Can someone tell me why the output amplifiers from the DAC needs a +/-12V supply? I always thought the line out was less than this.
The 1937 itself does not need the 12V bipolar supplies but the external Op-Amps on the evaluation board does. This is because the DAC will output 4.96V differentially. Each pin will swing approximately 2.49V peak to peak when using 3.3V AVDD power supply to the part. So when you measure across the two differential output pins you will be seeing a 4.96V peak to peak signal. I suppose you could use a single ended 5V op-amp that goes rail to rail but that would be asking a lot of the Op-Amp. So the next best thing is to run it differentially at 12V so that you can have some gain and still have headroom. Plus, this was an evaluation board so we wanted it to sound good.
This board was designed a little while back. Now we just put a passive filters on the eval boards and leave it up to the users to amplify it for their needs. You do not have to implement the DAC filter and amplifiers like we did. It is just a suggestion.
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