Sony STR-DA1000ES Technical Background page 25

Toroidal Power Supply (STR-DA9000ES)
Like the STR-DA2000ES, DA3000ES and DA5000ES, the top-of-the-line
DA9000ES operates the S-Master Pro amplifier from a two-stage power supply.
And like these other receivers, in the DA9000ES, the second stage is an analog,
constant voltage supply. But where the other receivers use a Pulse Power
Supply, the DA9000ES uses an analog supply with a giant toroidal core power
transformer. Sony made this choice for strictly practical reasons: we could not
build a pulse power supply with the current capability for 200 watts per channel,
for 7 simultaneous channels into 8 ohms (20—20,000 Hz, 0.15% THD).
For this reason, the first stage of STR-DA9000ES power supply wields an
extremely massive toroidal-core power transformer. In fact, the unusual height of
the DA9000ES chassis is determined in part by the size of the power
transformer. Thanks to this transformer, the current delivery of the DA9000ES is
an incredible 12 amps per channel. This is more than enough current to drive
"difficult," low-impedance loudspeakers, including models rated at 4 ohms with
impedance dips down to 2 ohms!
Power transformer cores and windings can vibrate and degrade the
sound, radiating 60 Hz hum into nearby audio circuits. That's why Sony chose
the toroidal core design, which enables the transformer windings to be wrapped
without the voids or gaps that permit vibration. This results in far less radiation,
far less radiated hum.
The extraordinary size and weight of the STR-DA9000ES receiver is
explained in part by the size and weight of this toroidal-core power
transformer.
ES Receivers V3.0 Page 25