The Cyndustries List

Richard,

For your testing, what is the output impedance of your Mixer-Comparator?
Unless it is the range of ~100 ohm or less, it may cause some of the error
you are seeing.

An MOTM 820 VC Lag has a properly designed output for accurate 1V/oct
tracking.  You may want to put your voltage source through that for your
measurements.

For any broad tracking between ZO and other VCOs, I am thinking you may need
to use a soft sync function between them.  No matter how accurate the VCOs,
there will be differences in beating through the audio range.  Because one
VCO is used as a modulator, the beating may sound more prominent than two
VCOS that are simply mixed in parallel.  

John Loffink
The Microtonal Synthesis Web Site
http://www.microtonal-synthesis.com
The Wavemakers Synthesizer Web Site
http://www.wavemakers-synth.com


> -----Original Message-----
> From: The_Cyndustries_List@yahoogroups.com
> [mailto:The_Cyndustries_List@yahoogroups.com] On Behalf Of Richard
> Brewster
> Sent: Sunday, February 26, 2006 6:27 PM
> To: The_Cyndustries_List@yahoogroups.com
> Subject: Re: [The_Cyndustries_List] ZO 1V/Octave calibration
> 
> Thanks, Cynthia.  I found the trimpot easily.
> 
> I ended up with a setting close to the original factory setting. But I
> was not able to fix a problem of the ZO tracking sharp in the lower
> octaves of the high range. I started down this calibration road because
> I noticed that the ZO and the MOTM-300 being used as the FM source in
> the starter ZO patch were not tracking each other well.  The beats were
> quite noticable.  I spent a couple of hours taking measurements, after
> setting the 1V/oct trimpot.  Here's what I found.
> 
> I measured with a digital voltmeter and a digital frequency counter.
> For comparison I performed the same tests on the MOTM-300 VCO.  The
> results were all obtained by the same method and instruments, using the
> same power supply.  I created a 1V source by a mixer with bias (my own
> mixer-comparator) and measured for 1V at the 1V/oct input jack.  For
> each reading I dialed up a frequency, applied 1 volt and recorded the
> new frequency, which ideally is double for the next octave.  For the ZO
> I did this in all four combinations of High/Low Bias and High/Mid
> range.  I only measured what I could dial up that started in the audio
> range. Each number pair below represents the HZ value before and after,
> so 30/60 means 30HZ/60HZ.
> 
> Low Bias/Mid Range
> 30/60 - right on
> 60/119.8
> 
> Low Bias/High Range
> 30/66
> 60/123.2
> 120/241.5
> 240/480 - right on
> 480/957
> 
> High Bias/Low Range
> 30/60.2
> 60/120 - right on
> 120/239.7
> 240/478.4
> 
> High Bias/High Range
> 30/66
> 60/124
> 120/243
> 240/482
> 480/960 - right on
> 960/1916
> 1920/3825
> 
> MOTM-300
> 30/60 - right on
> 60/120 - right on
> 120/240 - right on
> 240/480 - right on
> 480/960 - right on
> 960/1918
> 1920/3834
> 
> The ZO tracking isn't bad, but it isn't great either.  The ZO starts out
> on the low end tracking more than one octave per volt (sharp), passes
> the sweet spot and starts going flat gradually.  By contrast the
> MOTM-300 tracks perfectly over about six octaves and then also start
> going a little flat.  Now this flatness on the high end may be by
> design, due to psycho-acoustic effects, I seem to recall. I'm not a
> music VCO expert. But sharpness on the low end isn't good.
> 
> For my ZO the tracking is accurate over at best about three octaves.
> The lower octaves track better in the low range and the higher octaves
> track better in the high range.  This was a useful finding.  Of course I
> tested only my own ZO, so I can't say whether this is the general
> character of a ZO or not.  Still, I would be interested to hear from
> other ZO owners whether they are able to replicate my findings.
> 
> -Richard Brewster
> 
> http://www.pugix.com
> 
> 
> 
> 
> 
>