[sdiy] Re: Inexpensive 16 bit DAC?

[Bob Weigel]

Well..not *all* of them have to be :-).  But I've never built one and so 
I'm thinking of potential problems as I go along here.  If you just run 
out of a latch; each pin into a resistor with all the other sides tied 
together to an op amps inverting input with feedback resistor to create 
a summing node, then you have another potential problem.  What if the 
load differences affect the unregulated output of the latch? :-).   That 
might turn out to be a serious problem. 
    Probably with a mosfet output drive chip the differences would be 
negligable so long as the minimum impedence was kept above a few K.  And 
the LSB's resistor accuracy's diminish in importance of course.  The LSB 
can be a 20% tolerence resistor in fact, right?  And there will be a 
stepping of the accuracy needs all the way up to something like .001% to 
be ultra safe..however .002% you wouldn't notice a difference and you 
could get away with .005% units which actually are available for the 
first two most significant bits.  (they usually are tighter than the 
specs advertised...and if you select them with a precision meter like my 
hp I think you can pull it off :-) )  Anyway...then you have a couple 
that need to be .01% probably since that's the only tolerence you'll 
find I'm guessing....  Then some ..4 of them unless you can find a .05% 
and then three .1%, and three 1%'s or one and a couple 2%'s if you can 
find them and then the rest can be 5% tolerence unless I'm just totally 
not thinking right :-).  -Bob

Paul Perry wrote:

>----- Original Message ----- 
>  
>
>>Will I get enough (or good) performance from a DAC
>>built with discrete components (high accuracy
>>resistors and a good vref) ? 
>>    
>>
>
>If you are wanting 16 bit accuracy, then you need
>to use resistors accurate to 0.001%, I think.
>Which makes $20 for a PCM54 look cheap!
>
>But I can't think of anywhere in an analog synth
>you would need 16 bit accuracy, off hand.
>
>paul perry Melbourne Australia
>
>
>
>  
>