Archive of the former Yahoo!Groups mailing list: MOTM

Thanks to Dave & Larry (who did all the work) here is how you need to modify
your MOTM-300 VCOs
to enable Soft Sync.

ADDITIONAL RESISTOR NEEDED: 4.7K (4700 ohms) 1/4W 5%

If you cannot obtain one, email me how many you need. I'll send them right
out.
All VCOs shipped after today will include this resistor and new
instructions.

You can also use a 5.1K (5100 ohms).

Step #1: ∗Unsolder∗ the inner conductor wire from the SYNC I/O left lug.

Step #2: Solder the 4.7K resistor - one lead on the top lug, the other on
the left lug. BE SURE the leads are short.

Step #3: Re-solder the coax inner wire TO THE TOP LUG.

That's it!!!!

HOW IT WORKS

You are adding a series resistance to the narrow sync pulse. The resistance
is added ONLY WHEN you plug a jack
into SYNC I/O. This additional resistance is enough to attenuate the sync
pulse so that the LM319 comparator fires
only when the sawtooth is near ground.

HOW TO TEST IT

You need to have 2 VCOs, EACH ONE with the mod.

Step #1: set each COARSE and FINE knob to 5. NOTHING into 1V/OCT or FM.

Step #2: set each SYNC switch to SOFT

Step #3: plug a patch cable between the SYNC I/O jacks

Step #4: you need to listen to the SINE out OF EACH VCO at once. Either use
a mixer or what I do
is run each VCO into Left or Right of my stereo AUX input.

Step #5: apply power. ∗CAREFULLY∗ listen as you move the FINE knob of 1 VCO
(doesn't matter which one)
You should hear the VCOs "lock" (no beats) then "unlock" (beats) as you
adjust the relative frequencies to the 2 VCOs.
It's not obvious at first, but pay close attenion and you can hear it. There
should be NO volume changes as you lock/unlock
(NOT TRUE with hard sync)

Again, sorry for not catching this at prototype and hat's off to Dave &
Larry. Ain't MOTM building fun??!?
I encourage everyone to listen to the new MP3 VCO/'120 samples on the
website. MP3 players are free everywhere:
I use WinAmp (www.winamp.com). Dave's analog drums are great! And check
Larry's "Theremin" patch. Joe Pavone
has 2 longer pieces that use all sorts of stuff. But I'm greedy! I want
more!

Paul Schreiber