Sony STR-DA1000ES Technical Background page 13

The discrete output FETs of the STR-DA2000ES.
The Low Pass Filter is a crucial stage in any digital amplifier. The filter
must have a turnover frequency high enough for high-resolution audio, yet have
a cutoff characteristic steep enough to suppress high-frequency noise elements.
In this way, the filter has a major influence on sound quality. That's why the
engineers of Sony ES selected the filter parts carefully and methodically. Instead
of choosing less expensive cylinder-type coils, the ES engineers chose exotic
toroidal coils, optimized for sound. Customers will never see these toroidal coils,
but they will hear the benefits in clean, open, non-fatiguing music reproduction.
The toroidal coils of Sony's Low Pass Filters are more expensive. But
their contribution to sound is more than worth the price.
ES Receivers V3.0
Toroidal Low Pass Filter
Page 13