MOTM

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!

Rocket Man

Major cool Dave. I will be trying this tomorrow night and reporting to the
list.

Here's a thought: Suppose one wanted to add this mod to the VCO without
changing the circuit board. Looks to me like it could be tacked right on
the back of switch # 3 in series with the orange wire (although that would
not be the prettiest thing).

Paul, A CDR with audio from Dave B and Larry H MOTM set ups in in the
mail tomorrow morning. I will be burning it tonight. All the sampling is
already done.

Larry H

> 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.

---snip---

> 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!

> From: "J. Larry Hendry" <jlarryh@...>

> Here's a thought: Suppose one wanted to add this mod to the VCO without
> changing the circuit board. Looks to me like it could be tacked right on
> the back of switch # 3 in series with the orange wire (although that would
> not be the prettiest thing).
>

That was the first place I thought of adding resistance, but totally
external is better when you are experimenting. If this added resistance
turns out to work as a permanent solution for most cases, hopefully the
extra resistance can just be added into R21, allowing you to replace it with
a higher value - but I'd want Paul to look at it first.

Tacking the resistor to the switch is not desirable from a reliability
standpoint. Only 1 side of the resistor is mechanically supported, and
vibration from moving could eventually cause the resistor to fail. If a
person absolutely has to do a repair like this, you want to tack the body of
the resistor down with RTV somewhere (side of the switch, in this example)
to prevent vibration from cracking the leads.

It would probably work OK, but in your heart you would know that deep in the
soul of your beautiful MOTM system is a festering, cancerous, abcessed, jury
rigged slimy hack, and you would awake screaming in the night hoarsely
shouting "I'm sorry! I'm so sorry! I'll never do it again!! I'll fix you the
correct way right now, my beloved..."

Err, never mind.

Dave Bradley
Principal Software Engineer
Engineering Animation, Inc.
daveb@...

Paul--
What is your official word on this???

--Todd

> Hi List and Dave.
> great job Dave it worked for my 2 vco's using about the same resistence
> value as you.
>
> thanx
> Gur Milstein

Hi List and Dave.
great job Dave it worked for my 2 vco's using about the same resistence
value as you.

thanx
Gur Milstein