[sdiy] D/A accuracy - voltage is floating?

[Tim Parkhurst]

My first suspect would be the quantizer. Is it a commercial unit? How
accurate is it? Maybe it's receiving a voltage from the D/A that is just on
the threshold between two notes and a teeny bit of noise or a small
fluctuation in the voltage will make it jump to one note or another.

Either that, or the occasional stray cosmic ray is causing it :)

Tim Servo
"Imagination is more important than knowledge." - Albert Einstein




> -----Original Message-----
> From: Bret Truchan [mailto:clone45 at hotmail.com]
> Sent: Friday, January 30, 2004 11:31 AM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] D/A accuracy - voltage is floating?
> 
> 
> Hello friendly DIY people!
> 
> This is probably an easy question.  I've built what's *basically* a small
> sequencer using a microcontroller and a serial D/A converter.  In short,
you
> clock the microcontroller which sends values to the serial D/A converter.
I
> take the output of the circuit, plug it into a quantizer, then out to
> control the pitch of my VCO.  (aka - it generates a little tune)
> 
> The output of my D/A converter seems to be, oh, not-so-accurate.  The same
> little tune plays over and over again, but sometimes one or two notes in
the
> tune get quantized differently.  I believe that the output of the D/A
> converter is floating a little bit.
> 
> I have two questions.
> 
> #1.  Is it possible that the output of my D/A converter is floating a bit?
> It's a TLC5620IN.  I don't see any noise on my power lines.  I've got
> filtering capacitors all over the place.
> 
> #2. If I skip the quantizer and go straight into the VCO, my ear is having
a
> tough time deciding wether or not I can _hear_ the fluctuations in pitch.
> Is there some fancy technique that I can use to record the voltages coming
> out of my circuit so I can tell if they're really fluctuating?  I have an
> oscilloscope, but that doesn't help me much.
> 
> Thanks a ton in advance!
> - Bret
> 
> Oh, here's some extra information:
> 
> 1. The external clock signal is going through a voltage clamp made up of a
> zener diode and two resistors.  If I pay close attention to my power lines
> (magified a LOT), I can see teensie noise introduced by the incoming clock
> signal.  I don't know how to remove the noise.
> 
> 2. I'm using an Atmel Mega8 microcontroller.
> 
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