[sdiy] Re: Inexpensive 16 bit DAC?

[Tim Parkhurst]

What about the trick Oberheim used on the Matrix 12? Or was it the OB
series? Anyway, they used an 8 bit DAC, but in places where they need higher
resolution (VCO fine tune, fer example), they used a fairly simple trick to
get (approx) 12 to 13 bit resolution:

Set DAC Vref to its 'normal' level. Say +10V
Convert 8 MSB, store analog result in S/H
Set DAC Vref to lower level. Say 1V
Convert 8 LSB, add analog result to MSB conversion.

Basically, you take two 8-bit samples, but you change the Vref for the LSB
sample and add the two results. The voltage levels I have listed above are
only examples, but you get the basic idea.


Tim (lots of basic ideas) Servo

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

**********************************


> -----Original Message-----
> From: Scott Gravenhorst [mailto:music.maker at gte.net]
> Sent: Thursday, April 28, 2005 10:13 AM
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Re: Inexpensive 16 bit DAC?
> 
> Harry Bissell Jr <harrybissell at prodigy.net> wrote:
> >As drawn, no advantage. Possiblt a little better
> >symmetry, have to check the source / sink currents
> >of the buffer to see if it would be truly
> >symmetrical...
> 
> I can't speak for the 4066, but I know that the 4069UB is
> spec'd as having symmetrical transistors.  It's one of the
> reasons I like them.
> 
> >By extension, you sould replace the "+12V" going
> >to the switches with a precision reference... or even
> >a variable reference... making a multiplying DAC.
> >(of course negative voltages are out).
> 
> Truly.  For me, it was mental gymnastics.
> 
> >
> >Back to my ORIGINAL complaint and name of the
> >thread... with 1M and 2M resistors you are going to
> >not, NO WAY make your own 'inecpensive' 16 bit
> >converter.  The archetecture is there, but the
> >implementation is NOT !!!
> 
> I am so out of touch, is this because they must be precision
> resistors and prec. resistors of that value range are more
> expensive?
> 
> 
> 
> >--- Scott Gravenhorst <music.maker at gte.net> wrote:
> >> It seems to me that the analog switches are overkill
> >> and could be replaced by
> >> a CMOS inverter gate (or buffer) per bit.  It looks
> >> to me that the switches
> >> are simply providing a solid 12 volts or a solid
> >> ground to one end of each
> >> resistor.  I'm really not sure why a 4069UB
> >> wouldn't work as well at less
> >> than half the part count.  Ok, you would want to do
> >> TTL to CMOS level
> >> conversion, but still it would be fewer parts.  A
> >> 4066 is a bidirectional
> >> device but you are using it as a unidirectional
> >> device which is why I think a
> >> 4069UB design would work just as well.  The 4069
> >> would be powered from +12
> >> and ground, the output of each gate hits the
> >> resistor.  If the whole thing
> >> were powered by +5 and ground, it would be even
> >> simpler.
> >>
> >> Is there some advantage the 4066 provides that I'm
> >> not seeing?
> >>
> >> "Ray Wilson" <raywilson at comcast.net> wrote:
> >> >
> >> >Here is a DAC with CD40106 and CD4066 chips. I have
> >> demo'd 4 bits but you
> >> >could go as many as you had patience to build.
> >> >
> >> >Ray
> >> >
> >> >----- Original Message -----
> >> >From: "KA4HJH" <ka4hjh at gte.net>
> >> >To: "Bob Weigel" <sounddoctorin at imt.net>
> >> >Cc: <synth-diy at dropmix.xs4all.nl>
> >> >Sent: Wednesday, April 27, 2005 3:24 AM
> >> >Subject: Re: [sdiy] Re: Inexpensive 16 bit DAC?
> >> >
> >> >
> >> >> >Usually you have to tell them that you are like
> >> working on something
> >> >>>where you might actually BUY some chips to get
> >> samples...or does Analog
> >> >>>just hand them out to anyone?  I could have been
> >> getting samples all
> >> >>>along for the project I'm working on from
> >> microchip but I haven't even
> >> >>>had time to ask for them and I feel bad doing it
> >> because we really don't
> >> >>>need them except that that company is out of
> >> money I guess so maybe we
> >> >>>do :-). -Bob
> >> >>
> >> >> They may ask you a few simple questions, like
> >> "What's this for?" or
> >> >> "What's
> >> >> the goal of the project?". So you just answer
> >> "experimental interface
> >> >> design for musical instrument" or something lofty
> >> you've daydreamed about
> >> >> but will probably never get around to. Talk like
> >> a junior in college--half
> >> >> clueless but you know some buzzwords.
> >> >>
> >> >> Maxim is another one you want to hit up...they've
> >> got good stuff...
> >> >>
> >> >> --
> >> >>
> >> >> Terry Bowman, KA4HJH
> >> >> "The Mac Doctor"
> >> >>
> >> >> "You'd PAY to know what you REALLY think"--Dobbs
> >> >
> >> >
> >>
> >>
> >---------------------------------------------------------
> >> - Where merit is not rewarded, excellence fades.
> >> - Hydrogen is pointless without solar.
> >> - What good are laws that only lawyers understand?
> >> - The media's credibility should always be
> >> questioned.
> >> - The only good terrorist is a dead terrorist.
> >> - Governments do nothing well, save collect taxes.
> >>
> >> -- Scott Gravenhorst | LegoManiac / Lego Trains /
> >> RIS 1.5
> >> -- Linux Rex         | RedWebMail by RedStarWare
> >> -- FatMan: home1.gte.net/res0658s/fatman/
> >> -- NonFatMan: home1.gte.net/res0658s/electronics/
> >> -- Autodidactic Master of Arcane and Hidden
> >> Knowledge.
> >>
> >>
> >
> 
> ---------------------------------------------------------
> - Where merit is not rewarded, excellence fades.
> - Hydrogen is pointless without solar.
> - What good are laws that only lawyers understand?
> - The media's credibility should always be questioned.
> - The only good terrorist is a dead terrorist.
> - Governments do nothing well, save collect taxes.
> 
> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
> -- Linux Rex         | RedWebMail by RedStarWare
> -- FatMan: home1.gte.net/res0658s/fatman/
> -- NonFatMan: home1.gte.net/res0658s/electronics/
> -- Autodidactic Master of Arcane and Hidden Knowledge.
> 
> --
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> 

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