SynthModules

I assume the input attenuation resistors are 1%.  In a voltage divider 
with 10 volt input, the output could be 5 volts +/- 50 mV.  That's a 
100 mV difference potentially between channels.  100 mV is greater 
than a semitone so you could be off that much in sampling.  The only 
way to correct this would be to either trim each channel to calibrate 
it, or figure out how much it is off and use an offset multiplication 
in software.

The other possibility is the 10.666 volt reference as has been 
mentioned.  Sending a 1440, 1824, 2208, and 2592 to the 4 Dacs will 
result in 3.75, 4.75, 5.75, and 6.75 volts.  These should correspond 
to "A" octaves.  You can then adjust the 10.666 by beating a VCO 
against a 440 Hz reference, which I assume would be more accurate than 
trying to set it with a voltmeter.

Is your software quantizing?  If so, it wil magnify the error.

Dave



--- In SynthModules@yahoogroups.com, "Gary Chang" <gchang@...> wrote:
>
> After precisely calibrating the module, the new PSIM consistently
> outputs a sampled cv that is higher that the other PSIMs that are
> similarly trimmed.  I know that this is a moot point for those who
> have only one PSIM, and, for that matter, I can run Mike Firman's
> quadrature lfo program on the new one and use the older units that
> match for other stuff, but, I have to wonder - is there any 
difference
> between the old and newer PSIMs?
> 
> gary
> 
> "Brice D. Hornback" <bdh@> wrote:
> >
> > Gary,
> > 
> > You need to calibrate the reference voltage (there is a blue trim
> pot next 
> > to U5 labeled RT1) to exactly 10.666 VDC between ground and TP1.  
It's 
> > labeled on the PCB next to the test point.
> > 
> > Best regards,
> > Brice
> > 
> > ----- Original Message ----- 
> > From: "Gary Chang" <gchang@>
> > To: <SynthModules@yahoogroups.com>
> > Sent: Wednesday, November 15, 2006 12:22 AM
> > Subject: [SynthModules] Completed PSIM burning in....
> > 
> > 
> > >I assembled my new PSIM tonight (with the help of disassembling 
one
> > > that Brice built for me 2 years ago).  It works - but when run
> > > identical programs (gc-sah-sr-nq-djb.bas), the two modules 
output two
> > > different pitches when sampling the exact same source.
> > >
> > > Is there a way to calibrate the modules to be identical?
> > >
> > > gary
> > >
> > > p.s.
> > >
> > > Assembly really wasn't hard - and I have the module working now.
> > > Those of you who don't have their modules should really consider 
this
> > > option.... 8^)
> > >
> > > gc
> > >
> > >
> > >
> > >
> > > Be sure to check out the primary Web site at:
> > > http://www.SynthModules.com
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >
> > >
> > >
> >
>