The diodes in the original version have been removed, because they served no meaningful purpose and an R2R ladder design was used for the DA conversion. This not only improves the linearity of the DAC greatly, but it also ensures that the output impedance remains stable and of course means not having to buy 8 or 9 different non-standard value resistors. Pin 14 has also been chosen as ground instead of pin 9 to make it compatible with printer ports that have been converted to 8-Bit. The completed devices look like this: