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 configuration and delivers linear high power progression to ultra-low 1-ohm impedances m Input section configured as instrumentation amplifier m Further improved MCS+ circuit in amplifier section m Current feedback topology combines stable operation with outstanding sound m Bridged mode allows upgrading to monophonic amplifier m Two selectable meter types: digital power meters showing true power values and bar graph indicators

Pure Class A power amplifier with power MOS-FET devices — Input stage features fully balanced signal paths as found in high-quality instrumentation amplifiers. Further refined MCS+ topology and current feedback result in superb sound quality and outstanding performance parameters. Strong power supply section and power MOS-FET devices in ten-parallel push-pull configuration 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 configured as an instrumentation amplifier to allow fully balanced input signal paths. The further refined MCS+ topology pushes noise and distortion 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 amplifier 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-definition sound that brings out the finest nuances in the music. In a pure class A amplifier, the power provided by the power supply is always constant, regardless of the presence of a musical signal. This means that the amplifier remains unaffected by fluctuations in voltage and other external influences.

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-efficiency 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 amplifier.

nPower 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-efficiency toroidal transformer and two extra-large 82,000 μF filtering capacitors.

n Bridged mode supports upgrading to monophonic amplifier with 960 watts into 2 ohms (music signals), 480 watts into 4 ohms, or 240 watts into 8 ohms.

nInstrumentation amplifier principle allows fully balanced signal paths, and current feedback amplifier 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.

nDual 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, .

Toroidal power transformer

Filtering capacitors

Hall element

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.	Gain selector	Mode selector

Meter circuitry/control circuitry assembly

Large speaker terminals Unbalanced and balanced input connectors

Instrumentation amplifier

REGULATOR

+ B1

Bias stabilizer

25

circuit

+ B3

10-parallel push-pull

547W

Q1

Q19

power MOS-FET array

+ B2

Q5

Q9

Q13

20

+

Q17

Q21

Q23

Q25

Q27

Q29

Q31

Q33

Q35

Q37

Q39

Q41

+INPUT

Q7

Q11

Q15

-

Q3

NFB

Bias stabilizer

15

NETWORK

circuit

365W

NFB

GAIN

NETWORK

OUTPUT

CONTROL

(A)

Bias stabilizer

Bias stabilizer

10

NFB

current

circuit

circuit

NETWORK

Q6

Q10

Q14

Output

214W

Q2

-

Q18

Q20

Q24

Q26

Q28

Q30

Q32

Q34

Q36

Q38

Q40

Q42

5

+

-INPUT

118W

- B2

Q8

Q12

Q16

61W

Q4

Q22

- B3

0

0

5

10

15

20

25

30

35

Bias stabilizer

circuit

Output voltage (V)

- B1

REGULATOR

1-ohm operation p

Gain control

MCS+ (MultipleCircuit Summing)

with music signal

Figure 2 Load impedance vs. output

Figure 1 Circuit diagram of amplifier section (one channel)

Power MOS-FETs

(output voltage/output curr