Sony STR-DA7100ES Technical Background page 30

Sony's Optimum Preamplification (OP) circuit improves the signal-to-
noise ratio across a broad range of volume control settings. The latest
version of the OP design controls volume with twice the resolution of our
previous design—0.5 dB steps instead of 1 dB
In Sony's previous OP design, the volume control operated in precise 1 dB
steps. However Sony found during critical listening at high volume levels that
smaller steps are sometimes useful. That's why the STR-DA3100ES and
DA2100ES incorporate a refined OP Processing system that enables you to vary
the volume setting in precise, 0.5 dB steps!
Optimum Preamplification is made possible by Sony's proprietary
CXD9725 integrated circuit.
Analog amplifiers depend heavily on the power supply filter capacitors.
Because these devices filter out 60 Hz line frequency hum, they play a crucial
role in protecting sound quality. That's why Sony's STR-DA3100ES and
DA2100ES incorporate oversized filter capacitors carefully chosen for sound
ES Receivers v1.0
Oversized filter capacitors
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