Accuphase A-46 User Manual

●Pure Class A operation delivers quality power: 45 watts x 2 into 8 ohms

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Power MOS-FET output stage features 6-parallel push-pull configuration

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Instrumentation amplifier principle ●Further improved MCS+ circuit topology ● sound ●

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Current feedback combines stable operation with outstanding

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Bridged mode allows upgrading to true monophonic amplifier

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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 Accuphase have long been blending the purity of class A operation with the superior performance of power MOS-FETs. Acclaimed by audiophiles the world over, these products reflect a level of technical know-how that is second to none. Each model in the A-65/A-45/A-35 lineup has received high praise, both for sound quality and performance. The A-46 is a minor-change successor to the A-45, positioned as the medium power level model of the series. Naturally, the A-46 also demonstrates the same unwavering dedication to sound quality and outstanding design policy which are the hallmark of Accuphase. This pure class A stereo power amplifier with its distinctive external heat sinks 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. The power amplifier section features further improved MCS+ topology and the 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, the A-46 realizes very low output impedance which ensures that constant drive voltage is available for the speakers. The output stage features power MOS-FETs renowned for their excellent sound and superior reliability. For each channel, six of these devices are arranged in a parallel push-pull class A arrangement. 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 means that constant power is always supplied, regardless of the presence or absence of a musical signal. This makes the amplifier completely immune to external influences and ensures stable operation at all times. The large heat sinks mounted on the outside reliably prevent internal heat buildup, allowing the amplifier to sustain 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-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 per channel 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 toroidal

transformer 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.

■ Revised NFB design minimizes output impedance and

increases damping factor, resulting in further improved sound quality.

■ Fully balanced input stage shuts out external noise

interference.

■ Mode selector for easy switching between dual

Toroidal power transformer

mono/stereo/bridged operation

■ Front panel input type selector (line/balanced).

■ 4-step gain control (MAX, -3 dB, -6 dB, -12 dB) minimizes

residual noise.

Large analog power meters with operation/illumination

■

and sensitivity selector.

■ Speaker protection uses semiconductor (MOS-FET)

switch. Elimination of mechanical switches assures long-term reliability and improved signal purity, resulting in further improved sound quality.

■ PCB copper foil and all

major signal path components are goldplated.

■ Two sets of speaker

outputs, with large terminals that accept also Y lugs.

Large speaker terminals

Meter circuitry assembly

Parts selected for sound quality and reliability

Power MOS-FETs

Filtering capacitors

Input selector

Gain selector

Meter selectorMOS-FET switches

Protection circuitry

Line/balanced input connectors

Instrumentation amplifier

INPUT

+ –

NFB

NETWORK

GAIN CONTROL

CIRCUIT

NFB

NETWORK

– +

– INPUT

Gain control

Bias stabilizer

circuit

Bias stabilizer

circuit

REGULATOR

NETWORK

REGULATOR

Q11Q

Q10Q

Q12Q

Bias stabilizer

circuit

Bias stabilizer

circuit

Bias stabilizer

circuit

MCS+ (Multiple Circuit Summing)

Figure 1 Circuit diagram of amplifier section (one channel)

★1-ohm operation possible

with music signals only

+ B1

NFB

Q23Q25Q27Q

Q24Q26Q28Q

–

B 1

Power MOS-FETs

6-parallel push-pull

+ B2

OUTPUT

–

B 2

Output current (A)

Output voltage (V)

Figure 2 Load impedance vs.

output power

(output voltage/output current)

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