● Pure Class A operation delivers quality power: 60 watts x 2 into 8 ohms ● Power MOS-FET output
stage features 10-parallel push-pull configuration and delivers linear high power progression to ultra-low
1-ohm impedances ● Ultra low-noise instrumentation amplifier principle used in input stage ● Amplification
stage implements further evolved MCS+ topology ● Current feedback principle combines stable operation
with outstanding sound quality ● Bridged connection mode allows upgrading to monophonic amplifier● Two selectable meter types: digital power meters showing true power values and bar graph indicators

Ushering in a New Era
The Ultimate Pure Class A Stereo Power Amplifier. Input stage
features fully balanced signal paths realized with ultra low noise instrumentation amplifier
topology in discrete configuration. MCS+ design and current feedback in amplification
circuitry deliver S/N ratio and sound quality on a level unrivaled by any stereo power
amplifier. Massive power supply and power MOS-FET devices in ten-parallel push-pull
configuration sustain linear power output progression down to impedances as low as 1 ohm.
Output stage with further lowered impedance realizes a damping factor of 800.
In 2012, on the occasion of the company's 40thanniversary, Accuphase released the Pure Class A
Monophonic Power Amplifier A-200, an epoch-making
product that elevated performance and sound quality
to a whole new level, garnering the highest praisefrom experts around the world. Inheriting many
outstanding technology features of the A-200, theA-70 represents a full model change from the A-65,
ready to take its place as the ultimate pure class A
stereo power amplifier.
The alluring sound of properly executed pure class A
operation has always been an object of aspiration for
the true audiophile. Accuphase has a long anddistinguished history in this field, accumulating a
wealth of know-how and expertise over the years.
While reflecting this tradition, the A-70 also
implements latest technology such as the ultra
low-noise instrumentation amplifier principle realized ina discrete configuration, along with optimized signal
input and power amplification stages, resulting in anastonishing 127 dB S/N ratio (at -12 dB gain),surpassing even the formidable earlier Accuphasestereo amplifier lineup. Strictly selected parts andmaterials of the highest grade further contribute topeerless performance and supreme sound quality.
The output stage of the A-70 features power
MOS-FETs renowned for their excellent frequency
response, sonic performance, and superior reliability.
For each channel, ten of these devices are arranged
in a parallel push-pull configuration driven in pureclass A. The power supply features a large toroidal
power transformer equipped with thermal dissipation
fins, along with two oversized 82,000 µF filtering
capacitors, which provides plenty of reserves toensure linear power progression down to ultra low
1-ohm impedances. In the output circuitry,
ultra-heavy-gauge edgewise coils with a surface area
more than three times larger than conventional units,
combined with MOS-FET switches are used in placeof relays, to eliminate mechanical contacts andimprove long-term reliability. Top-grade materials,
sophisticated circuit pattern technology, and various
other measures result in low impedance and enable
the realization of a damping factor of 800, which
represents a two-fold improvement over the A-65. The
power meters are designed to provide meaningful
information and offer a choice between true power
readings in digital format and bar graph indication
representing voltage values.

■ 10-parallel push-pull arrangement of power
MOS-FETs delivers linear power progression: 480watts (music signal) into 1 ohm, 240 watts into 2ohms, 120 watts into 4 ohms, or 60 watts into 8ohms.
■ Strong power supply uses massive high-efficiency
toroidal transformer with reinforced shielding forminimal leakage flux, along with two large
82,000 µF filtering capacitors.
Filtering capacitors
Large toroidal transformer■ Power meters with output level indication
switchable between 5-digit numeric readout
and 32-point LED bar graph.
● Meter operation on/off switch.
● Digital power meter showing true power values,
Digital power meter/bar graph meterbased on output current detected by a Hallelement● Switchable peak hold time: 1 second or infinite■ 4-stage gain selector (MAX, -3 dB, -6 dB, -12 dB) also
minimizes residual noise.
■ Operation mode switch supports dual mono operation
and allows bi-amping connection.
Gain control selector
Hall elements■ Bridging allows upgrade to monophonic amplifier witheven higher power, delivering 960 watts into 2 ohms
(music signal), 480 watts into 4 ohms, or 240 watts into8 ohms.
■ Instrumentation amplifier principle allows fully balanced
signal transmission. Current feedback amplification
circuit drastically improves signal/noise ratio.
■ Two sets of large speaker terminals enable easy
Operation mode selector
Ultra-heavy-gauge edgewise coilbi-wiring connection.
■ Semiconductor (MOS-FET)
switches used for protection
circuitry prevent contact problems and ensure long-term
reliability. Eliminating mechanical contacts from signal
path also further enhancessound quality.
Parts selected for high sound quality and reliability

MOS-FET switches

Major signal path parts are gold-plated

Microprocessor assembly

Protection circuit assembly

Output power characteristics
Signal input stage GAIN 22 dB

Signal amplification stage GAIN 6 dB
MCS+ (Multiple Circuit Summing)

GAIN < MAX, -3, -6, -12 dB >

547W

550

Power MOS-FETs

500
450

Biasstabilizer
circuit480W+ B1
Q5＋+ B3

Q19Q17−FEEDBACK
NETWORK+ B2Q9PREAMPLIFIER

Q2Q6

Q23

Q10Output power (W)Q1+ INPUT

400

Q13Q25Q27Q29Q31Q33

Q35

Q37

Q39

Q41

Q20
Q14Biasstabilizer
circuitGND

Biasstabilizer
circuit

INPUT

Bias
stabilizer
circuit

Q15

Q3250

Q7

Q11

Q8

Q12150232W
240W

GND
Q21131W

100120W

50Q18

Q22
Q24

PREAMPLIFIER

Q26

Q28

Q30

Q32

Q34

Q36＋

Q4300

OUTPUTNFBNETWORK−350200

GAIN CONTROLCIRCUITFEEDBACKNETWORK370W

Q38Q40Q42

B3Max. output power
Rated output power

B2Q16B1Biasstabilizer
circuitNFB
NETWORK−＋Circuit diagram of amplifier section (one channel)

Power MOS-FETs

60W
8Ω

4Ω
2Ω
1Ω
Impedance (Ohms)

Ultra low-noise instrumentation amplifier configuration and further refined MCS+ topology
Amplification stage features ultra low-noise
instrumentation amplifier topology forfully balanced signal paths
The newly adopted ultra low-noise instrumentation amplifier principle is realized with discrete components, allowing optimization of
the redesigned signal input stage and power
amplification stage, and resulting in a 6 dB
improvement in signal-to-noise over the A-65.
Approaching the A-200's pinnacle performance, the A-70 is rated for 127 dB (at -12dB gain) or 121 dB (at maximum gain). TheSignal input stage+ INPUTPower amplifier stage

performance characteristics. MCS+ is a further
refined version of this approach. By extending
parallel operation to the class-A drive stage ofthe current/voltage converter, the noise floor has
been lowered further.

+–FEEDBACK
NETWORKGAIN CONTROLCIRCUIT+–FEEDBACK
NETWORK–– INPUT

entire power amplifier including theinput stage is configured as a symmetrical push-pull
circuit with fullybalanced signal
paths. Outstanding performance
Input connectors andcharacteristics inbalanced amplifier assemblyclude excellent
resistance against external noise and minimal
THD. The amplifier also is impervious againstchanges in ambient conditions, resulting infurther improved operation stability.

+Instrumentation amplifier principle

OUTPUT

Further refined MCS+ topology for evenlower noise
Accuphase’s original MCS (Multiple CircuitSumming) principle uses a number of identicalcircuits connected in parallel to achieve superior

Current feedback principle assures excellent
phase characteristics in high range
As shown in the illustration, the A-70 uses theoutput signal current rather than voltage
for feedback. Since the impedance at thecurrent feedback point is very low, there isalmost no phase shift. A minimal amountof NFB therefore results in maximum
improvement of circuit parameters.

Power amplifier assemblyPower amplifier assembly with 10-parallelpush-pull power MOS-FET arrangementfor output stage mounted directly tomassive 7.4 kg diecast aluminum heatsink, also comprising MCS+ circuitry andcurrent feedback amplifier. Twocompletely identical circuits are used.

Trans-impedance amplifier- INPUT

BufferI /Vconverter

Amplifier

OUTPUT
Current adder
Buffer+ INPUT

Current NFB
network

Principle of current feedback amplifier

Using two A-70 units, upgrade to bridged operation or bi-amping is possible.

Use the LEFT (BALANCED or LINE) input connectors for both units.

Connection example for bridged setup
Left loudspeaker

Connection example for bi-amping setup
Right loudspeakerIn bridged mode, the A-70 becomes amonophonic amplifier with even higher
power output.

Left loudspeaker− speaker terminals of the A-70 are not used.
＊The ●−＋＋−−＋ −LOWRIGHT ＋RIGHT ＋LEFT ＋＋−＋w−

To left channel input−＋To left channel input

Le＋＋HIGH

A-70
forrightchannel

Operation mode
selector set toBRIDGE on bothA-70 units

q＋ −

A-70
for
leftchannel

RBRIDGE LED on front
panel lit on both A-70
units

−

LOWTo left channel input

L■ Front Panel

HIGH−

A-70
for
rightchannel

To left channel input＊The speakers must have a built-in crossover networkand separate inputs for LOW and HIGH range.

＋LEFT ＋

A-70
forleftchannelRight loudspeaker

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

R

Preamplifierr

Operation mode
selector set toDUAL MONO on
both A-70 units

A-70 GUARANTEED SPECIFICATIONS[Guaranteed specifications measured according to EIA standard RS-490]● Continuous Average Output Power (20–20,000 Hz) Note: Load ratings marked (＊) apply only tooperation with music signals.

Stereo operation(both channels driven)

Monophonic operation(bridged connection)● Total HarmonicDistortionty■ Rear Panelu

i o !0Push this button to
open the sub panel!1!2!3!4q Hold time indicatorw Right/left-channel output power meters(digital and bar graph, switchable)e Bridge mode indicatorr Input type indicators
t Meter selector
OFF / ALL / dB / W
y Digital power meter range buttons
10W / 100W / 1000W
u Power switch
i Hold time selector button 1SEC /o Input selector button LINE / BALANCED● Intermodulation Distortion● Frequency Response● Gain● Gain Selection!5!6 ★

❿ Gain selector
MAX / -3 dB / -6 dB / -12 dB⓫ Right/left-channel speaker output terminals(same output at both sets)⓬ Line inputs!3 Balanced inputs② Inverted (–) ③ Non-inverted ( +)(Can be changed with phase selector
switch !4 )!4 Balanced input phase selector switch!5 Operation mode selector
DUAL MONO / NORMAL BRIDGE!6 AC power supply connector ★

480 watts per channel
into 1 ohm (＊)
240 watts per channel
into 2 ohms
120 watts per channel
into 4 ohms
60 watts per channel
into 8 ohms
960 watts
into 2 ohms (＊)
480 watts
into 4 ohms
240 watts
into 8 ohms
Stereo operation (both channels driven)
0.07%
with 2 ohm load
0.03%
with 4 to 16 ohm load
Monophonic operation (bridged connection)
0.05%
with 4 to 16 ohm load
0.01%
At rated output: 20 - 20,000 Hz +0, -0.2 dB
At 1 watt output: 0.5 - 160,000 Hz +0, -3.0 dB
28.0 dB (with GAIN selector at MAX)
(Stereo and monophonic operation)
MAX, -3 dB, -6 dB, -12 dB● Output Load impedance
Stereo operation:
2 to 16 ohms
Monophonic operation: 4 to 16 ohms
With music signals only, 1-ohm loads arepermissible for stereo operation and 2-ohm loads
for monophonic operation.
● Damping Factor
800● Input Sensitivity (with 8-ohm load, GAIN selector in MAX position)
Stereo operation:
0.87 V for rated continuous average output (60 W)
0.11 V for 1 watt output
Monophonic operation: 1.74 V for rated continuous average output (240 W)
0.11 V for 1 watt output● Input Impedance
Balanced: 40 kilohms Unbalanced: 20 kilohms● Signal-to-Noise Ratio (A-weighted, input shorted)
121 dB (GAIN selector at MAX)
127 dB (GAIN selector at -12 dB)
At rated continuous average output● Output Level Meters (digital indication and bar graph)
Digital meters: 5-digit indication, selectable range (10 W / 100 W / 1000 W)
Bar graph meters: 32-point scale
Hold time:
1 second/∞, switchable＊Display off setting provided＊Monophonic operation: same value for left/right● Power Requirements AC 120 V/230 V, 50/60 Hz(Voltage as indicated on rear panel)
280 watts idle
● Power Consumption
530 watts in accordance with IEC 60065
465 mm (18-5/16")● Maximum Dimensions WidthHeight
238 mm (9-3/8")
Depth
515 mm (20-1/4")
44.3 kg (97.7 lbs) net● Mass
54.0 kg (119.0 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.
230 V version has an Eco Mode that switches power off after 120 minutes of inactivity.
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

The specifications and appearance of this product are subject to change without notice.
D1405Y PRINTED IN JAPAN 850-2186-00（B1）