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

Pure Class A power amplifier with power MOS-FET 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 MOS-FET 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 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 level oftechnical know-how that is second to none.
Each model in the A-65/A-45/A-35 lineup hasreceived high praise, both for sound quality andperformance. The A-46 is a minor-change
successor to the A-45, positioned as themedium power level model of the series.
Naturally, the A-46 also demonstrates the sameunwavering dedication to sound quality andoutstanding design policy which are thehallmark of Accuphase. This pure class A stereo
power amplifier with its distinctive external heatsinks 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. Thepower amplifier section features further
improved MCS+ topology and the renowned
current feedback approach. This results inelectrical characteristics that surpass even thedemanding standards set by its predecessors.
Employing only highest grade materials andstrictly selected parts, the A-46 realizes very low
output impedance which ensures that constantdrive voltage is available for the speakers.
The output stage features power MOS-FETsrenowned for their excellent sound and superiorreliability. For each channel, six of these devices
are arranged in a parallel push-pull class Aarrangement. 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 meansthat constant power is always supplied, regardlessof the presence or absence of a musical signal.
This makes the amplifier completely immune toexternal influences and ensures stable operation at
all times. The large heat sinks mounted on theoutside reliably prevent internal heat buildup,
allowing the amplifier to sustain output levels of asmuch as 360 watts per channel into 1 ohm (withmusic signals). If even higher power is required,bridged mode turns the A-46 into a high-grade
monophonic power amplifier.

■ Power modules with 6-parallel push-pull arrangement of power
MOS-FETs deliver a guaranteed linear output of 360 watts perchannel into 1 ohm (music signals only), 180 watts into 2 ohms, 90
watts into 4 ohms, or 45 watts into 8 ohms.
■ Amply dimensioned power supply with high-efficiency toroidaltransformer and two large 47,000 µF filtering capacitors.
■ 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.

Power MOS-FETs■ Revised NFB design minimizes output impedance andincreases damping factor, resulting in further improved
sound quality.
■ Fully balanced input stage shuts out external noiseinterference.
■ Mode selector for easy switchingmono/stereo/bridged operation

between

Toroidal power transformerdual■ Front panel input type selector (line/balanced).
■ 4-step gain control (MAX, -3 dB, -6 dB, -12 dB) minimizes
residual noise.

Input selector■ Large analog power meters with operation/illuminationand sensitivity selector.

Gain selector■ Speaker protection uses semiconductor (MOS-FET)
switch. Elimination of mechanical switches assureslong-term reliability and improved signal purity,resulting in further improved sound quality.
■ PCB copper foil and all
major signal pathcomponents are goldplated.

MOS-FET switches■ Two sets of speaker
outputs, with large
terminals that accept also
Y lugs.

Meter circuitry assemblyParts selected for sound quality and reliability

Large speaker terminals

Q5

Q9

Q 13

Q7

Q 11

Q 15

Q 17

NFB
NETWORK+ B1

REGULATOR

Q1

Q3

Q 19

Q 21

Q 23

Q 25

Q 27

Q 29

Q 31+ B2

Bias stabilizer
circuitOUTPUT

Bias stabilizer
circuitOutput current (A)NFB
NETWORKGAIN CONTROLCIRCUIT
Bias stabilizer
circuitNFB
NETWORKQ2– INPUT

Line/balanced input connectors★ 1-ohm operation possible
with music signals onlyBias stabilizer
circuit+–Meter selector

Protection circuitry

Instrumentation amplifier+ INPUT

Filtering capacitors–+Q4

Q6Q 10

Q 14Q8Q 12

Q 16

Q 18

Q 20

REGULATOR

Q 22

Q 24

– B1

Bias stabilizer
circuit

Q 26

Q 28

Q 30

Q 32

– B2

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

MCS+ (Multiple Circuit Summing)

Figure 1 Circuit diagram of amplifier section (one channel)

Figure 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

Further refined MCS+ topology for evenlower noise

Current feedback principle assures excellent
phase characteristics in high range

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 inexcellent CMRR (common mode rejection

Accuphase's original MCS (Multiple CircuitSumming) configuration uses a number ofidentical circuits connected in parallel to achieve
superior performance characteristics. MCS+ isa further refined version of this approach. Byextending parallel operation to the class-A drivestage of the current/voltage converter, the noise
floor has been lowered further.

As shown in the illustration, the A-46 uses theoutput signal current rather than voltage forfeedback. 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 ofcircuit parameters.

Signal input stage＋ INPUTPower amplifier stage＋−NFB
NETWORK(+) input buffer＋NFB
NETWORK−OUTPUT

AmplifierOutput(-) input buffer
Current NFB
network−＋

Instrumentation amplifier configurationratio) and minimal distortion. Anothersignificant advantage is that external noiseand other external influences are virtually shutout. The result is a drastic improvement inoperation stability and reliability.

/V
converter

Trans-impedance amplifier

NFB
NETWORK− INPUT

Current adderPrinciple of current feedback amplifier■ Power amplifier assembly with six parallel push-pull
power MOS-FET pairs per channel mounted directly tolarge heat sink, MCS+ circuitry, and current feedback
amplifier.

Phase selector for balanced input● Inthe factory default
condition, the switch isset to the left side ("pine +"), as shown in theillustration.
● If the balanced output
oftheconnected
preamplifier has a "pinw +" arrangement, theswitch should be set tothe right side.

■ Using two A-46 units, bi-amping or bridged connection can be realized, for even higher performance. ■ In this case, only the LEFT input (BALANCED or LINE) of each unit is used.

Connection example for bi-amping setup
Left loudspeaker

Connection example for bridged setup

Right loudspeaker

Left loudspeaker＊ A speaker with a built-in crossover networkand separate inputs for LOW and HIGH range
is required.

− ○＋○− ○＋○LOW

HIGHRLR− ＋ − ＋＊ The − speaker terminals of the A-46 are not used.
− ○＋○− ○＋
○

LOW

−○＋
○−○L

RIGHT ＋A-46
for rightchannel
To left channel input

To left channel input

LLEFT ＋

A-46
for rightchannel
To left channel input

qTo left channel input

LMode selector of both A-46 units
set to DUAL MONO positionw

LEFT ＋RIGHT ＋

A-46
for leftchannelRPreamplifier＋○HIGH− ＋ − ＋

A-46
for leftchannel■ Front panel

Right loudspeakerIn bridged mode, the A-46 becomes amonophonic amplifier with even higher power
output.

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

“BRIDGE” LED on front
panel of both A-46 units lit

RMode selector of both A-46units set to BRIDGE position

Preamplifier

A-46 Guaranteed Specifications[Guaranteed specifications are measured according to EIA standard RS-490.]● Continuous Average Output Power (20 - 20,000 Hz)
Note: Load ratings marked (＊) apply only to operation with music signals.
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(bridged connection)er■ Rear paneltiyu!2720 watts into
360 watts into180 watts into

2 ohms (＊)
4 ohms
8 ohms● Total Harmonic Distortion
Stereo operation (both channels driven)
0.05% with 2 ohms load
0.03% with 4 to 16 ohms load
Monophonic operation (bridged connection)
0.05% with 4 to 16 ohms load
● Intermodulation Distortion 0.01%● Frequency Response

At rated output: 20 - 20,000 Hz +0, -0.2 dB
At 1 watt output: 0.5 - 160,000 Hz +0, -3.0 dB● Gain28.0 dB (with GAIN selector at MAX)(in stereo and bridged operation)● Gain Selection

MAX, -3 dB, -6 dB, -12 dB● Output Load impedance Stereo operation: 2 to 16 ohms
Bridged operation: 4 to 16 ohms
With music signals only, 1-ohm loads are permissible for stereo
operation and 2-ohm loads for bridged operation.

● Damping Factor

500● Input Impedance

Line: 20 kilohms● 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
Bridged operation:
1.51 V for rated output
0.11 V for 1 watt output
Balanced: 40 kilohms● Signal-to-Noise Ratio(A-weighted, input shorted) 115 dB (GAIN selector in MAX position)

o !0!1q Right/left-channel output power meters(dB and % scale)w Function indicators
METER -20 dB SPEAKER A, B
LINE BALANCED BRIDGEe Meter operation/illumination and sensitivity selector
OFF, 0 dB, -20 dB
r Speaker selector buttons
A: ON/OFF, B: ON/OFFt Power switch
y Input selector button
LINE, BALANCED!3★
u Gain selector
MAX, −3 dB, −6 dB, −12 dB
i Line inputs
o Balanced inputs
Pin (2) − Pin (3) +(Can be switched with phase selector switch !1)!0 Mode selector
DUAL MONO, NORMAL, BRIDGE!1 Balanced input phase selector switch!2 Right/left-channel speaker output terminals
A/B, 2 sets
!3 AC power supply connector★

120 dB (GAIN selector in −12 dB position)
At rated output● Speaker leakage levelat OFF setting-55 dB or less (10 kHz, 8 ohm load)● Output Level Meters-60 dB to +3 dB (indication in dB and %)Logarithmic scale, with illumination off switch andsensitivity selector (-20 dB)● Power Requirements

AC 120 V/220 V/230 V, 50/60 Hz(Voltage as indicated on rear panel)● Power Consumption

200 watts idle
410 watts in accordance with IEC 60065● Maximum Dimensions

Width 465 mm (18-5/16")
Height 211 mm (8-5/16")
Depth 464 mm (18-1/4")● Mass31.9 kg (70.3 lbs) net
39.0 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 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

Specifications and design subject to change without notice for improvements.
E1105YPRINTED IN JAPAN

851-0205-00（B1）