Vactrol based VC-PANNER

funkyfarm · Last edited by funkyfarm on Sun Apr 08, 2007 7:28 pm; edited 2 times in total

Can anyone confirm that there must be a mistake in the voltage control stage of this design, found at Mark Verbos' ?

http://www.simple-answer.com/DIY.html

PANNER :

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On left transistor base, I guess this 4k7 resistor tied to ground to be 22k, same as the resistors which sum the cv input and the trimmed centre-reference ?

I would say the control voltages should be summed as in the cross-fader schematic, which makes sense...

CROSS-FADER :

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vtl5c3 · Posted: Sat Mar 24, 2007 7:56 pm Post subject:

I can't say one way or another how well it will work, since I haven't tried it myself. Scott Stites however, used that crossfader as a starting point for his Multiphase project. You might want to take a look at the crossfader section at:

http://mypeoplepc.com/members/scottnoanh/birthofasynth/id19.html

Good luck. If you build either the X-fader or the panner, let us know how they turn out.

Romeo

funkyfarm · Posted: Sun Mar 25, 2007 10:40 am Post subject: Green / Red / Green / Red !!!

I would say that it is "normal", when cv signals are summed, to solder all together via 22K resistors (or 47K or 100K or else...) and then adding another 22K one (same value) tied to ground...am I wrong ?

It works with a 22K.
This design is killer !!!

I've added a simple inverting buffer at the input (with two 47K) and lowered the last stage (120K/39K -> gain is 3) to GAIN =2 (with 47K and one 100K as feedback resistor) to have it 10V peak-to-peak.

Then I've add another green LED (when LEFT output is active), and now that rocks ! Wink

Green / Red / Green / Red !!!
and :
Green AND Red lightining around the centre position !

funkyfarm · Posted: Sun Mar 25, 2007 10:49 am Post subject:

What the first 1K input resistor is here for ?
Lowering it could allow to make the last stage gain down to 1,5 or less, instead of 2 (as S/N ratio decreases with high amplification)

(I guess no...but as the 10K tied to ground are part of the panning core, there would be no other way decrease "a little bit less" the overall gain of this design.)

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funkyfarm · Posted: Sun Mar 25, 2007 12:29 pm Post subject: NO GAP IN THE MIDDLE

vtl5c3 · Posted: Sun Mar 25, 2007 7:45 pm Post subject:

to do what's referred to as "Equal Power Panning" you need a special driver for the VCAs. As far as I know, Serge and Plan B are the only commercial systems that offer this (as well as Buchla). It's nice that with the Buchla circuit, you need very few parts to accomplish this.

funkyfarm

vtl5c3 · Posted: Mon Mar 26, 2007 9:55 am Post subject:

Thanks for the samples. That sounds very nice indeed. I like the first one with the slow pans. With headphones on, it goes right through my head.
cyclops

fonik · Posted: Mon Mar 26, 2007 10:47 am Post subject:

yes, absolutely convincing.
do you see any chance to redraw the schematics according to your modifications? that would be great.

vtl5c3

funkyfarm · Posted: Mon Mar 26, 2007 4:57 pm Post subject:

funkyfarm · Posted: Mon Mar 26, 2007 5:05 pm Post subject:

funkyfarm · Posted: Wed Mar 28, 2007 1:31 pm Post subject: Subject description: extras

I guess two units on a single board would be cool (sharing the same psu decoupling and 5V buffers)

Two panner output mixers should be added for more complex stereo patch (for example sending one sound L-R 100% and the second 40% or else)
No pot needed. Only two extra sockets (Mix L & Mix R)

I'm also wondering about adding a comparator at CV input, for "1-to-2 analog switch" style mode.
The trick would be to generate +5V or -5V whenever the cv waveform is.
Then, panner circuitry internally set to zero (centre), main potententiometer could be substituted for comp's THRESHOLD... (DPDT or TPDT switching involded ?)

PS : even my EH-30 modular's DG201 analog switches sometimes clip with audio waveforms...
http://home.swipnet.se/~w-49485/e_eh30.htm

funkyfarm · Posted: Wed Mar 28, 2007 7:24 pm Post subject: Subject description: 4 to 2 to 4

I guess this could be a killer stereo module...

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Because of my panel layout, I can lay only six potetiometers ; so initial settings would be shared by the two panner units.
Maybe no dual pot is required for controlling both (as ends are buffered +5V and –5V).
Different initial settings can be achieved using an external mixer with bias (via PAN 2 CV).

Hooked to PAN 2 CV "initial setting" resistor, the switch LINK/INV derivates PANNER pot. cursor signal for inverting process ; INPUT 1 signal can be « offset » saying by 40% left while INPUT 2 is 40% right…

PAN 2 CV is normalized to PAN1 CV input signal ; maybe PAN 2 CV should be an inverting attenutor…

I would add two mixer (no pot) for PAN L and PAN R sums.
Those master LEFT and RIGHT outputs would be available at PANNER 2 outputs when nothing plugged into PANNER 1 outputs !
(PANNER 2 outputs sockets would be fed by the mixers ; normalized jack sockets allow bypass of PANNER 1 outputs mixing)
Or two extra sockets can be simply use…
This requires one whole TL074.

With this config you can have four sources cross-faded into two channels, themselves panned into stereo space ! ! !

Don’t know if an « analogue mode » would be fine…

What would be cool, with Scott’s permission, is to get some superb-good-looking-fonik-style PCB layouts Wink

for Dual VC-PANNER and Dual CROSS-FADER units !

Each use same-looking CV circuitry and I guess -/+5V buffers could be shared.

Small pcb,
Compact panel layout,
Efficient module Very Happy

krisp14u · Joined: Nov 11, 2006 Posts: 206 Location: uk

fonik · Posted: Thu Mar 29, 2007 2:14 pm Post subject: Subject description: 4 to 2 to 4

Scott Stites · Posted: Fri Mar 30, 2007 10:36 am Post subject:

Wow. Would you believe I have just such a module at home already?

I should back-track a bit. Years ago, I had this idea for a module incorporating both designs in a similar manner. I scratched it out in Express Schematic and sent it to Jeff Pontius. He actually built a module out of it, though it was just a scratching - I never proofed it on breadboard. Well, it's a schematic I'd never release, because even a few months later I realized it wasn't a great implementation and should be reworked, but I just shoved it to the side (I had no idea Jeff was moving forward with it - he was a powerhouse of module building in that day, getting done in days what it took me months to do).

The last time I saw Jeff, he gave me the module to work on - it didn't work because he followed my schematic to a T. I told him I'd get it working, as soon as the current project was off the plate, but I wished I'd have jumped right on it, because Jeff was gone a month and a half later. I'll always regret that. He did a nice job on the panel design (it was a Schaeffer panel).

Anyway, thanks for posting the samples - I'd actually breadboarded the panner, and had it working - but never actually *heard* what it did - I just looked at it on the scope (didn't have the technological advancement of stereo anywhere in reach at the time).

Of course, you don't need my permission to build any module or make any board - neither design is mine - they are Don Buchla's (unless Mark made any alterations). If you want to use my MultiPhase mods, please breadboard before you commit - those worked in that particular situation, but I'm not so sure as a general purpose crossfader it will work that well. Probably will, but certainly confirm.

Haven't looked at it lately, but if it uses the particular bipolar attenuator design I prefer, I've gone through a sea change with those. Rene Schmitz originally turned me onto it (though he'd picked it up someplace else). It originally used a 1M pot, but I found whenever I looked at the output on a scope, even at full attenuation fast transients came on through. I reduced it down and down and down until 10K, which works perfectly, but requires a buffer to keep input impedance at 100K (at least for my standard).

The implementation for that can be seen on my Triple Wilson SVVCF control board on my SVVCF construction page. BTW, as an OT aside, I finished that monster Tuesday night. It was, by far, the most intense build I have ever done in my life - literally made me question my sanity - five boards driving a 2U wide panel with twenty pots and thirty jacks, with nearly half the jacks switching jacks is a tall order, as it turns out. But it was worth it.

Cheers,
Scott

funkyfarm · Last edited by funkyfarm on Sun Apr 08, 2007 7:33 pm; edited 1 time in total

funkyfarm · Posted: Sat Mar 31, 2007 3:01 am Post subject:

funkyfarm · Posted: Sun Apr 08, 2007 6:31 pm Post subject:

The dual panner module is finished !

There is about twelve TL72 (or equivalent) populated...

tests are here

Both panner are in "switch mode" :

for CV IN 30K resistor, signal from CV IN jack is swapped for CV comparator output
and main PANNER pot cursor is routed to the threshold of the comparator.

So now, only one output is active at one time, and the PANNER pot can shift the duration of the two states...

Slow vactrolish switching but I guess it's cool.

3Mo of Blinking LEDs Cool

Stereo comes from a dual STEINER filter :
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Scott Stites · Posted: Tue Apr 10, 2007 10:51 am Post subject:

Nice samples! Thanks for posting this - sounds like a good module to have around.

Cheers,
Scott

funkyfarm · Posted: Wed Apr 11, 2007 7:51 am Post subject:

Thank you Scott !

You can consider this as yours !!!

But this is only half-module Wink

funkyfarm · Posted: Wed Apr 11, 2007 8:08 am Post subject:

maybe someone should keep close to your value for resistors (10k instead of 47k for the reversible CV or inverting buffer) ; for non-inverting cv input, I only put a potentiometer as a divider but with 47kA, strange things occured when no jack plugged (there is a "small" 30k resistor after...)...I put 10KA, then it started groovin' Cool

funkyfarm · Posted: Sat May 19, 2007 8:28 am Post subject:

mediatechnology · Posted: Sat May 19, 2007 7:01 pm Post subject:

Here's a matrix panner I've posted elsewhere. You can use Vactrols for the pot:

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It's constant power.The THAT1240s have internal 0.005% laser-trimmed resistors permitting high amounts of attenuation. If Vactrols (two) were used in place of the pot, the image would be centered when they were of equal value. Looks like the LED differential drive circuits cited in the previous posts could also be used here.

Things get very interesting when the insert is used with compressors, filters and delay.

There's a discussion here:

http://www.prodigy-pro.com/forum/topic-22036.html