MOTM

Paul, I finally got twenty minutes to myself last night to fire up the VCO I
built a month ago. This was just a bench-test-by ear-I didn't calibrate it
or use it in a musical context.

First of all, it passed the smoke test. Hooray! I guess I followed
instructions! That was my first concern-no fires and please please please
let *sound* come out of it!

In a nutshell, everything worked. You know that you're an analog synth
addict when you can entertain yourself for long minutes by manually spinning
the Pulse Width knob back and forth, grinning at the sound. Same goes for
pitch sweeping the VCO.

The tuning controls on my unit sound perfect to me-no scratchiness or
uneven-ness at all. Very smooth sweep. Using just my [thirty-something] ear
and a small speaker, it sounded to me that the Coarse tune control puts the
output supersonic at about "8," and subsonic below around "3". When I use
bright waveforms such as a sawtooth or narrow pulse, I can hear the upper
harmonics go "tick...tick...tick..." even when the fundamental has gone
way-far south. Very nice range. And like I say, smooth sweep.

The Width control seems, by ear, to have almost a 'flat spot' around 50%
where the pulse sounds square even with a little play in it. In other words,
it sounds square from around 47%-53% on the dial. Maybe that's just my ear,
or maybe that's intentional. It works out well, though. I also notice that
the Width control doesn't go to "100%" or "0%" where the sound would
disappear at either extreme-it stays just inside of the margins of
audibility. I imagine applying PWM would push it over the edge if desired,
but the knob covers a good comfortable range. Very nice.

Anyway, sorry for the delay in getting back to you with this report. Chalk
up one more very happy camper! I'm eager for my next shipment!

Note that the WIDTH control is like that *on purpose* as I didn't want
anybody
thinking it was "broken" when the pulse goes away (to DC, actually).

I think the 'flat spot' is just your ear's inability to distinguish. There
is no circuitry to to that
intentionally.

Paul S.

I figured that the PW limits _were_ part of the design. My dear old MS-10's
Pulse Width control, for example, seems to go to DC at about "2" and "8"
which doesn't leave much of a range to fine tune the setting. I much prefer
your design.

You're probably right about the "flat spot" being subjective. In fact, it
may actually be related to the above-on my other synthesizers, finding a 50%
pulse is kind of finicky *because* the useable range/angle of the control is
so limited. With the MOTM-300, there is more sweep range, so there's finer
control and that may help give the impression that there's some play in
setting the right width. Whatever the case, I'm very satisfied. It's as if
the desired setting just 'falls into place' when you adjust that knob.

One more thing, and maybe I'm crazy here... The pots that you use seem to
have a very wide angle of rotation-greater than 270 degrees. When I look at
the knobs on my other machines, it seems to the eye that their "0-10" angle
is less than 270. It's almost like... like your knobs 'go up to eleven.' :-)

		-----Original Message-----

		Note that the WIDTH control is like that *on purpose* as I
didn't want anybody thinking it was "broken" when the pulse goes away (to
DC, actually).
		I think the 'flat spot' is just your ear's inability to
distinguish. There is no circuitry to to that intentionally.
		Paul S.

They are 300 degree pots! Good eyeballs!

Paul S.

In a message dated 10/14/99 7:00:06 AM, Ken.Tkacs@... writes:

>One more thing, and maybe I'm crazy here... The pots that you use seem
>to
>have a very wide angle of rotation-greater than 270 degrees. When I look
>at
>the knobs on my other machines, it seems to the eye that their "0-10" angle
>is less than 270. It's almost like... like your knobs 'go up to eleven.'
>:-)

I noticed this when using a cheapo pot on one of Paul's scrap panels I got 
from him. The knob on the cheapo pot only went to 9, so maybe the Spinal Tap 
reference isn't that satirical. Or maybe on a scale of 1 to 10 MOTM is an 11.

JB