Accuphase A-35 Brochure
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
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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