Originally Posted by nick_charles
But for some tests I used the Line out on the DACs that have a built-in amp and sent the signal to a separate amp with the same result, the external amp is an M^3 , one of the DACs has no built-in amp so always used the M^3, of course the M^3 could be equally flawed
It is possible all three DACs are equally crappy but I hesitate to get another (more expensive) one and find the same problem
LOL! Maybe the amps are not that flawed. AFAIK audio amps should work well in the audio range (< 20 kHz). Asking an audio amp to be uber-ultra-mega-linear while playing stuff loud in the ultrasonic range for the house pets might be unnecessarily a bit too much.
Looking at the datasheet for the AD1852 (what I think the Zero DAC uses) it seems it uses a 3rd order Bessel with corner frequency at 75 kHz:
I dunno, but IMO 75 kHz seems a bit too much.
Furthermore, judging from the plots in the link below (not sure about their accuracy), it seems some delta sigma DACs may put out quite a bit of stuff in the ultrasonic range which may also indicate to high a corner frequency in the output low pass filter, or it's absence, perhaps requiring further filtering before signal hits the amp:
Lowering the BW of the analog low pass filter (or adding one) prior to the amp might improve things out. Or perhaps the Amps could add an input analog low pass filter.
Edited by ultrabike - 12/10/13 at 9:19pm