MOTM

OK, at Dave B's request (see bottom paragraph below), I took the sync test
and passed.  As Dave indicated, mileage may vary (and mine did a little
bit).  But, I came to the same general conslusion.  However, I have only 2
VCOs to work with, so I couldn't do the 4 VCO test.  DANG, there goes that
cash thing again.

Anyhoos, here is what I found:

1.  The pitch interval selected to sync to has some inpact on the values of
resistance that will work.  Some intervals will sync up with looser
coupling (like octaves).

2.  Regardless of interval, the over syncing syndrome described by Paul
(medium sync) happens at about the same resistance between VCOs.

3.  For me, reliable soft sync occurred over a range of about 5.5K to 18K
total resistance beteen the two sync connections.  Some intervals had more
spread, but this range worked with ALL intervals I tested.

4.  At around 5.1K my VCOs went into over sync and to the same note.

5.  Above 18K VCOs would sync and slip, sync and slip.

Dave's formula, which worked fine for 4 oscillators applied to my numbers
would yeild a median of 11.75K -12K ohms, divided by 2 (one in each MOTM)
yeilds 5.9K - 6.0K ohms as the medium.  The range would be
3K to 9K.  I played with this set up for soft sync and it was rock solid. 
Not once did it not do what I expected.

So, this is just FYI in case any of you motm'ers out there want to wire up
a resistor in a patch cord and get soft sync to work pending a
recommendation, hopefully in the not to distant future, from our uncommonly
quiet synth guru Paul.

Like Dave said.  DON'T MODIFY THE MODULE.  This has been a test.  Had I
been a real engineer, I would have said something intelligent.  Instead, I
can only confirm what Dave has already told you.  <grin>

And, yes Dave.  Soft sync is VERY cool.  However, not nasty like that hard
stuff.  :)

Larry Hendry
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From: daveb@...

Yippee!!!! I played with some resistors tonight and got all 4 of my
MOTM-300s soft syncin' across a tuning range of up to 4 octaves. I'll tell
you what I found - your mileage may vary, of course. I'd like others to try
this - it's 100% safe since I didn't mod the VCOs at all.

Soft sync did not work at all for me before I started - I had the "medium
sync" syndrome Paul spoke of where the two independant pitches disappear
into 1 pitch.
 
First I wired a 200k pot between the hot lugs of 2 spare jacks (and gnd to
gnd, natch) and plugged patchcords up between the jacks and 2 VCO sync
inputs (both switches set to "soft"). Then I varied the pot to add
resistance into the sync patch and found a range which allowed soft sync to
work. Below this resistance range I got "medium sync", above it there was
no sync. I used 2 oscillators tuned 1 octave apart, detuned to 3-5 beats
per second. I measured all combos of 2 oscillators synching, took the
largest minimum and the smallest maximum resistance. I found that for a 2
oscillator connection, that adding a resistance of between 4.5K ohms and
19.5K ohms works for my 4 VCOs. Take the median and divide that by half to
split into 2 resistors (one for each VCO sync input), and you get about 7K
ohms added resistance per VCO.
 
Next I tested soft syncing of multiple VCOs. I took a mult panel that I
recently made up, and modded one of the mults to add a 5.1K resistor (cause
that's what I had laying around) from each jack's hot lug to a common point
(NOT ground). So patching all the 4 VCO sync inputs to this mult adds about
10K per patch. You can play with the resistance values without modifying
your module.
 
All four synced up! I set up a patch with fundamental, octave, octave +
fifth, and two octaves + a third. With soft sync what you get is the
individual pitches remaining, but because there are no beats, your ear
blends it all together into a new timbre.
 
My VCOs aren't tweaked to track perfectly yet, and I'm running them on
different MIDI/CV channels which adds some error. If I play low notes, it
sometimes doesn't sync until it phases through a cycle. I'm going to tweak
the resistors some more, lowering the value to attempt to get a slightly
more aggressive sync.

I'd like some others to try this to see if my experience is typical or not.
Let's give Paul some data to work with. What resistances work for you (or
does adding resistance NOT work at all)? Please DO NOT mod your VCOs - I
don't want somebody to tear up a trace and I DON'T claim that this is the
permanent fix.
 
Enjoy - soft sync is very cool!