Jeff Rowland uses SMPS for low noise. That’s why he uses them in applications where efficiency is non-issue, like Capri preamp. SMPS got bad rap from crude computer applications but when is done right is extremely quiet. Most of linear power supplies are in reality primitive switchers that switch at 120Hz at the peak of the voltage causing transition noise that propagates thru the amplifier. In addition 120Hz ripple is difficult to filter out thus requiring big electrolytic caps. These cap, in series with the signal path (circuit closes thru them), are inductive and slow down response. Power transformer has to be huge at this low frequency. Modern SMPS switches at zero voltage/ zero current at frequency that is inaudible and easy to filter out (Rowland’s 625 SMPS switches at 1MHz). It has fast response time and is line and load regulated while linear supply in power amps is not. Huge transformer is replaced by small ferrite one that can carry the same power at very high frequency.
Benchmark replaced linear supply in their newer DACs with switcher while their new 132dB S/N ABH2 amplifier also has SMPS. SMPS can be quiet not only electrically but also acoustically being free of buzz and with AC/DC operation, often in wide range.
http://jeffrowlandgroup.com/kb/questions.php?questionid=145
Benchmark replaced linear supply in their newer DACs with switcher while their new 132dB S/N ABH2 amplifier also has SMPS. SMPS can be quiet not only electrically but also acoustically being free of buzz and with AC/DC operation, often in wide range.
http://jeffrowlandgroup.com/kb/questions.php?questionid=145