MOTM

I use this patch that I posted recently:

Borrowed from an old idea in Electronotes (GLAP):

Requires 1 VCA, 3 mult segments and 2 mixers with inverting attenuators (two
MOTM-830 first sections or two Oakley Multimixes)

Mults not listed for clarity.

Patch signal to be panned to VCA input, Mixer 1 input 2 (full +) and Mixer 2
input 2 (full +)
Patch VCA output to Mixer 1 input 3 (full -)
Patch Mixer 1 output to Mixer 2 input 3 (full -)
Patch 0 to 5 volt control source to VCA CV In
Mixer 1 output is first panned output
Mixer 2 output is opposite panned output

John Loffink
The Microtonal Synthesis Web Site
http://www.microtonal-synthesis.com
The Wavemakers Synthesizer Web Site
http://www.wavemakers-synth.com


> -----Original Message-----
> From: Richard Brewster [mailto:pugix@...]
> Sent: Saturday, September 11, 2004 2:28 PM
> To: MOTM List
> Subject: [motm] Panning VCAs
> 
> Hello all,
> 
> I have been experimenting with two-channel stereo panning and wanted to
> share my thoughts and get yours.  My 1980's era homebrew Electronotes
> synth used a pair of EN linear VCAs, for which I provided a panning VC
> input.  That did some convenient internal voltage conversion.  All the
> VCAs I use are similar to the MOTM-190 in taking a control voltage in
> the range of zero to +5V, with zero volts equating to zero gain and +5V
> to unity gain.  (I have two 190 VCAs, a modified Blacet Quad VCA/Mixer,
> and a Quad Low Pass Gates.  The latter is yet to be built, but I will
> calibrate it for a five volt control range.)  Let's say we want to pan a
> signal from left to right in stereo.  We need two VCAs, both taking the
> same signal input, with one going to the left and the other the right
> channel output.  We want to smoothly pan from one side to the other and
> back.  Stands to reason that we need one control going from zero to five
> as the other goes from five to zero volts.  Now my first problem is how
> to get a five to zero volt signal, starting from a zero to five volt
> one.  I can't just use an inverter, because the result will be going
> zero to minus five.  I have to add an offset of five volts.  In my synth
> I have several ways to do this.
> 
> I modified my MOTM-800 EGs so that the minus output goes from +5 to
> zero.  (Hint:  It takes one resistor.)  So I could use an 800.  But the
> exponential wave shape may not always be what I want for panning.
> Another module I can use is one of my Blacet EG2070s.  These also have +
> and - outputs like the MOTM-800.  The Blacet by design goes from +5V to
> zero on the minus output.   The upper voltage is adjustable, because
> Blacet standard VCA controls are zero to +10V.  I adjust mine for the
> five volt range to match MOTM.  The Blacet EG is a linear device and can
> self-cycle, so I have a pretty good panning controller there.  But what
> if I need my Blacet EG for something else?   A third candidate is my
> super-custom MOTM-OMS-820, which I modified to add a zero to +5V self
> cycle mode.  Again, that is way overkill for this purpose.  *I just want
> an LFO that goes zero to +5V!*   Blacet's new LFO has zero to 10V and
> 10V to zero outputs.  It is built for panning the Blacet VCAs.  But I
> don't have one of those LFOs!  And if I did, I would have to modify it
> for a five volt range.  Back to my 1980's synth.  The panning input took
> a zero to five volt signal and did the conversion internally.  I've seen
> many VCA panners with this feature.  I suspect the long-awaited MOTM
> panning VCA has it.
> 
> That's not the end of it.  For proper panning you want a smooth
> transition of the sound field.  It should appear to be moving gracefully
> left to right, without extreme level changes.  This requires the right
> sort of response in the VCA and the right control contour.  I've been
> playing with different combinations.  Using a sine wave as the control
> with an exponential VCA response seemed pretty good.  (That takes a
> MOTM-320R and two of my Mixer-Comparator modules to rig up.)  I'm over
> my head here and just dabbling.  Surely some of you folks know a lot
> more about this.  I haven't researched my Electronotes archive yet on
> this one (I tend to drop those heavy binders on my toes!).
> 
> So what do you folks use for VC panning?
> 
> Cheers,
> 
> Richard Brewster
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