SV: Re: [sdiy] R2R ladder with feedback loop?

[harry bissell]

ROTF...

yes... you become an "S-DIY" master by solving problems !!!

otoh... you will not become a master until you learn to
'choose your fights' carefully.  It might be that the best
solution for a DAC is uh... a DAC. And there are free
samples available from many manufacturers. In many cases
they will sample you even if you are a student or individual
(call yourself a 'consultant' :^)

You don't get extra points for making your synth from an
Apollo-13 bag of parts (you are ~not~ stranded in space..
are you ???  ;^).  If you are an *audiophile* (see also
necro, pedo...) you might get some credit for using all vacuum
tubes...

Scott Gravenhorst of course gave the obvious answer, lower
the reference voltage until the current is low enough.

Also note that for a simple 7 bit ladder... Sequential Circuits
needed to parallel buffers to drive the most significant bits.
They matched resistors (in quantity) to .1%  (ouch)

Bet they were thrilled when the "age of the monolythic dac"
arrived  :^P

Good Luck !

H^) harry


Karl Ekdahl wrote:
> Thanks all for your answers.
>
> I realized that i'd get both the "buy a DAC" and "get
> other resistors" answers - and of course your right,
> but as usual i'd like to use what i have. This both
> because i don't want to spend any money (at all) and
> beause i like the challange - hey, how i'm going to be
> a SDIY master without solving problems?
>
> So, i'm probably still going to try and find a way. I
> was thinking wheter i could utilize the op amp
> configuration often used in resistor string keyboards
> somehow.
>
> Oh yes, this is for a CV quantizer btw.
>
> Karl
>
>
>
>
> --- John Luciani <jluciani at gmail.com> skrev:
>
>   
>> On 8/19/06, Karl Ekdahl <elektrodwarf at yahoo.se>
>> wrote:
>>
>>     
>>> Hi list,
>>>
>>> I want to throw together a simple R2R ladder using
>>>       
>> 1%
>>     
>>> 100 ohm resistors, the problem is that a standard
>>> configuration would draw way too much current. I
>>>       
>> was
>>     
>>> thinking that there has to be some neat little
>>>       
>> op-amp
>>     
>>> feedback trick that can overcome this problem but
>>> can't think of it myself.
>>>       
>> Multiplying DACs usually contain just the R2R
>> ladder. Checkout ADI and Maxim.
>>
>> ADI had a multiplying DAC handbook which may give
>> you some additional
>> ideas.
>>
>> (* jcl *)
>>
>>
>> -- 
>> http://www.luciani.org
>>
>>     
>
>
>
>