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Design Features
page 3© 2002-2004 bel canto design, Ltd. eVo User’s Guide 042104
• High efficiency Digital Power
Processing output stage for cool
operation
• Analog signals are processed at small
signal level, all large signal power is
generated using the switching output
stage
• 700 watts of continuous power
output capability in Balanced
Mono mode
• Optimized balanced and single-
ended input stage
• THD and IMD <0.05%
• Damping Factor >100
• High thermal stability in all stages
• Regulated, low noise supplies for all
analog stages
• Audio Grade decoupling capacitors
and resistors used throughout
• Soft clipping insures graceful over
load
• High efficiency ‘green’ amplification
• Comprehensive protection circuitry
outside the signal path
The Bel Canto Design eVo digital out-
put stage is of unique simplicity. The
output uses 2 N channel MOSFET
switches switching between the
power supply rails. These switches
turn on and off within 30 billionths of
a second and provide an onresis-
tance path to the supplies of a few
thousandths of an ohm. These
switches switch alternately between
the supplies at a rate over 600,000
cycles per second (600 kHz). When
no audio signal is present, the ratio
between the time at the positive sup-
ply and the negative is balanced to
provide no audio frequency output.
The switching stage is isolated from
the loudspeaker by a single LC filter
stage. This 80kHz second order filter
is used to reject high frequency ener-
gy and maintain linear phase
response.
Furthermore, the digital power
processor adds small levels of high
frequency dither to insure that an
inherently linear output stage charac-
teristic is maintained from very low
to very high output levels. The audio
frequency information modulates the
output stage by changing the time
relationship between the positive and
negative supply rails. The critical
timing information is controlled by
the digital power processor and the
effective switching frequency is
changed over a 200 kHz to 1500 kHz
range. This spreads the digital ener-
gy created by the amplifier over a
wide bandwidth, greatly reducing the
energy at any one frequency. This
permits using a simple LC filter to
remove the high frequency energy
and maintains excellent phase
response.
The eVo Digital Output Stage and Digital Power Processor