Page 1
m Pure Class A operation delivers quality power: 30 watts × 2 into 8 ohms m Power
MOS-FET output stage features 3-parallel push-pull confi guration m Input section
confi gured as instrumentation amplifi er m Further improved MCS+ circuit in amplifi er
section m Current feedback topology combines stable operation with outstanding
sound m Bridged mode allows upgrading to monophonic amplifi er m Strong power
supply with large power transformer and ample fi ltering capacity m 4-step gain control
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Pure Class A sound that’s every audiophile’s dream — Input stage features fully balanced signal paths as found in high-quality instrumentation amplifi ers.
Further refi ned MCS+ topology and current feedback result in superb sound
quality and outstanding S/N ratio and other performance parameters. Strong
power supply section and power MOS-FET devices in triple-parallel pushpull confi guration sustain linear power output progression down to ultra-low
impedances, with the capability to deliver 150 watts into 1 ohm (music signal).
A pure class A amplifi er maintains a constant current fl ow
regardless of the presence or absence of a musical signal. This makes it possible to create a perfectly stable
sound stage with unparalleled ambience that is the dream
of any audiophile. Within this rarefi ed breed of amplifi ers,
the high-end pure class A stereo amplifi er A-65 has gar-
nered praise the world over as the ultimate reference for
superb performance and sheer sonic excellence. The A-35
was developed as a successor to the A-30 while inheriting many design aspects of the A-65. Dedication to the
best sound possible is always an Accuphase hallmark.
The use of the instrumentation amplifi er principle allows
fully balanced input signal paths, and further refi ned MCS+
topology pushes noise and distortion down to absolutely
minimal levels. In terms of its design as well as its sound,
the A-35 offers a highly attractive entry point to the world
of pure class A.
In the output stage of the A-35, proven power MOS-FET
devices are used in a triple-parallel confi guration for each
channel. MOS-FETs have excellent frequency characteristics, and their high input impedance reduces the load
imposed on the preceding drive stage. The devices are
directly mounted on large heat sinks for effi cient dissipa-
tion of thermal energy, assuring perfect operation stability. Driving these devices in pure class A produces rich,
high-defi nition sound that brings out the fi nest nuances in
the music.
The power supply of an amplifi er is its ultimate source of
energy. Unless it provides ample reserves, sound quality
will suffer, and even basic performance parameters may
not be met. The A-35 has a massive power transformer
and two 47,000 μF smoothing capacitors specially selected for their sonic properties. This sustains an output power
rating of 120 watts into 2 ohms, 60 watts into 4 ohms, or
30 watts into 8 ohms per channel, and it enables the A-35
to perfectly handle even very-low impedance speakers or
speakers with wildly fl uctuating impedance characteristics.
To prevent clipping on occasional momentary high-level
pulses, the maximum clipping level of the A-35 is set to 50
watts per channel into 8 ohms (sine wave output). Use in
bridged mode is also possible, turning the A-35 into a highpower monophonic amplifi er.
n Triple push-pull arrangement of power MOS-FETs delivers 150 watts per
channel into 1 ohm (music signals), 120 watts into 2 ohms, 60 watts into
4 ohms, or 30 watts into 8 ohms.
n Strong power supply with large transformer and high fi ltering capacity.
The power supply features a large high-effi ciency transformer and two 47,000 μF
aluminum electrolytic capacitors selected for sound quality.
n
Instrumentation amplifi er principle allows fully balanced signal paths, and
current feedback amplifi er topology drastically improves S/N ratio.
n Bridged mode supports upgrading to monophonic amplifi er with 300
watts into 2 ohms (music signals), 240 watts into 4 ohms, or 120 watts
into 8 ohms.
Simply by setting the mode selector to the bridged position, the A-35 is turned into a
monophonic amplifi er with 4 times the output power as compared to stereo operation.
This can be used when more power reserves are needed.
n Redesigned NFB circuit path results in minimized output
impedance, thereby further improving the damping factor.
This manifests itself in even better sound quality.
n Analog power meters with off/sensitivity selector.
Meter illumination and operation as well as meter sensitivity (0 dB,
–20 dB) can be controlled with a selector.
Meter selector
n 4-step gain control also minimizes residual noise.
The gain control switches gain in the fi rst instrumentation amplifi er
stage. Four settings are available: MAX, –3 dB, –6 dB, –12 dB.
n Fully balanced input stage shuts out external noise
interference.
n
Mode selector with dual mono position supports bi-amping.
n Oversize speaker terminals accept also Y lugs.
Large speaker terminalsHigh-reliability parts selected for sound quality
Protection and power meter circuit assembly
Unbalanced and balanced input connectors
Power transformer
Filtering capacitors
Gain selector
Instrumentation amplifi er
INPUT
NFB
NETWORK
GAIN CONTROL
CIRCUIT
NFB
NETWORK
INPUT
Gain control
Figure 1 Circuit diagram of amplifi er section (one channel)
Bias
stabilizer
Bias
stabilizer
Bias
stabilizer
Bias
stabilizer
MCS+ (MultipleCircuit Summing)
REGULATOR
Bias
stabilizer
REGULATOR
NFB
NETWORK
NFB
NETWORK
SPEAKER
TERMINALS
OUTPUT
3-parallel push-pull
power MOS-FETs
Output current (A)
Output voltage (V)
1-ohm operation possible
Figure 2 Load impedance vs. output power
with music signals only
(output voltage/output current)
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Instrumentation amplifi er and
further refi ned MCS+ topology
Instrumentation amp confi guration allows
fully balanced signal paths
The newly adopted “instrumentation amplifi er”
principle 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
signifi cant advantage is the fact that external noise
and other external infl uences are virtually shut
out. The result is a power amplifi er with drastically
improved operation stability and reliability.
Signal input stage Power amplifi er stage
INPUT
NFB
NETWORK
GAIN CONTROL
CIRCUIT
NFB
NETWORK
INPUT
Instrumentation amplifi er confi guration
OUTPUT
n
Power amplifi er assembly
Power amplifi er assembly with
three parallel push-pull power MOS-FET
pairs per channel mounted directly to large heat
sink, MCS+ circuitry, and current feedback amplifi er.
Further refined MCS+ topology reduces
noise even further
Accuphase’s original MCS (Multiple Circuit
Summing) principle uses a number of identical
circuits connected in parallel to achieve superior
performance characteristics. MCS+ is a further
refi ned version of this approach. By extending
parallel operation to the class A drive stage of
the current/voltage converter, the noise fl oor has
been further lowered.
Current feedback principle assures excellent
phase characteristics in high range
As shown in the illustration, the A-35 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.
INPUT
INPUT
Buffer
Buffer
Current
adder
Principle of current feedback amplifi er
I/V
converter
Trans-impedance amplifi er
Current NFB
network
Amp-
lifi er
OUTPUT
Page 4
Using two A-35 units, bridged connection or bi-amping is possible. n Input signal to be connected to LEFT connector (BALANCED or UNBALANCED) on both units.
n
Left loudspeaker
Connection example for bridged setup
Right loudspeaker
In bridged mode, the A-35 becomes a monophonic
amplifi er with even higher power output.
✽ speaker terminals of A-35 are not used.
LOW HIGH LOW HIGH
RIGHT LEFT RIGHT LEFT
Connection example for bi-amping setup
Right loudspeakerLeft loudspeaker
In a bi-amped setup, the speaker units for the LOW
frequency range and HIGH frequency range are driven
by separate amplifi ers for optimum sound quality.
✽ The speakers must have a built-in crossover network
and separate inputs for LOW and HIGH range.
A-35 for
left channel
Preamplifi er
Front Panel
n
Rear Panel
n
A Input type indicator
UNBALANCED, BALANCED
B Left/Right-channel output power meters
(indication in dB and %)
C Bridge mode indicator
D Meter selector
OFF, 0 dB, –20 dB
E Power switch
F Input selector button
UNBALANCED, BALANCED
G
Gain selector
–
3 dB, –6 dB, –12 dB
MAX,
A-35 for
right channel
Mode selector of A-35
set to BRIDGE on
both units
H Unbalanced inputs
I Balanced inputs
a Ground b Inverted (–)
c Non-inverted (
J Mode selector
)
+
DUAL MONO, NORMAL, BRIDGE
K Left/Right-channel speaker output
terminals
L AC power supply connector
A-35 for
left channel
Mode selector of A-35
Preamplifi er
set to DUAL MONO on
both units
GUARANTEED SPECIFICATIONS
[Based on the EIA RS-490 test standard]
m Rated Continuous Average Output Power (at 20–20,000 Hz)
Stereo use 150 W/ch 1-ohm load ()
(both channels operating 120 W/ch 2-ohm load
simultaneously) 60 W/ch 4-ohm load
30 W/ch 8-ohm load
Monophonic use 300 W 2-ohm load ()
(Bridge connection) 240 W 4-ohm load
120 W 8-ohm load
m Total Harmonic Distortion
Stereo use 0.05% 2-ohm load
(both channels operating 0.03% 4 to 16-ohm load
simultaneously)
Monophonic use 0.05% 4 to 16-ohm load
(Bridge connection)
m IM Distortion 0.01%
m Frequency Characteristics At rated continuous average output:
20 - 20,000 Hz
At 1 W output: 0.5 - 160,000 Hz
m Gain
(Same for both stereo and monophonic use)
m GAIN Switch Settings MAX, –3 dB, –6 dB, –12 dB
m Load Impedance Stereo use: 2 to 16 ohms
Monophonic use: 4 to 16 ohms
m Damping Factor 200
m Input Sensitivity (at 8-ohm load, with GAIN switch set to MAX)
Stereo use 0.57 V at rated continuous average output (30 W)
0.11 V at 1 W output
Monophonic use 1.14 V at rated continuous average output (120 W)
0.11 V at 1 W output
m Input Impedance Balanced: 40 kilohms Unbalanced: 20 kilohms
m S/N (A-weighted) 111 dB when GAIN switch set to MAX
118 dB when GAIN switch set to –12 dB
(At rated continuous average output)
m Output Meters
m Power Source AC 120 V/230 V, 50/60 Hz
(Voltage as indicated on rear panel)
m Power Consumption 155 W (with no input)
270 W in accordance with IEC 60065
m Maximum External Dimensions
Width 465 mm (18 5/16")
Height 170 mm (6 11/16")
Depth 425 mm (16 3/4")
m Mass 22.8 kg (50.3 lbs) net
29.0 kg (64.0 lbs) in shipping carton
Note: Load ratings marked () apply only to operation with music signals.
0, –0.2 dB
+
0, –3.0 dB
+
28.0 dB (when GAIN switch set to MAX)
For music signals only: 1-ohm (for stereo) and 2-ohm (mono)
loads are also supported.
Logarithmic compression type; illumination turn-off capability;
meter sensitivity switch (–20 dB);
3 dB (indication in both dB and %)
–40 to
+
A-35 for
right channel
Remarks
This product is available in versions for 120/230 V AC. Make sure that the voltage shown on the rear panel matches the AC line voltage in your area.
The shape of the AC inlet and plug of the supplied power cord depends on the voltage rating and destination country.
Supplied accessory
● AC power cord
m
Specifi cations and design subject to change without notice for improvements.
http://www.accuphase.com
F0905Y PRINTED IN JAPAN 851-0186-00 (AD1)
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