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Extracted text from Accuphase A 46 Brochure (Ocr-read)
Page 1
Trans-impedance amplifier
Amplifier Output (+) input bufferCurrent adder
(-) input buffer
Current NFB network
/V NFB
NETWORK
NFB
NETWORK
NFB
NETWORK
OUTPUT
´ INPUT
µ INPUT
Signal input stage Power amplifier stage
´µ
´µ
´µ
Instrumentation amplifier
OUTPUT
Bias stabilizer
circuit
-“INPUT
+INPUT
NFB
NETWORK
NFB
NETWORK
GAIN CONTROL CIRCUIT
+
-“
-“
+
REGULATOR
REGULATOR
+ B1
-“ B1
-“ B2
+ B2
Q1
Q3
Q2
Q4 Q8
Q6
Q7
Q5 Q9
Q17 Q19
Q18 Q20
Q21
Q22
Q23 Q25 Q27 Q29
Q24 Q26 Q28 Q30
Q31
Q32
Q13
Q1 1 Q15
Q10 Q14
Q12 Q16
NFB
NETWORK
Bias stabilizer
circuit
Bias stabilizer
circuit Bias stabilizer
circuit
Bias stabilizer
circuit
Gain control MCS+ (Multiple Circuit Summing)
Power MOS-FETs
6-parallel push-pull
Output current (A)
Output voltage (V)
Ã’ 1-ohm operation possible
with music signals only
converter
Principle of current feedback amplifier Instrumentation amplifier configuration
Ù
Figure 1 Circuit diagram of amplifier section (one channel)
Parts selected for sound quality and reliability Meter circuitry assembly Power MOS-FETs
Filtering capacitors
Toroidal power transformer
Line/balanced input connectors
Large speaker terminals Gain selector
Meter selector
MOS-FET switches Input selector
Protection circuitry
Figure 2 Load impedance vs. output power
(output voltage/output current)
Power amplifier assembly with six parallel push-pull
power MOS-FET pairs per channel mounted directly to
large heat sink, MCS+ circuitry, and current feedback
amplifier.
Instrumentation amplifier and further refined MCS+ topology
Phase selector for balanced input
Ã-
Ã-
Pure Class A power amplifier with power M\fS-F\bT devices -“ Fully balanced signal paths
realized through instrumentation amplifier configuration. Further refined MCS+ topology
and current feedback result in superb sound quality and excellent ratings for S/N ratio,
THD, and other parameters. Strong power supply and power M\fS-F\bT devices in
six-parallel push-pull configuration sustain an amazing 360 watts per channel into ultra-low
impedance 1-ohm loads (with music signals). 4-step gain control provides flexibility.
Pure Class A power amplifiers from Accuphase
have long been blending the purity of class A
operation with the superior performance of
power MOS-FETs. Acclaimed by audiophiles
the world over, these products reflect a level of
technical know-how that is second to none.
Each model in the A-65/A-45/A-35 lineup has
received high praise, both for sound quality and
performance. The A-46 is a minor-change
successor to the A-45, positioned as the
medium power level model of the series.
Naturally, the A-46 also demonstrates the same
unwavering dedication to sound quality and
outstanding design policy which are the
hallmark of Accuphase. This pure class A stereo
power amplifier with its distinctive external heat
sinks is built for the true enjoyment of music.
The A-46 uses latest instrumentation amplifier
topology throughout, which allows fully balanced
transmission in all signal handling stages. The
power amplifier section features further
improved MCS+ topology and the renowned
current feedback approach. This results in
electrical characteristics that surpass even the
demanding standards set by its predecessors.
Employing only highest grade materials and
strictly selected parts, the A-46 realizes very low
output impedance which ensures that constant
drive voltage is available for the speakers.
The output stage features power MOS-FETs
renowned for their excellent sound and superior
reliability. For each channel, six of these devices
are arranged in a parallel push-pull class A
arrangement. MOS-FETs have excellent frequency
response characteristics and high input impedance,
which reduces the load of the preceding (drive)
stage. Driving these devices in pure class A means
that constant power is always supplied, regardless
of the presence or absence of a musical signal.
This makes the amplifier completely immune to
external influences and ensures stable operation at
all times. The large heat sinks mounted on the
outside reliably prevent internal heat buildup,
allowing the amplifier to sustain output levels of as
much as 360 watts per channel into 1 ohm (with
music signals). If even higher power is required,
bridged mode turns the A-46 into a high-grade
monophonic power amplifier.
Ù Power modules with 6-parallel push-pull arrangement of power
MOS-FETs deliver a guaranteed linear output of 360 watts per
channel into 1 ohm (music signals only), 180 watts into 2 ohms, 90
watts into 4 ohms, or 45 watts into 8 ohms.
Ù Amply dimensioned power supply with high-efficiency toroidal
transformer and two large 47,000 µF filtering capacitors.
Ù Bridged mode allows upgrading to monophonic amplifier
with 720 watts into 2 ohms (music signals only), 360 watts
into 4 ohms, or 180 watts into 8 ohms.
Ù Revised NFB design minimizes output impedance and
increases damping factor, resulting in further improved
sound quality.
Ù Fully balanced input stage shuts out external noise
interference.
Ù Mode selector for easy switching between dual
mono/stereo/bridged operation
Ù Front panel input type selector (line/balanced).
Ù 4-step gain control (MAX, -3 dB, -6 dB, -12 dB) minimizes
residual noise.
Ù
Large analog power meters with operation/illumination and sensitivity selector.
Ù Speaker protection uses semiconductor (MOS-FET)
switch. Elimination of mechanical switches assures
long-term reliability and improved signal purity,
resulting in further improved sound quality.
Ù PCB copper foil and all
major signal path
components are gold-
plated.
Ù Two sets of speaker
outputs, with large
terminals that accept also
Y lugs.
Instrumentation amp configuration allows
fully balanced signal paths
The advanced instrumentation amplifier
principle used in the A-46 ensures that all
signal paths from the inputs to the power amp
stage are fully balanced. This results in
excellent CMRR (common mode rejection
ratio) and minimal distortion. Another
significant advantage is that external noise
and other external influences are virtually shut
out. The result is a drastic improvement in
operation stability and reliability. Further refined MCS+ topology for even
lower noise
Accuphase's original MCS (Multiple Circuit
Summing) configuration uses a number of
identical circuits connected in parallel to achieve
superior performance characteristics. MCS+ is
a further refined version of this approach. By
extending parallel operation to the class-A drive
stage of the current/voltage converter, the noise
floor has been lowered further. Current feedback principle assures excellent
phase characteristics in high range
As shown in the illustration, the A-46 uses the
output signal current rather than voltage for
feedback. Since the impedance at the current
feedback point is very low, there is almost no
phase shift. A minimal amount of NFB
therefore results in maximum improvement of
circuit parameters.
In the factory default
condition, the switch is
set to the left side ("pin
e +"), as shown in the
illustration.
If the balanced output
of the connected
preamplifier has a "pin
w
+" arrangement, the
switch should be set to
the right side.
Page 2
Trans-impedance amplifier
Amplifier Output (+) input bufferCurrent adder
(-) input buffer
Current NFB network
/V NFB
NETWORK
NFB
NETWORK
NFB
NETWORK
OUTPUT
´ INPUT
µ INPUT
Signal input stage Power amplifier stage
´µ
´µ
´µ
Instrumentation amplifier
OUTPUT
Bias stabilizer
circuit
-“INPUT
+INPUT
NFB
NETWORK
NFB
NETWORK
GAIN CONTROL CIRCUIT
+
-“
-“
+
REGULATOR
REGULATOR + B1
-“ B1
-“ B2
+ B2
Q1
Q3
Q2
Q4 Q8
Q6
Q7
Q5 Q9
Q17 Q19
Q18 Q20
Q21
Q22
Q23 Q25 Q27 Q29
Q24 Q26 Q28 Q30
Q31
Q32
Q13
Q1 1 Q15
Q10 Q14
Q12 Q16
NFB
NETWORK
Bias stabilizer
circuit
Bias stabilizer
circuit Bias stabilizer
circuit
Bias stabilizer
circuit
Gain control MCS+ (Multiple Circuit Summing)
Power MOS-FETs
6-parallel push-pull
Output current (A)
Output voltage (V)
Ã’ 1-ohm operation possible
with music signals only
converter
Principle of current feedback amplifier Instrumentation amplifier configuration
Ù
Figure 1 Circuit diagram of amplifier section (one channel)
Parts selected for sound quality and reliability Meter circuitry assembly Power MOS-FETs
Filtering capacitors
Toroidal power transformer
Line/balanced input connectors
Large speaker terminals Gain selector
Meter selector
MOS-FET switches Input selector
Protection circuitry
Figure 2 Load impedance vs. output power
(output voltage/output current)
Power amplifier assembly with six parallel push-pull
power MOS-FET pairs per channel mounted directly to
large heat sink, MCS+ circuitry, and current feedback
amplifier.
Instrumentation amplifier and further refined MCS+ topology
Phase selector for balanced input
Ã-
Ã-
Pure Class A power amplifier with power M\fS-F\bT devices -“ Fully balanced signal paths
realized through instrumentation amplifier configuration. Further refined MCS+ topology
and current feedback result in superb sound quality and excellent ratings for S/N ratio,
THD, and other parameters. Strong power supply and power M\fS-F\bT devices in
six-parallel push-pull configuration sustain an amazing 360 watts per channel into ultra-low
impedance 1-ohm loads (with music signals). 4-step gain control provides flexibility.
Pure Class A power amplifiers from Accuphase
have long been blending the purity of class A
operation with the superior performance of
power MOS-FETs. Acclaimed by audiophiles
the world over, these products reflect a level of
technical know-how that is second to none.
Each model in the A-65/A-45/A-35 lineup has
received high praise, both for sound quality and
performance. The A-46 is a minor-change
successor to the A-45, positioned as the
medium power level model of the series.
Naturally, the A-46 also demonstrates the same
unwavering dedication to sound quality and
outstanding design policy which are the
hallmark of Accuphase. This pure class A stereo
power amplifier with its distinctive external heat
sinks is built for the true enjoyment of music.
The A-46 uses latest instrumentation amplifier
topology throughout, which allows fully balanced
transmission in all signal handling stages. The
power amplifier section features further
improved MCS+ topology and the renowned
current feedback approach. This results in
electrical characteristics that surpass even the
demanding standards set by its predecessors.
Employing only highest grade materials and
strictly selected parts, the A-46 realizes very low
output impedance which ensures that constant
drive voltage is available for the speakers.
The output stage features power MOS-FETs
renowned for their excellent sound and superior
reliability. For each channel, six of these devices
are arranged in a parallel push-pull class A
arrangement. MOS-FETs have excellent frequency
response characteristics and high input impedance,
which reduces the load of the preceding (drive)
stage. Driving these devices in pure class A means
that constant power is always supplied, regardless
of the presence or absence of a musical signal.
This makes the amplifier completely immune to
external influences and ensures stable operation at
all times. The large heat sinks mounted on the
outside reliably prevent internal heat buildup,
allowing the amplifier to sustain output levels of as
much as 360 watts per channel into 1 ohm (with
music signals). If even higher power is required,
bridged mode turns the A-46 into a high-grade
monophonic power amplifier.
Ù Power modules with 6-parallel push-pull arrangement of power
MOS-FETs deliver a guaranteed linear output of 360 watts per
channel into 1 ohm (music signals only), 180 watts into 2 ohms, 90
watts into 4 ohms, or 45 watts into 8 ohms.
Ù Amply dimensioned power supply with high-efficiency toroidal
transformer and two large 47,000 µF filtering capacitors.
Ù Bridged mode allows upgrading to monophonic amplifier
with 720 watts into 2 ohms (music signals only), 360 watts
into 4 ohms, or 180 watts into 8 ohms.
Ù Revised NFB design minimizes output impedance and
increases damping factor, resulting in further improved
sound quality.
Ù Fully balanced input stage shuts out external noise
interference.
Ù Mode selector for easy switching between dual
mono/stereo/bridged operation
Ù Front panel input type selector (line/balanced).
Ù 4-step gain control (MAX, -3 dB, -6 dB, -12 dB) minimizes
residual noise.
Ù
Large analog power meters with operation/illumination and sensitivity selector.
Ù Speaker protection uses semiconductor (MOS-FET)
switch. Elimination of mechanical switches assures
long-term reliability and improved signal purity,
resulting in further improved sound quality.
Ù PCB copper foil and all
major signal path
components are gold-
plated.
Ù Two sets of speaker
outputs, with large
terminals that accept also
Y lugs.
Instrumentation amp configuration allows
fully balanced signal paths
The advanced instrumentation amplifier
principle used in the A-46 ensures that all
signal paths from the inputs to the power amp
stage are fully balanced. This results in
excellent CMRR (common mode rejection
ratio) and minimal distortion. Another
significant advantage is that external noise
and other external influences are virtually shut
out. The result is a drastic improvement in
operation stability and reliability. Further refined MCS+ topology for even
lower noise
Accuphase's original MCS (Multiple Circuit
Summing) configuration uses a number of
identical circuits connected in parallel to achieve
superior performance characteristics. MCS+ is
a further refined version of this approach. By
extending parallel operation to the class-A drive
stage of the current/voltage converter, the noise
floor has been lowered further. Current feedback principle assures excellent
phase characteristics in high range
As shown in the illustration, the A-46 uses the
output signal current rather than voltage for
feedback. Since the impedance at the current
feedback point is very low, there is almost no
phase shift. A minimal amount of NFB
therefore results in maximum improvement of
circuit parameters.
In the factory default
condition, the switch is
set to the left side ("pin
e +"), as shown in the
illustration.
If the balanced output
of the connected
preamplifier has a "pin
w
+" arrangement, the
switch should be set to
the right side.