I've been dealing with LF noise on my latest DAC design for a while. It turns out that measuring LF noise is not so easy, there is so much floating around in the environment its tough to separate external noise from device noise.
I finally wound building a very low noise amplifier powered by batteries in a small metal box with shielded cable going to the spectrum analyzer and shielded test lead for the DUT. With this I could reliably measure the LF noise at various points inside the DAC circuit. I eventually tracked it down to the very low noise discrete regulator I was using, the voltage setting network was picking up 60Hz rediated from the power transformer and feeding that to the output stage. I fixed it by separately shielding the regulator, this cut the 60Hz on the output from -60 to -115db, pretty decent for a bit of shielding! So with that I'm down to -121db noise floor with -115db spike at 60HZ and and -118db at 120Hz. Not too bad. I'll have to try the ADM test with this. Its not going to be really great, this is a zero feedback class a output stage which does have some distortion products. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=72147 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
