Differential TDA1543 based NOS DAC

[dsavitsk]

Something I have been tinkering with for a while. This is basically your everyday TDA1543 NOS DAC except I put an inverter on the data line which flips the output phase. By using one chip inverted, I ended up with a differential pair. In hindsight, an Xor splitter might work slightly better, but this does the job.

In order to drive some headphones or long cables, I used a differential mosfet pairs and transformer coupled the whole thing. Since both sides are biased up the same amount (accomplished by carefully matching the mosfets, and then adjusting Vref a tad), no DC flows across the transformer. I also breadboarded a version without the mosfets using higher impedance transformers (Lundahl LL1930's) and even used as step-up devices, it worked pretty well with short cables.

There is also an ASRC. With these chips, this only seems to work at 44.1KHz, so I am just using the recovered clock from the receiver chip into the ASRC as a bit of a jitter reducer. Trying it with and without the chip, it does seem to help.