Audio DAC noise (dsPIC33FJ64GP802)
I'm using the internal 16-bit audio DAC on the 28-pin PDIP version of the dsPIC33FJ64GP802, and I'm hearing quite a bit of audio-range white noise. It is not loud, but it is not within the 62 db SNR spec.
I am using the right channel only, and have it connected up to a differential amplifier, exactly as in section 33.8 of the dsPIC reference manual. To narrow down the problem, I have disabled as many peripherals as I can, and am driving 0's onto the DAC output. I have the DAC default value set to 0 also.
I don't think it is problem with the analog power supply or other parts of the board, because when I disable the (internal) DAC output amplifier the noise goes away. I've tried disabling the PLL, using external resonators, and tried a few different sample rates, without effect.
Otherwise the DAC is working okay.
Does anybody have experience with this DAC? Are there any settings that can improve performance, peripherals I should disable?