
> said it would be good.  This is one nasty (in a good way) sounding 
filter.
> It is certainly "different" than anything else in the MOTM stable 
(including
> the 440 Low pass which I so dearly love).
> 
> If you don't have one, sell your kids and get one. :)
> 
> If you have one, I am curious as to the point on the res control 
where your
> stock 490s begin to self oscillate.  Paul was kind enough to clue 
us in on
> which resistor we could replace to change that self-oscillation 
start point.
> I am wondering where others are and if they elected to do this, and 
why?
> 
> Kudos to Paul for another GREAT module.

How well does this filter track?

johnm

>>>>
How well does this filter track?
<<<<

John,

The 490 is a really sweet sounding filter, but it is designed to 
emulate the 904A Moog closely. It's not set up for precision 
tracking, and even lacks a multiturn trimpot to dial it in. The best 
I've been able to do is to get it pretty good over 2-3 octaves. At 4 
to 5 octaves, mine is out about a quarter tone.

Moe

Hmmm. After reading Larry's post, it looks like it's capable of being 
dialed in better than I have mine. I may look into replacing the 
trimmer with a multiturn to make tuning it easier.

Moe

Larry wrote:

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

*******************

Very interesting.  Thanks for the detailed info, as I have been 
curious.  

I just stuck a frequency counter on my Synthesizers.com Q150 ladder 
LPF after reading your reply.  The results were:

220
440
882
1755
3456 

Like your filter, this one can be tweaked (though not internally) for 
greater accuracy in particular ranges.  It does have a nice sweet 
sine.  Interesting to compare.

johnm

----- 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

Clearly the more subtle review.  What a Stooge!
<snicker>
LH

----- Original Message ----- 
From: <mate_stubb@...>
The 490 is a really sweet sounding filter, but it is designed to 
emulate the 904A Moog closely. It's not set up for precision 
tracking, and even lacks a multiturn trimpot to dial it in. The best 
I've been able to do is to get it pretty good over 2-3 octaves. At 4 
to 5 octaves, mine is out about a quarter tone.

Moe

No, I think you are correct Moe.  I was not able to get perfect (Paul said
it would not be so).  As you dial the high end closer, the low end goes out.
So, you are correct, it's not like at all like a temp compensated filter.
In fact, I detect a slight bit of drift in mine.  But, I am truly excited
about the way this thing sounds.
LH

----- Original Message -----
From: <mate_stubb@...>
To: <motm@yahoogroups.com>
Sent: Friday, January 10, 2003 11:35 PM
Subject: [motm] Re: 490 filter


Hmmm. After reading Larry's post, it looks like it's capable of being
dialed in better than I have mine. I may look into replacing the
trimmer with a multiturn to make tuning it easier.

Moe




Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

Tracking/smacking....

Let's have a "Lucky Man" contest"!!

Paul S.
Beating the uSeq prototypes at 1AM....



----- Original Message ----- 

From: "J. Larry Hendry" <jlarryh@...>
To: "MOTM List" <motm@yahoogroups.com>
Sent: Saturday, January 11, 2003 1:40 AM
Subject: Re: [motm] Re: 490 filter


> Looks like Roger has his tracking quite nicely. I have never had the
> opportunity to play with the dot com filter.  But, I sure do like this one.
> :)
> Larry
> 
> ----- Original Message -----
> From: <konkuro@...>
> Very interesting.  Thanks for the detailed info, as I have been
> curious.
> 
> I just stuck a frequency counter on my Synthesizers.com Q150 ladder
> LPF after reading your reply.  The results were:
> 
> 220
> 440
> 882
> 1755
> 3456
> 
> Like your filter, this one can be tweaked (though not internally) for
> greater accuracy in particular ranges.  It does have a nice sweet
> sine.  Interesting to compare.
> 
> johnm
> 
> 
> 
>  
> 
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ 
> 
>

Looks like Roger has his tracking quite nicely. I have never had the
opportunity to play with the dot com filter.  But, I sure do like this one.
:)
Larry

----- Original Message -----
From: <konkuro@...>
Very interesting.  Thanks for the detailed info, as I have been
curious.

I just stuck a frequency counter on my Synthesizers.com Q150 ladder
LPF after reading your reply.  The results were:

220
440
882
1755
3456

Like your filter, this one can be tweaked (though not internally) for
greater accuracy in particular ranges.  It does have a nice sweet
sine.  Interesting to compare.

johnm

Paul S. wrote:

>Tracking/smacking....

Let's have a "Lucky Man" contest"!!<

Ugh. I don't think either .com or MOTM could ever be out-of-tune 
enough for that.

I've an idea for another type of contest, though.  I'll run it your 
way when the details are worked out...

johnm (I do like this sub-octave mux!)

Konkuro writes:
>>How well does this filter track?
johnm<<

Oh no. His first post. Run away. Run away.

Be forwarded that this list may suddenly become very verbose. As evidence look 
at the monthly number of posts in the Wiard forum. Notice that one month has 
many times more posts than all others. That's the month Konkuro was posting 
there.

And now for something completely different. A man with three buttocks.

-Elhardt

Elhardt wrote:

>Be forwarded [sic] that this list may suddenly become very verbose.<

Verbose? Never.  My writing displays the ultimate in economy.  
Observe:

MOTM-120
Inverts the dollar's motto:
"Out of one, many."

Note: The preceding MOTM-ku works only if you pronounce MOTM as MO-
tem, which I am told by its purveyor is correct.	
	
johnm