[sdiy] modern AD/DA chips?

[Tom Arnold]

On Thu, May 07, 2009 at 09:22:17AM +0100, Tom Wiltshire wrote:
> Sorry if this seems like pointing out the bleeding obvious, but how  
> do you know the errors are all in the MIDI->CV?

Simpler to check then you think. :-)  
If I drive them all with the same CV, they stay pretty amazingly close in
unison.   Its when driven from seperate CVs that the error rears its dead.

> It'd be a pretty rare VCO that hit the same pitch repeatably to the  
> degree you're talking about, wouldn't it, even if the voltage was  
> spot-on?
> And you say this was with the dead simplest VCO, so I assume without  
> multiple layers of temp compensation and error correction and  
> whathaveyou. Surely the VCO can't be relied on to be *perfectly* in  
> tune each time?

By dead simple, I mean swatooth core with no waveshaping.   From Ian Fritz's
site, http://home.comcast.net/~ijfritz/sy_cir2.htm.  The VCOs are very
repeatable.  I hav stripped and ditched them as I was having problems with
the VCOs hard syncing and the eventually fix was not pretty.  I know what to
not do next time though...

Anyhow, in this particular case I was seeing very predictable errors on the CVs
themselves.  When you should see, say, 4vdc on everything, and you see 3.996
4.000 and 4.004, and all that happens is the numbers stay the same but move
around, yeah, thats your DAC :-)

( well, okay, in one case one time it was my HP3456, but I caught and solved
that problem before blaming *too* much gear )

-- 
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 - Tom Arnold       -  Free Synth DIY webspace http://www.sdiy.org 
 - SynthGeek        -
 - BBD Fanatic      -  "...is it a virus, a drug, or a religion?" 
 - echo evho wjxo   -    Juanita Shrugs. "What's the difference?" 
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