Useful Urei Notch Filter???

[StephenGiles]

Look at this notch filtet from Urei - I start seeing VTL5C? in each frequency pot position plus LFO driver - any possibilities?
http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/UREI-560.pdf
Stephen

[toneman]

yes, Vactrols  instead of the dual10Ks.
but, this is a *notch* filter.
convert it to bandpass...then it would B a *parametric*.
check out the PAIA quad parametric.
been...there...done...that...
the filter in the MeatBall EnvelopeFilter is a Vactrolbased Multimode filter.
see the McMeat 4 the schemo.
Buchla made a synth filter using Vactorls ages ago...
C.Anderton did a BiFilter Fpllower with Vactrols also..
stayVactroled
tone

[StephenGiles]

I was thinking that maybe each notch filter could be tuned to a different frequency and just be a gentle effect.
Stephen

[puretube]

err, in short: if you`re talking about page 19:
note, that the pots are potentiometers, not variable resistors  :?:

[Eb7+9]

Thanx for posting Stephen !!

I see lots of potential with this thing despite the number of op-amps ...

Notch filters and bandpass filters both exhibit considerable amounts of group delay (phase shift) in the decades on either side of the cutoff frequencies ....

If you've got the "cut" controls modulating in intensity against each other it's hard to say what it would sound like ... it might simply produce a variable combing effect which might be very cool with proper adjustments ... try making it stereo, four stages per side, staggered frequencies ... (!)

I always wondered if the EMS frequency shifter they used on the backup vocals in DSOTM was done using the phasing part of a multi notch/band filter chain like this one ...

[StephenGiles]

Ton, what are you telling me there about the potentiometers?
Stephen

[puretube]

well, on page 14, there`s a block diagram, where the F-pots are wired as variable resistors (2 lugs);
but in the full schematic on page 19, the F-pots are wired as potential dividers (3 lugs);
so, without some mods, you can`t use the schem as is, IMHO, when you want to use vactrols ("2 lugs");

But have no fear: in fact those filters are ordinary state variables (SVF)...

With any SVF, that offers HP & LP outputs, you get a notch-function,
by adding the signals of those 2 outputs...

or: you get the same notch function, by adding the inverted BP output and the dry (input) signal... - this is the case with the UREI -

or subtract BP from dry...
or add inverted dry and BP...

read more about such filter-transformations from the synth freax  :wink:

[StephenGiles]

Thanks Ton, I didn't look at the circuit properly did I? Maybe a case for a very complicated PWM system, with 2 gates producing both an increasing and decreasing resistance for each potentiometer...........very complicated I should think!!!
Stephen

[puretube]

not neccessary: we`ll soon dig up a schem for you,
where you can use "2lug" var.res.(vactrols), to achieve the same...
(MuTron derivate...)

it has all been done before...

[StephenGiles]

Thanks, that would be great.
Stephen

[puretube]

funny how small the world, and how relative time is...

while I was searching synth pages to find a suitable schem before having to draw one myself, (was it tuesday?),I got some topic-reply-notification which distracted me, and then the whole bl**dy "vero-incident" started happening...

this noon, while trying to find back that schem, again I got a t-r-n that distracted me, and I decided to post a good-will answer there, first.
Of course, I had forgotten to log in, and when I hit the submit-button,
all was gone, and I started to re-type...

what to my surprise: Sir Giles had gotten right in between the post requesting me something, and my answer...

I hope not to have been the only one, who was glad about that posting  
had to do an extra translation there, which took some time,... now back to notches. (BTW: Stephen, I thought you were already in Sth. America).

Here is a nice simple example of a state variable (SVF), with the addition of an opamp for a notch-filter output like I had mentioned as one possible solution:
http://home.swipnet.se/cfmd/synths/schematics/svf1.pdf

just omit the LP/BP/HP buffers...
and put in vactroles for P1a/b...

over all, a nice weekend read (except for your wife (?)):
http://home.swipnet.se/cfmd/synths/friends/stopp/