supplement AW: less hum: switching power supply?

[Haible Juergen]

I have recently quotet the Quantec QRS as an example for High End 
performance *despite* a switching power supply for the analogue part.
Meanwhile, I've investigated a little further. The switcher frequency
is hard locked to the ADC's sample frequency (20kHz), and the
anti aliasing filter to prevent interaction with this frequency is a 16-
or 17-pole LPF, go figure that.
So, under these circumstances, it can hardly count as a general example
for a switcher not being harmful.

JH.