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JVC M-7050 - Technical Description

JVC M-7050
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TECHNICAL
DESCRIPTION
Super
A
power
amplifier
A
big
problem
has
remained
unsolved
in
the
progress
regarding
amplifier
technology:
how
can
class-A
operation
be
made
compatible
with
high
power
efficiency?
The
class-A
operation
is
best
in
terms
of
low
distortion;
its
critical
drawback
is
such
that
its
power
loss
is
greater
than
the
available
output
power.
Because
of
this,
class-B
amplifiers
have
generally
been
applied
for
power
amplification
because
they
offer
both
acceptable
distortion
and
power
efficiency.
However,
as
long
as
class-B
amplifiers
are
employed,
the
occurrence
of
crossover
distor-
tion
and
switching
distortion
is
inevitable.
Although
the
improvements
of
circuit
elements
have
realized
fairly
good
class-B
amplifiers,
when
their
values
of
distortion
are
referred
to,
the
‘‘nature”
of
distortion
is
still
detrimental
to
the
re-
produced
sound
quality.
To
solve
this
problem
by
improving
circuit
technology,
JVC
has
developed
its
new
‘’Super-A”’
power
amplifier.
The
Super-A
power
amplifier
consists
of
a
voltage
amplifier
stage
whose
distortion
is
minimized
by
compensating
for
the
non-linearity
of
semiconductors,
and
aclass-A
power
amplifier
stage
which
includes
a
bias
circuit
for
raising
the
power
effi-
ciency
to
such
a
degree
as
is
comparable
to
that
of
a
class-B
amplifier.
JVC’s
Super-A
power
amplifier
offers
the
following
features:
1)
Power
efficiency
is
extremely
high
despite
the
class-A
operation,
greatly
reducing
power
loss
and
heat
generation
compared
with
conventional
class-A
amplifiers.
2)
Switching
distortion
inherent
in
class-B
operation
is
com-
pletely
eliminated;
it
is
perfectly
zero.
3)
AVecE
distortion
*1,
ACob
distortion
*2
and
A
Vpe
dis-
tortion
“3
are
all
extremely
low
because
of
the
unique
non-distortion
circuit
configuration.
“1
Distortion
caused
by
non-linear
variations
of
current
gain
B
due
to
variations
of
collector-emitter
voltage
VCE.
*2
Distortion
caused
by
non-linear
variations
of
amplifier
gain
which
are
caused
by
non-linear
variations
of
feedback
capacity
Cob
due
to
variations
of
collector-emitter
voltage
VCE.
*3
Distortion
caused
by
non-linear
variations
of
base-emitter
voltage
VBE
of
power
transistor.
Distortion
of
measurement
system
Distortion
of
‘“Super—A”
Fig.
1
Output
and
residual
distortion
waveforms
of
measur-
ing
instrument
Fig.2
Output
and
distortion
waveforms
of
Super-A
am-
plifier
Fig.
3
Output
and
distortion
waveforms
of
class-AB
ampli-
fier
Voltage
amplifier
stage
utilizing
‘‘Super-A”’
performance
to
the
utmost
Fig.
4
shows
operating
characteristics
of
a
common-emitter
transistor;
8
varies
as
VCE
varies,
resulting
in
A
Vce
distortion
as
described
above.
Fig.
5
shows
a
variation
of
the
feedback
capacity
Cop
in
re-
lation
to
VCE.
This
non-linear
variation
of
Cop
due
to
varia-
tions
of
VCE
causes
a
non-linear
variation
of
the
amplifier
gain,
leading
to
the
A
Cob
distortion
mentioned
above.
Fig.
6
shows
operating
characteristics
of
a
common-base
transistor.
What
is
noteworthy
about
this
type
of
operation
is
that,
though
its
current
gain
is
O
dB,
its
output
linearity
in
constant-
current
drive
is
fairly
good
since
a
scarcely
varies
with
varia-
tions
of
VcE
(a=
1)
as
shown
by
the
equal
distance
between
adjacent
base
current
curves.
An
example
of
the
cascode-connected
amplifier
circuit
is
shown
in
Fig.
7.
The
features
of
this
circuit
are
good
frequ-
ency
response
(because
of
no
mirror
effect
due
to
Cob)
and
high
output
impedance.
This
means
that
this
circuit
eliminates
distortion
by
effectively
combining
the
advantages
of
common-emitter
and
base-emitter
configurations.
The
driver
stage
of
the
Super-A
power
amplifier
employs
an
applied
circuit
of
this
kind
and
a
drastic
reduction
in
distoriton
is
the
result.
Fig.4
Output
characteristics
of
common-emitter
amplifier
Fig.5
Cop
characteristic
Fig.6
Output
characteristics
of
common-base
amplifier
Fig.
7
Cascode
amplifier
Distortion
of
‘‘class
AB”
f=10
kHz,
THD=0.0008%
Fig.
1.
f=10
kHz,
Output
power=100W/8
QO,
THD=0.0009%
Fig.
2.
9
f=10
kHz,
Output
power=100W/8
Q
THD=0.0022%
Fig.
3.

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