m Pure Class A operation delivers quality power: 45 watts × 2 into 8 ohms
m Power MOS-FET output stage features 6-parallel push-pull configurationm Instrumentation amplifier principle m Further improved MCS+ circuit
topology m Current feedback combines stable operation with outstanding
sound m Bridged mode allows upgrading to true monophonic amplifier m Large
high-efficiency toroidal transformer rated for 600 VA m 4-step gain control

Pure Class A power amplifier uses power MOS-FET devices to deliver 45watts per channel (8 ohms) – Fully balanced signal paths as found in highquality instrumentation amplifiers. Further refined MCS+ topology andcurrent feedback result in superb sound quality and excellent ratings for S/Nratio, THD, and other parameters. Strong power supply and power MOSFET devices in six-parallel push-pull configuration sustain an amazing 360
watts per channel into ultra-low impedance 1-ohm loads (with music signals).
Pure Class A power amplifiers from Accuphasehave long been blending the purity of class
A operation with the superior performance ofpower MOS-FETs. Acclaimed by audiophiles
the world over, these products reflect a levelof technical know-how that is second to none.
Completing the A series lineup, the A-45 is ideal
for systems that demand not quite the highpower levels of the A-60 but require more power
than the A-30 provides. The A-45 of course also
demonstrates the same unwavering dedication
to sound quality and outstanding design policy
which are the hallmark of Accuphase. This pureclass A stereo power amplifier with its distinctive
external heat sinks is built for the true enjoymentof music.
The so-called instrumentation amplifier principle
is used throughout. The signal handling stages
feature further improved MCS+ topology andthe 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, theA-45 realizes the two most important goals ofan amplifier: very low output impedance andconstant drive voltage.
The output stage features power MOS-FETs
renowned for their excellent sound and superior reliability. For each channel, six of thesedevices are arranged in a parallel push-pullarrangement. Because MOS-FETs havenegative thermal characteristics, there is nodanger of thermal “runaway” as exists withbipolar transistors. Operation remains totallystable even when the amplifier is running hot.
Driving these devices in pure class A assureshigh-definition sound that brings out the finest
nuances in the music.
The heavy-duty power supply features a massive power transformer rated for a maximumof 600 VA, plus two smoothing capacitors of
47,000 μF each. This easily sustains 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-45 into ahigh-grade monophonic power amplifier.

n Power modules with 6-parallel push-pull arrangement of power MOS-FETsdeliver 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.

n Amply dimensioned power supply with high-efficiency toroidaltransformer and large filtering capacity.
The high-efficiency toroidal transformer is rated for 600 VA, and the two extralarge 47,000 μF aluminum electrolytic capacitors were selected for best sonicperformance.

Toroidal power transformern 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.
Bridged connection increases the output by a factor of 4, creating dramatic power
reserves in a monophonic configuration.

n Four gain control settings minimize residual noise.

Filtering capacitors

The gain control switches gain in the first stage of the instrumentation amplifier.
Four settings are available (MAX, –3 dB, –6 dB, –12 dB).

n Fully balanced input stage shuts out external noise interference.
n Mode selector for easy switching between dual mono/stereo/bridgedoperation.

n PCB copper foil and all major signal path components are gold-plated.

Gain selectorn Large analog power meters with off switch and sensitivity selector.
n Oversize speaker terminals accept also Y lugs.
Meter and input buttons

Power MOS-FETs

Large speaker terminals

Balanced input connectors

Parts selected for sound quality and reliability

Gold-plated partsAssembly with meter and protection circuitry

Instrumentation amplifier
Bias stabilizer
circuit+ INPUT

Bias stabilizer
circuitOutput current (A)Bias stabilizer
circuit

Bias stabilizer
circuit– INPUT

Bias stabilizer
circuitGain control

MCS+ (Multiple Circuit Summing-up)

Fig. 1 Circuit diagram of amplifier section (one channel)

Output voltage (V)Power MOS-FETs
6-parallel push-pull

1-ohm operation possible with music signals only

Fig. 2 Load impedance vs. output power(output voltage/output current)Instrumentation amplifier and further refined MCS+ topology
Instrumentation amp configuration allows
fully balanced signal paths
The newly adopted “instrumentation amplifier”
principle ensures that all signal paths from theinputs to the power amp stage are fully balanced. This results in excellent CMRR (commonSignal input stage

Power amplifier stage+ INPUT– INPUT

Instrumentation amplifier configurationn Power amplifier assemblyPower amplifier assemblywith six parallel push-pull
power MOS-FET pairs perchannel mounted directly tolarge heat sink, MCS+ circuitry, and current feedbackamplifier.

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 evenlower noise
Accuphase’s original MCS (Multiple CircuitSumming) principle uses a number of identicalcircuits 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 ofthe 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-45 uses theoutput signal current rather than voltage for
feedback. Since the impedance at the current
feedback point is very low, there is almost nophase shift. A minimal amount of NFB therefore
results in maximum improvement of circuit
parameters.

– Input
Buffer+ Input
BufferCurrent
adder

I-V
converter

AmplifieTrans-impedance
amplifie
Current NFB
network

Principle of current feedback amplifierOutput

Connection example for bi-amping setup
Left loudspeaker

In a bi-amped setup, the speaker units for theLOW frequency range and HIGH frequency
range are driven by separate amplifiers, for
optimum sound quality.

Connection example for bridged setup

Right loudspeaker

Left loudspeaker

Right loudspeakerIn bridged mode, the A-45 becomes a monophonic amplifier with even higher power
output.
For stereo operation, two A-45 units are required.

The speakers must have a built-in crossover networkand separate inputs for LOW and HIGH range.
Two A-45 units are required.

A-45
for right
channelA-45
for leftchannelMode selectorof A-45 (DUAL
MONO position)

A-45
for leftchannelA-45
for right
channelm Use the LEFT (BALANCED
or UNBALANCED) input
connectors for both A-45
units.

m Use the LEFT (BALANCED
or UNBALANCED) input
connectors for both A-45
units.

Mode selector ofA-45 (BRIDGEposition)

Preamplifiern Front Panel

Preamplifier

GUARANTEED SPECIFICATIONS[Guaranteed specifications are measured according to EIA standard RS-490.]m Continuous Average Output Power (20–20,000 Hz)
Stereo operation360 watts per channel into 1 ohm( )(both channels driven)
180 watts per channel into 2 ohms
90 watts per channel into 4 ohms
45 watts per channel into 8 ohms
Monophonic operation(bridged connection)

720 watts into 2 ohms( )360 watts into 4 ohms
180 watts into 8 ohms

Note: Load ratings marked ( ) apply only to operation with music signals.
m Total Harmonic Distortion

Stereo operation (both channels driven)
0.05% with 2 ohm load
0.03% with 4 to 16 ohm load
Monophonic operation (bridged connection)
0.03% with 4 to 16 ohm loadn Rear Panelm Intermodulation Distortion

0.004%m Frequency Response

At rated output:
At 1 watt output:

m Gain28.0 dB (with GAIN selector at MAX)(in stereo and monophonic operation)

m Gain Selection

MAX, –3 dB, –6 dB, –12 dB

m Output Load impedance

Stereo operation:
2 to 16 ohms
Monophonic operation: 4 to 16 ohms

20 ~ 20,000 Hz +0,0.5 ~ 160,000 Hz +0,–0.2 dB–3.0 dB

With music signals only, 1-ohm loads are permissible forstereo operation and 2-ohm loads for monophonic operation.
m Damping Factor

200m Input Sensitivity (with 8-ohm load, GAIN selector in MAX position)
Stereo operation:
0.76 V for rated output
0.11 V for 1 watt output
Monophonic operation: 1.51 V for rated output
0.11 V for 1 watt output
m Input Impedance

Balanced: 40 kilohms

Unbalanced: 20 kilohms

m Signal-to-Noise Ratio (A-weighted, input shorted)
115 dB (GAIN selector in MAX position)
120 dB (GAIN selector in –12 dB position)
At rated output
Left/right channel output power meters(dB and % scale)
Function indicators
METER –20 dB, UNBALANCED, BALANCED, BRIDGE
Meter operation/illumination button ON OFF
Meter sensitivity selector button (–20 dB)
Input selector button UNBALANCED BALANCEDPower switch
Gain selector
MAX –3 dB –6 dB –12 dB

Unbalanced inputs
Balanced inputs
 Ground Inverted (–)
 Non-inverted (+)
Left/right channel speaker output terminals
Mode selector
DUAL MONO NORMAL BRIDGEAC power supply connectorm Output Level Meters

Logarithmic scale, with defeat switch, and sensitivity switch (–20 dB)–50 dB to +3 dB (indication in dB and %)m Power Requirements

AC 120 V/230 V, 50/60 Hz(Voltage as indicated on rear panel)m Power Consumption

235 watts idle
430 watts in accordance with IEC 60065

m Maximum Dimensions

Width 465 mm (18-5/16")
Height 211 mm (8-5/16")
Depth 464 mm (18-1/4")

m Mass30.9 kg (68.1 lbs) net
38.0 kg (83.8 lbs) in shipping carton

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.

n Supplied accessorymm

AC power cord

Specifications and design subject to change without notice for improvements.

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