MOTM

Happy New Year All!

As promised, here are my observations/comparisons of the MOTM 300 VCOs and
MOTM 420 VCF vs. some Moog modular stuff.  This is all very subjective and
it is certain that YMMV!

The setup:
- Encore Expressionist MIDI/CV Converter -> Moog Modular CV/Trigger inputs
- CV -> Moog 901A Oscillator Controller controlling a few 901B Oscillators 
- CV -> Moog 904A Low Pass Filter
- Same CV mult'd -> two MOTM 300 1V/Oct inputs and MOTM 420 1V/Oct input
- MOTM 300 outputs and Moog 901B outputs -> Moog mixer panel
- One mixer output -> MOTM 420 input and the other output -> Moog 904A
filter input
- Both filters input -> the same Moog 901 VCA
- One Moog 911 EG -> the VC inputs of both filters
- One Moog 911 EG -> the VC input of the Moog 901 VCA
- Output of the VCA -> trunk lines -> mixer/power amp
For the waveform tests, I ran the output of the Moog mixer panel directly
to the VCA.  The Moog modules are all R.A. Moog modules from around 1969.

MOTM 300 VCO vs. Moog 901B VCO:
Note: There is a big difference in functionality between these two!  The
Moog 901B has a wide range but isn't terribly linear.  Mine have recently
been calibrated and do well over 5 octaves with the 8' octave range
setting.  This doesn't hold true for the other octave range settings.  The
901B has no PWM, no Sync, and no linear FM. The output of the MOTM 300 is
very hot, about twice the level of the 901B.  I'd love to do these same
tests with some Moog 921 oscillators if I could find some!

- Sawtooth Waves: No major difference.  The MOTM might be a tad
brighter/buzzier but it was really hard to judge.  The mid harmonics might
be coming out more.  When mixed together, the beating between these two
oscillators is *really* intense.  I had them beating about once every 10
seconds but the sweep caused by the phase interaction was like a very wild
PWM with a pronounced almost sawtooth modulation.  I could not get this
kind of beating between like oscillators on the Moog or the MOTM.  There is
something really wild happening when combining these different oscillators
running off different power supplies.

- Sine Waves:  Very small difference.  The 901B sine had a few more
harmonics in it making it sound slightly more nasal than the MOTM.  Both
seemed to have a few extra harmonics so I might be picking up a tad bit of
distortion elsewhere in the signal path (VCAs, mixer panels, etc.) but it
was quite musical.

- Triangle Waves: There was pronounced difference between these waveforms.
The MOTM had a more "hollow" sound while the Moog seemed to have a
"rounder" sound.  They are both recognizable as triangle when compared with
Saw and Pulse but there is a difference.  I dare say that I think I prefer
the Moog triangle wave in this case because it sounds a bit "fatter" than
the MOTM.

- Pulse Waves:  These are certainly different.  The Moog Pulse Width
control needs to be set fully to the right to get close to a square wave.
Even at that it doesn't sound as fully "square" as the MOTM VCO in the
center of the dial.  There is a tad bit more buzz in the Moog VCO, leading
me to believe it isn't quite square.  At the narrowest setting (fully left
on the Moog and fully right on the MOTM), the sounds were very close but
the Moog had just a bit more nasal quality to it.  The MOTM PW that is
fully to the left is quite different from any of the Moog PW settings.
Sweeping the PW on both sounds quite good although the Moog PW is
equivalent to only the right half of the MOTM PW.  Both are quite good
sounding!

That's enough for now.  I'll write up some more notes on the filter tests
soon.  The filters are *very* different beasts!  I hope this is at least
interesting.  I found it quite educational.  If I had a better
oscilliscope, I'd be interested in seeing some of the waveforms but all I
have is an ancient Heathkit that is wonderful for the price I paid for it
(nothing) but can only tell you that what you are seeing is a sawtooth wave
vs. a triangle wave....

	Eric

>
> MOTM 300 VCO vs. Moog 901B VCO:
> Note: There is a big difference in functionality between these two!  The
> Moog 901B has a wide range but isn't terribly linear.


The RA Moog tracking is 10 times *worse* than a '300.


 >Mine have recently
> been calibrated and do well over 5 octaves with the 8' octave range
> setting.  This doesn't hold true for the other octave range settings.

That's be cause he had truble finding good capacitors.

 > The
> 901B has no PWM, no Sync, and no linear FM. The output of the MOTM 300 is
> very hot, about twice the level of the 901B.  I'd love to do these same
> tests with some Moog 921 oscillators if I could find some!

That's probably true: the 921Bs I had were about 6V pk-pk.

>
> - Sawtooth Waves: No major difference.  The MOTM might be a tad
> brighter/buzzier but it was really hard to judge.  The mid harmonics might
> be coming out more.

That's the OP-275's fast slew rate. The MOTM has more harmonic content.

>  When mixed together, the beating between these two
> oscillators is *really* intense.  I had them beating about once every 10
> seconds but the sweep caused by the phase interaction was like a very wild
> PWM with a pronounced almost sawtooth modulation.  I could not get this
> kind of beating between like oscillators on the Moog or the MOTM.  There
is
> something really wild happening when combining these different oscillators
> running off different power supplies.


What you are hearing is the Moog not tracking with the '300. It's not the
power supplies.
This is just the difference in *relative* tracking with the Encore as the
"reference".


> - Sine Waves:  Very small difference.  The 901B sine had a few more
> harmonics in it making it sound slightly more nasal than the MOTM.  Both
> seemed to have a few extra harmonics so I might be picking up a tad bit of
> distortion elsewhere in the signal path (VCAs, mixer panels, etc.) but it
> was quite musical.

No argument here.

>
> - Triangle Waves: There was pronounced difference between these waveforms.
> The MOTM had a more "hollow" sound while the Moog seemed to have a
> "rounder" sound.  They are both recognizable as triangle when compared
with
> Saw and Pulse but there is a difference.  I dare say that I think I prefer
> the Moog triangle wave in this case because it sounds a bit "fatter" than
> the MOTM.

Again, the MOTM waveforms are closer to ideal. But again, this is
subjective.


>
> - Pulse Waves:  These are certainly different.  The Moog Pulse Width
> control needs to be set fully to the right to get close to a square wave.
> Even at that it doesn't sound as fully "square" as the MOTM VCO in the
> center of the dial.  There is a tad bit more buzz in the Moog VCO, leading
> me to believe it isn't quite square.  At the narrowest setting (fully left
> on the Moog and fully right on the MOTM), the sounds were very close but
> the Moog had just a bit more nasal quality to it.  The MOTM PW that is
> fully to the left is quite different from any of the Moog PW settings.
> Sweeping the PW on both sounds quite good although the Moog PW is
> equivalent to only the right half of the MOTM PW.  Both are quite good
> sounding!


I never understood Moog's "offset" with PW on the modular. Very strange.

Keep it coming Eric! (and Ben V. can compare as well).

Paul S.

At 11:28 PM 1/1/00 -0600, Paul Schreiber wrote:
>From: "Paul Schreiber" <synth1@...>
>
>>
>> MOTM 300 VCO vs. Moog 901B VCO:
>> Note: There is a big difference in functionality between these two!  The
>> Moog 901B has a wide range but isn't terribly linear.
>
>The RA Moog tracking is 10 times *worse* than a '300.
>
Yes, I forgot to mention that during the testing, I had to tweak the Moog
oscillators a few times to get them back in pitch.  I only had to do this
once for the MOTM oscillators and that's because I turned the wrong knob!
I have a digital tuner that I plug into the sine wave output of the
oscillators to keep an eye on the oscillator tuning at any time.

>
> >Mine have recently
>> been calibrated and do well over 5 octaves with the 8' octave range
>> setting.  This doesn't hold true for the other octave range settings.
>
>That's be cause he had truble finding good capacitors.
>
Hmm, does that mean if I found some good capacitors, I would be able to
improve the tracking over octave switches?

>>  When mixed together, the beating between these two
>> oscillators is *really* intense.  I had them beating about once every 10
>> seconds but the sweep caused by the phase interaction was like a very wild
>> PWM with a pronounced almost sawtooth modulation.  I could not get this
>> kind of beating between like oscillators on the Moog or the MOTM.  There
>is
>> something really wild happening when combining these different oscillators
>> running off different power supplies.
>
>What you are hearing is the Moog not tracking with the '300. It's not the
>power supplies.
>This is just the difference in *relative* tracking with the Encore as the
>"reference".
>
So this is just a minor difference between the tracking?  The funny thing
was that I couldn't detune either the MOTM or the Moog oscillators to get
the kind of phase cancellation that I got with the MOTM and the Moog.  Yes,
it changed slightly as I went up and down the keyboard but it was very
pronounced in that the oscillators almost cancelled each other out.
Perhaps this has something to do with direction of the saw waves?  I'll
check this out.  Perhaps one is saw up while the other is saw down?

	Eric