Accuphase A-46 User Manual

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Page 1

●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 ● sound ●

●



Current feedback combines stable operation with outstanding



Bridged mode allows upgrading to true monophonic amplifier



Large high-efficiency toroidal transformer ●4-step gain control

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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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Instrumentation amplifier and further refined MCS+ topology

Instrumentation amp configuration allows fully balanced signal paths

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 in excellent CMRR (common mode rejection

Signal input stage

NFB

NETWORK

＋

−

NFB

NETWORK

NFB

NETWORK

−

＋

INPUT

−



INPUT

Instrumentation amplifier configuration

Power amplifier stage

＋

−

OUTPUT

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 even lower noise

Accuphase's original MCS (Multiple Circuit Summing) configuration uses a number of identical circuits 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 of the current/voltage converter, the noise floor has been lowered further.

■

Power amplifier assembly with six parallel push-pull power MOS-FET pairs per channel mounted directly to large heat sink, MCS+ circuitry, and current feedback amplifier.

Current feedback principle assures excellent phase characteristics in high range

As shown in the illustration, the A-46 uses the output signal current rather than 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.

(+) input buffer

(-) input buffer

Current adder

converter

Trans-impedance amplifier

Current NFB

network

Amplifier

Principle of current feedback amplifier

Output

Phase selector for balanced input

●

In the factory default condition, the switch is set to the left side ("pin e +"), as shown in the illustration.

●

If the balanced output of the connected preamplifier has a "pin

+" arrangement, the

switch should be set to the right side.

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■

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 Connection example for bridged setup

＋−＋

−

Right loudspeaker

＋○−

○＋○−○

LOW

HIGH

−○＋

○

Left loudspeaker Right loudspeakerLeft loudspeaker

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

＊A speaker with a built-in crossover network

HIGH

and separate inputs for LOW and HIGH range is required.

LRL

＋−＋

−

LOW

＋○−○＋○−

○

In bridged mode, the A-46 becomes a

monophonic amplifier with even higher power

output.

−

＊ The speaker terminals of the A-46 are not used.

RIGHT

＋ RIGHT

LEFT＋

−○＋

○

＋

LEFT＋

A-46

for left

channel

To left channel input To left channel input

Preamplifier Preamplifier

■ Front panel

er tyu

■ Rear panel

!0 !3

o!1

q Right/left-channel output power meters

(dB and % scale)

w Function indicators

METER −20 dB SPEAKER A, B LINE BALANCED BRIDGE

Meter operation/illumination and sensitivity selector

OFF, 0 dB, −20 dB

r Speaker selector buttons

A: ON/OFF, B: ON/OFF

t Power switch y Input selector button

LINE, BALANCED

Mode selector of both A-46 units set to DUAL MONO position

q w

!2i

★

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

!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

★

A-46 for right channel

A-46

for left

channel

To left channel input To left channel input

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

A-46 Guaranteed Specifications

[Guaranteed specifications are measured according to EIA standard RS-490.]

● Continuous Average Output Power (20 - 20,000 Hz)

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

Total Harmonic Distortion

● Stereo operation (both channels driven)

0.05% with 2 ohms load

Monophonic operation (bridged connection)

●

Intermodulation Distortion

● 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

● Gain 28.0 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

● Damping Factor 500

● 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

● Input Impedance Line: 20 kilohms Balanced: 40 kilohms

● Signal-to-Noise Ratio

(A-weighted, input shorted)

120 dB (GAIN selector in −12 dB position) At rated output

● Speaker leakage level at OFF setting −55 dB or less (10 kHz, 8 ohm load)

● Output Level Meters −60 dB to +3 dB (indication in dB and %)

● 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")

● Mass 31.9 kg (70.3 lbs)net

39.0 kg (86.0 lbs) in shipping carton

Note: Load ratings marked (＊) apply only to operation with music signals.

0.03% with 4 to 16 ohms load

0.05% with 4 to 16 ohms load

0.01%

With music signals only, 1-ohm loads are permissible for stereo operation and 2-ohm loads for bridged operation.

115 dB (GAIN selector in MAX position)

Logarithmic scale, with illumination off switch and sensitivity selector (−20 dB)

A-46 for right channel

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

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

●

C power cord

●

Specifications and design subject to change without notice for improvements.

E1105Y PRINTED IN JAPAN 851-0205-00（B1）