● Pure Class A operation delivers quality power: 45 watts x 2 into 8 ohms ● PowerMOS-FET output stage features 6-parallel push-pull configuration ● Instrumentation
amplifier principle used in amplification stage ● Further evolved MCS+ circuit
topology ● Current feedback principle combines stable operation with outstanding
sound quality ● Bridged connection mode allows upgrading to monophonicamplifier ● Large high-efficiency toroidal power transformer ● 4-stage gain control

The Exhilaration of Pure Class A
An amplifier operating in pure Class A always produces
its full rated output power, regardless of the actual output requirement. This no-holds-barredapproach which requires a hefty power supply and output stage results in fabulous audio
performance, making such a power amplifier the dream of audiophiles worldwide. The PureClass A Stereo Power Amplifier A-47 represents the state of the art in this field. Featuring
large external heat sinks that allow well balanced dimensions, it delivers 45 watts ofimpeccable power into 8 ohms, taking the listener into a new realm of musical enjoyment.
The history of Pure Class A power amplifiers fromAccuphase began in 1978 with the introduction of themodel P-400. The company has been perfecting thetechnology ever since, developing numerous technological improvements along the way. The A-47 is a successor model to the A-46, based on the design technology
developed for higher-ranked models. It is a full-fledged
Pure Class A Stereo Amplifier that produces truly
captivating sound.
The output stage of the A-47 uses high-performance
power MOS-FETs ideal for audio applications. For eachchannel, six devices are arranged in a parallel push-pull
Pure Class A arrangement. This results in very low
output impedance, ensuring that constant drive voltage
is available also for low-impedance loads. Superior
performance is evident from the linear power progres-sion of 45 watts into 8 ohms, 90 watts into 4 ohms, and180 watts into 2 ohms. The amplifier is even capable ofdriving ultra-low 1-ohm impedances with an amazing
360 watts (music signals only).
The input stage circuitry is configured as an instrumentation amplifier. This approach makes it possible toachieve fully balanced signal paths, extending from thesignal input all the way to the final power amp stage.
Extremely low-distortion, low-noise op amps are used in
the input stage, combined with measures to prevent any
risk of noise intrusion from the input circuitry. As a result,
S/N ratio has been further improved.
The A-47 not only eliminates any possible internalsource of noise or distortion, as demonstrated by its
outstanding performance ratings, it is also highly
impervious to changes in ambient conditions. As aconsequence, operation stability and reliability which arecrucial for a power amplifier have been dramaticallyenhanced.
Only the finest parts and materials, selected as aresult of a series of strict testing are used in the A-47.
Latest circuit topology raises electrical performanceby another notch, ensuring excellent long-term
reliability and producing a further improvement insound quality. The front panel of the amplifier
prominently features two large analog power meters,with switchable peak hold and sensitivity. An on/off
switch for the meters is also provided. Using the A-47
in bridged mode creates a mono amplifier with evenmore impressive power output capability, rated for
180 watts into 8 ohms, 360 watts into 4 ohms, and720 watts into 2 ohms (music signals only).

Features and Functions■ Power modules with 6-parallel push-pull arrangement of power MOS-FETsdeliver a guaranteed linear output of 45 watts per channel into 8 ohms, 90 watts
into 4 ohms, 180 watts into 2 ohms, or 360 watts into 1 ohm (music signals only).
■ Strong power supply with massive high-efficiency toroidal transformer andtwo large 56,000 µF filtering capacitors.
■ Bridging allows upgrade to monophonic amplifier with even higher power,delivering 180 watts into 8 ohms, 360 watts into 4 ohms, or 720 watts into
2 ohms (music signals only).
■ Fully balanced input stage shuts out external noise interference.
■ Shortest output signal path length minimizes output impedance and realizes
damping factor of 600 or more.
■ Input selector button on front panel allows switching between line andbalanced signals.
■ 4-stage gain selector (–12 dB, –6 dB, –3 dB, MAX) also minimizes residual noise.
■ Large analog power meters with operation/illumination/peak hold switch andsensitivity selector.

Large toroidal power transformer

Filtering capacitors

Line and balanced input connectors

Phase selector

Gain selector

MOS-FET switches■ Operation mode selector supports dual mono or stereo operation and allows
bi-amping connection.
■ Phase selector for balanced inputs.
■ Semiconductor (MOS-FET) switches used for protection circuitry prevent
contact problems and ensure long-term reliability. Eliminating mechanicalcontacts from the signal path also further enhances sound quality.
■ PCB copper foil and all major
Powerful output
Shortest connection
signal path components arestage
between amplifier and terminals
gold-plated.
＋ side sensing■ Two sets of large speakerterminals (A / B) also accept Y＋lugs.
PowerProtectionSpeaker
Power amplifier
amplifierProtection circuit
circuitterminals
assembly
assembly
assemblyassembly■ Balanced remote sensing tech－
nology provides balanced feed－ side sensingback from near the speakerterminals to ensure low impedBalanced remote sensing
ance and high damping factor.

Meter controls

Massive speaker terminals with extra thickmetal bars connected directly to output PCB

Operation mode selector

Protection circuit assembly

Assembly with meter circuitry

Parts selected for high sound quality
and reliability

Low-noise instrumentation amplifier configuration and further refined MCS+ topology
Low-noise instrumentation amplifier allows
balanced signal paths

MCS+ (Multiple Circuit Summing) circuit inamplifier section drastically improves S/N ratio

Current feedback principle assures excellent
phase characteristics in high range

The balanced input stage circuitry features instrumentation amplifier topology such as used in high-precision measuring equipment. This approach ensures
perfectly matched input conditions for the positive andnegative side and thereby allows the realization ofhigh-performance balanced signal transmission.

The input stage of the amplifier section features
another Accuphase innovation: MCS+ (MultipleCircuit Summing). This innovative method further
reduces noise and at the same time ensuresrock-stable performance.

As shown in the illustration, the A-47 uses the output
signal current rather than the 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. This principle is ideally suited to the circuitryof a power amplifier that has to handle a wide range ofsignals, from extremely low levels to dynamic, high-volume situations, while maintaining excellent stability.

Signal input stage+ INPUTPower amplifier stage+–
NFB
NETWORKGAIN CONTROLCIRCUIT+

Trans-impedance
amplifier
OUTPUT－INPUT–

Buffer–+

Instrumentation amplifier configuration

AmplifierCurrent adder

NFB
NETWORK– INPUT

I -V
converter＋INPUT

BufferCurrent NFB
network

Principle of current feedback amplifier

OUTPUTCircuit diagram of amplifier section (one channel)
Signal input stage

MCS+ (Multiple Circuit Summing)

Output power characteristics
438W

440

Power MOS-FETs

400

Q1
Q5

INPUT＋－Q7
Q3

NFB
NETWORKREGULATOR

Q9

Q 11

Q 13

Q 15

B2
Q 17

Q 19

Q21

Q23

Q25

Q27

Q29

Q31

6-parallel push-pull
configuration

Biasstabilizer
circuitNFB
NETWORK－Q2＋OUTPUTBiasstabilizer
circuitBiasstabilizer
circuitNFB
NETWORK320281W

280
240

194W

200120180W

102W

8090W

40Q6Q 10Q 14Q8Q 12Q 16

Q4360W

160

GAIN CONTROLCIRCUIT

INPUT

360

B1Output power (W)Biasstabilizer
circuit

Q 18

Q 20

Q22

Q24

Q26

Q28

Q30

Q32
32

B2Max. output power
Rated output power

45W
8Ω4Ω

2Ω

1Ω

Impedance (Ohms)
Biasstabilizer
circuit

REGULATOR

B1

High-performance power MOS-FETs for audio applications

Power amplifier assemblyPower amplifier assembly with 6-parallel push-pull power
MOS-FET arrangement for output stage mounted directly
to large diecast aluminum heat sink, also comprising
MCS+ circuitry and current feedback amplifier. Twocompletely identical circuits are used for left and right.

■ Using two A-47 units, upgrade to bridged operation or bi-amping is possible. ■ Use the LEFT (BALANCED or LINE) input connectors for both units.

Connection example for bridged setup
Left loudspeaker－●Connection example for bi-amping setup
Right loudspeaker

Setting the operation mode selector tobridged mode turns the A-47 into amonophonic amplifier with four times higheroutput than in stereo mode. This creates asource of abundant high-quality power.

＋●－ speaker terminals of the A-47 are not＊ The ●used.

RIGHT ＋

A-47 for left channel

LEFT ＋

RIGHT ＋To left channel input

L"BRIDGE" LEDon front panel ofboth A-47 units
lit.

－●

＋
●－ ●
＋
●
－ ●
＋
●
LOW HIGH

LEFT ＋

A-47 for left channel

Mode selector ofboth A-47 units
set to BRIDGE.

Preamplifier

selector
OFF / NORMAL /HOLD (∞)❹ –20 dB button

To left channel input

RMode selector ofboth A-47 units setto DUAL MONO.

Rear Panel❻ Power switch

A: ON/OFF B: ON/OFFA-47 for right channel

To left channel inputPreamplifier❾ Line inputs–20 dB METER / SPEAKER A,B / LINE /BALANCED / BRIDGE❺ Speaker selector buttons－ ●＋●－ ●＋
●HIGH

LOW

－ ＋ － ＋LR

❶ Right/left-channel output power meters ❷ Function indicators❸ Meter operation＊ The speakers must have a built-in crossover network and separate inputs for LOW
and HIGH range.

－ ＋ － ＋Front Panel(dB and % scale)

Right loudspeaker

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

A-47 for right channel

To left channel input

Left loudspeaker

Balanced inputs[Pin ② ( – ) Pin ③ (＋) ](Can be changed with phase selectorswitch )Right/left-channel speaker
output terminals
A / B, 2 sets

❽ Gain selector–12 dB / –6 dB /–3 dB / MAX❼ Input selector button
LINE / BALANCED

Operation mode selector
DUAL MONO /NORMAL / BRIDGE

Balanced input phaseselector switch

AC power supplyconnector★

A-47 Guaranteed Specifications [Guaranteed specifications are measured according to EIA standard RS-490.]● Continuous Average Output Power (20 - 20,000 Hz)

Note: Ratings marked with (＊) are for music signals only.

Stereo operation
360 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 720 watts
into 2 ohms (＊)(bridged connection) 360 watts
into 4 ohms
180 watts
into 8 ohms
Stereo operation (both channels driven)● Total Harmonic
Distortion
0.05%
with a 2-ohm load
0.03%
with a 4 to 16-ohm load
Monophonic operation (bridged connection)
0.05%
with a 4 to 16-ohm load
● Intermodulation Distortion 0.01%● Frequency Response At rated continuous average output:
20 - 20,000 Hz +0, – 0.2 dB
At 1 watt output: 0.5 - 160,000 Hz +0, –3.0 dB
28.0 dB (GAIN selector in MAX position)● Gain(Stereo/monophonic operation)–12 dB, –6 dB, –3 dB, MAX● Gain Selection● Output Load impedance
Stereo operation:
2 to 16 ohms
Monophonic operation: 4 to 16 ohms
＊With music signals only, 1-ohm loads arepermissible for stereo operation and 2-ohm loads
for bridged operation.

600● Damping Factor● Input Sensitivity (with 8-ohm load, GAIN selector in MAX position)
Stereo operation:
0.76 V for rated continuous average output
0.11 V for 1 watt output
Monophonic operation: 1.51 V for rated continuous average output
0.11 V for 1 watt output● Input Impedance
Balanced: 40 kilohms
Line:20 kilohms● S/N ratio (A-weighted, with input shorted)
116 dB (GAIN selector in MAX position)
121 dB (GAIN selector in –12 dB position)
At rated continuous average output– 40 dB to +3 dB (indication in dB and %)● Output Level Meters
Logarithmic scale, with illumination off switch and sensitivity
selector (–20 dB)● Power Requirements 120 V, 220 V, 230 V AC (voltage as indicated on rear panel),
50/60 Hz200 watts idle
● Power Consumption
410 watts in accordance with IEC 60065
465 mm (18-5/16")● Maximum Dimensions WidthHeight
211 mm (8-5/16")
Depth
464 mm (18-1/4")
32.1 kg (70.8 lbs) net● Mass39.0 kg (86.0 lbs) in shipping carton

Remarks★ This product is available in versions for 120/220/230 V AC. Make sure that the voltage shown on the rear panel matches the AC line voltage in your area.
★ The 230 V version has an Eco Mode that switches power off after 120 minutes of inactivity.
★ 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

●The specifications and appearance of this product are subject to change without notice.
G1505Y PRINTED IN JAPAN 850-2193-00（B1）