I think i have solved the thing, a trace from the ladder directly to a power amplifier LM386 which i used in the first days to drive a square signal generated by the pic... When i removed this the values are quite good, at least very close to what should they be. For a FF i get about 4.7v which is not bad... I guess this is the last time i am using a perf board to do any serious learning stuff although i learned something from my mistake. On my scope the PCM soundwave is clearly seen as i see it inside my Audacity wave editor on the computer. Now in order to hear something on a small speaker i will need an amplifier :) I was thinking about using a LM358 opamp since the ~5v VCC is all the voltage i have. Do you think this will be enough or i will also need a power amplifier like lm386 ? On Jan 24, 2008 10:54 PM, Dave Tweed wrote: > Vasile Surducan wrote: > > Hand made R-2R ladder is the worst option ever for a DAC. > > Not necessarily ... > > > I hope you have read first the theory of R-2R D2A and the non linearities > > you may get because of resistor unmatch. > > I'm with you so far ... although you can do pretty well with, say, 25 1% > resistors of all the same value (from the same batch, if possible) to build > an 8-bit converter. > > > Also the inequal output impedance with bit variation... > > Nope, dead wrong on that one. Assuming the bit drivers have negligiple > resistance compared to R, The output impedance of an R-2R network is > constant, and it's R! See the following link for details: > > http://www.dtweed.com/circuitcellar/caj00100.htm#1532 > > The PDF link works, but the HTML version has gone missing. The relevant > text is on page 2, with diagrams on page 3. > > -- Dave Tweed > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist