Accuphase A-65 Brochure

m Pure Class A operation delivers quality power: 60 watts × 2 into 8 ohms m Power MOS-FET

output stage features 10-parallel push-pull conﬁ guration and delivers linear high power progression to ultra-low 1-ohm impedances m Input section conﬁ gured as instrumentation ampliﬁ er m Further improved MCS+ circuit in ampliﬁ er section m Current feedback topology combines stable operation with outstanding sound m Bridged mode allows upgrading to monophonic ampliﬁ er m Two selectable meter types: digital power meters showing true power values and bar graph indicators

Pure Class A power ampliﬁ er with power MOS-FET devices — Input stage features ful-

ly balanced signal paths as found in high-quality instrumentation ampliﬁ ers. Further

reﬁ ned MCS+ topology and current feedback result in superb sound quality and out-

standing performance parameters. Strong power supply section and power MOS-FET

devices in ten-parallel push-pull conﬁ guration sustain linear power output progression

down to impedances as low as 1 ohm. Digital power meters show true power readings.

The combination of pure class A and power MOS-FET devices to realize high output power with excellent sonic purity is a domain where Accuphase excels. Models such as the A-100, A-50V, and A-60 have achieved legendary status among audiophiles and represent an unrivaled level of technological excellence. As a model-change successor to the A-60, the new A-65 incorporates accumulated Accuphase know-how while featuring a number of further improvements. The input stage is conﬁ gured as an instrumen- tation ampliﬁ er to allow fully balanced input signal paths. The further reﬁ ned MCS+ topology pushes noise and dis- tortion down to absolutely minimal levels, and strictly selected materials and parts of the highest quality are used throughout. The end result is a high-end class A stereo ampliﬁ er with simply stunning performance and sound quality.

The output stage of the A-65 features power MOS-FETs renowned for their excellent sound and superior reliability. For each channel, ten of these devices are arranged in a parallel push-pull arrangement. MOS-FETs have excellent frequency characteristics, and their high input impedance reduces the load imposed on the preceding drive stage. They also have negative thermal characteristics, which ensures perfect operation stability. Driving these devices in pure class A produces rich, high-deﬁ nition sound that brings out the ﬁ nest nuances in the music. In a pure class A ampliﬁ er, the power provided by the power supply is always constant, regardless of the presence of a musical signal. This means that the ampliﬁ er remains unaffected by ﬂ uc- tuations in voltage and other external inﬂ uences.

On the other hand, it also means that the output stage generates considerable thermal energy. In the A-65, this is dissipated effectively by large heat sinks which provide ample capacity to remove the heat produced by the internal circuitry. The high-efﬁ ciency toroidal power transformer housed in an aluminum diecast enclosure, in conjunction with amply dimensioned smoothing capacitors, provides the muscle to deliver an astonishing 480 watts per channel into a 1-ohm load (music signals only). If even higher power reserves are required, bridged mode turns the A-65 into a superlative monophonic power ampliﬁ er.

n Power modules with 10-parallel push-pull arrangement of power MOS-FETs

deliver 480 watts per channel into 1 ohm (music signals), 240 watts into 2 ohms, 120 watts into 4 ohms, or 60 watts into 8 ohms.

n Strong power supply with high-efﬁ ciency toroidal transformer and two

extra-large 82,000 μF ﬁ ltering capacitors.

Bridged mode supports upgrading to monophonic ampliﬁ er with 960 watts

into 2 ohms (music signals), 480 watts into 4 ohms, or 240 watts into 8 ohms.

n Instrumentation ampliﬁ er principle allows fully balanced signal paths, and

current feedback ampliﬁ er topology drastically improves S/N ratio.

n Four gain control settings (MAX, –3 dB, –6 dB, –12 dB) minimize residual

noise.

n Fully balanced input stage shuts out external noise interference. n Dual mode power meters, switchable to 5-digit numeric readout or 25-point

LED bar graph indication.

● Meter circuit ON/OFF switch.

● Digital power meters show true

output power values, based on output current detected by a Hall element.

● Peak value hold time settings: 1 second, .

n Input selector button (balanced/unbalanced) on front

panel.

n Mode selector with dual mono position supports bi-

amping.

n Oversize speaker terminals accept also Y lugs.

Meter circuitry/control circuitry assembly

Large speaker terminals

Toroidal power transformer

Filtering capacitors

Hall element

Mode selectorGain selector

Unbalanced and balanced input connectors

Instrumentation ampliﬁ er

+ B3

INPUT

NFB

NETWORK

GAIN

CONTROL

NFB

NETWORK

INPUT

Gain control

Figure 1 Circuit diagram of ampliﬁ er section (one channel)

Bias stabilizer

circuit

Q11Q

Q10Q

Q12Q

Bias stabilizer

circuit

Bias stabilizer

circuit

Bias stabilizer

circuit

MCS+ (MultipleCircuit Summing)

REGULATOR

Bias stabilizer

circuit

REGULATOR

NFB

NETWORK

+ B1

Q25Q27Q29Q

Q26Q28Q30Q

10-parallel push-pull

power MOS-FET array

547W

+ B2

OUTPUT

Power MOS-FETs

Output current (A)

0 5 10 15 20 25 30 35

Output voltage (V)

 1-ohm operation

Figure 2 Load impedance vs. outpu

(output voltage/output cur

365W

214W

118W

61W

with music signal

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