CLASS-A STEREO POWER AMPLIFIER● Pure Class-A stereo power amplifier ● Power amplification stage withpower MOS-FETs in 6-parallel push-pull configuration ● Linear output
characteristics over entire load impedance range ● Instrumentation
amplifier topology ● Current feedback principle in amplification circuitry● Balanced Remote Sensing ● High damping factor of 800 ● Speaker
output protection circuit guards against short-circuiting ● Highly responsive
large peak power meters ● Suppor t for bi-amping and bridged mode

True Class-A stereo power amplifier with authentic musicality

Featuring a six-fold parallel push-pull architecture with power MOS-FETs, as well as ideal
gain allocation realized with discrete semiconductors in an instrumentation amplifier
configuration, the A-48 harnesses a wealth of advanced technology. Its outstanding
performance is exemplified by a signal/noise ratio of 117 dB, output of 360 watts into 1 ohm(music signals), and a damping factor of 800. The newly designed output protection circuit candetect any short-circuiting of the speaker terminals, for complete peace of mind. This power
amplifier is the ultimate instrument for immersive music appreciation on the highest level.

Technology development ahead of the curve
Instrumentation amplifier principle realizes excellent S / N ratio and linear output characteristics■ Instrumentation amplifier topology for improved

noise performance

The A-48 employs an instrumentation amplifier configuration that is highly effective in keeping external noisefrom affecting the signal transmission lines. Furthermore, the input stage is designed for high gain (22 dB)
and the power amplification stage for low gain (6 dB).
Consequently, the signal emerging from the signal input
section has a large amplitude which makes it much lessprone to external interference, thereby further improving
the noise performance.

Signal input section

Power amplification section

GAIN 22 dB

GAIN 6 dB+ INPUT+− INPUT−+■ Signal input section with high gain
Similar to the higher-ranked A-75, the signal input stage of
the A-48 is entirely configured with low-noise discrete
circuit components. This makes it possible to design thecircuit for a high gain of 22 dB (a multiplication factor ofapprox. 12.5), something that cannot be achieved with OPamp ICs. As a result, the S/N ratio of the amplifier is anastonishing 117 dB.

− INPUT

I-Vconverter

Current NFB
network

Buffer−OutputCurrent summing

Output6-parallel
power
amplifierGain control
circuitTrans-impedance amplifier
Buffer+ INPUT■ Principle of current feedback amplifier−+■ Instrumentation amplifier principle
Power amplification stage
with power MOS-FETs in
6-parallel push-pull
configuration

Signal input section■ Linear output characteristics over entire load

impedance range

The power amplification stage employs a 6-parallelpush-pull arrangement of power MOS-FETs mounted
directly to large heat sinks for highly efficient thermal
dissipation. The result is fully linear power progression of 45
watts into 8 ohms, 90 watts into 4 ohms, 180 watts into 2ohms, and 360 watts into 1 ohm (music signals). Plus, theimpressive damping factor of 800 means that the amplifier
can easily and competently drive any kind of loudspeaker.
Signal input section

GAIN 6 dB

400

MCS+(Multiple Circuit Summing)

Power MOS-FETs
in 6-parallel push-pull
configuration

350

Output power (W)GAIN 22 dB+B4+B3BIAS

BIAS+B2

INPUT

GND

MAX-3dB-6dB-12dB

DC SERVO+−BIAS＋−+B4−

250

194
180

10250

FEEDBACKNETWORK+B3OUTPUT

360

281

200

100-B3-B4GAIN
SELECTOR

300

150+B1BIAS+

438

450

Power amplification section

90Max. output power
Rated output power

45
8421

Impedance (Ohms)

BIAS-B2-B1■ Output power characteristics

BIAS

BIAS-B3-B4■ Circuit diagram of amplifier section (one channel)

Power MOS-FETs

Functionality ‒ Convenience that makes sense❶ Speaker output selector for
two pairs of speakers❶●❷●❸ Input selector button for
selecting the input signal❷ Meter display characteristics
selector❸●❹ Gain selector for changing
the amplification gain❹
●Advanced Features■ Power MOS-FETs in 6-parallel push-pull
configuration■ Linear output characteristics over entire load
impedance range■ Strong power supply with massive toroidaltransformer and large 60,000 μF filtering capacitors■ Instrumentation amplifier principle■ High-gain signal input section in discreteconfiguration■ Dedicated power supply for signal input section■ Line and balanced input connectors■ Polarity switching for balanced input connectors■ MCS+ circuit topology■ Current feedback principle in amplification circuitry■ Protection circuitry using MOS-FET switches■ High damping factor of 800■ Balanced Remote Sensing■ Speaker output protection circuit guards
against short-circuiting■ Highly responsive large peak powermeters■ Two sets of large speakerterminals■ 4-step gain control■ Support for bi-amping andbridged mode
■ Aluminum top plate withhairline finish

Large high-efficiency toroidal
power transformer

MOS-FET switches

60,000 μF filtering capacitors

Input signal and protection circuit board

Dedicated power supply for signal input section

Aluminum top platewith hairline finish

Bridged connection

Bi-amping connection

Fourfold output power for even more dynamic music reproduction

LRLR

Jumper wire

Right speaker

To LEFT
input

A-48 forright channel

Set to BRIDGE
on both units

LitLRLR

A-48 forleft channel

To LEFTinput

Left speaker

Jumper wire

Jumper wire

Right speaker

Jumper wire

Left speaker

For even higher definition by preventing interaction between low and high frequency range

A-48 forleft channel

To LEFT
input

LPreamplifier

Front PanelInput
selector button
LINE / BALANCED

Gain selector
MAX / −3 dB−6 dB / −12 dB

Function indicators
METER HOLD / BRIDGE / DUAL MONO /LINE / BALANCED

Guaranteed Specifications
Load8 ohms 4 ohms 2 ohms 1 ohm
Continuous Average
Normal / Bi-amping connection 45 W
90 W 180 W 360 W *1
Output Power(20 - 20,000 Hz)
Bridged connection
180 W 360 W 720 W *1 −LoadNormal / Bi-amping connection
Bridged connection

Intermodulation Distortion
S/N Ratio(A-weighted, with input shorted)

At rated continuous
average output

Gain

2 ohms0.05%−0.01%

4 to 16 ohms
0.03%
0.05%

Gain selector at MAX

117 dB

Gain selector at í12 dB

122 dB

Damping Factor
Frequency Response

Set to DUAL MONO
on both units

LitOperation mode selector

Dual mono connection
indicator

Rear Panel
Balanced inputconnectors

Power switch

Meter OFF button

Total HarmonicDistortion

A-48 forright channel

RBRIDGE indicator

Power meters

Speaker output selector
A / B / A+B

To LEFTinput

Preamplifier
Operation mode selector

Meter HOLD button

LR800
At rated continuous
average output

+] íG%

At 1 watt output
Selector position+] íG%MAX
íG%
í6 dB í12 dB

Normal / Bridged /Bi-amping connection

28.0 dB 25.0 dB 22.0 dB 16.0 dB

Line input connectors

AC power supply connector★
Balanced input
polarity selector

Speaker terminals A / B (2 sets)
Supported spadelug dimensions

Operation mode selector
DUAL MONO /NORMAL /BRIDGE

Min. 7 mm (0.28”)
Max.16 mm (0.63”)[Guaranteed specifications are measured according to EIA standard RS-490.]

Input Impedance
Output LoadImpedance

Balanced inputLine input
Normal / Bi-amping connection
Bridged connection

40 kilohms
20 kilohms
2 to 16 ohms * 2
4 to 16 ohms * 3

FormatLogarithmic scale,with indication off switch

Display rangeí to +3 dB(indication in dB and %)Power Meters

Hold time
In bridged modeSame indication for left and rightPower Requirements 120 V/220 V/230 V AC, 50/60 Hz (Voltage as indicated on rear panel)Idle
180 watts
Power Consumption
In accordance with IEC 60065
427 watts
Width465 mm (18.31”)
Maximum
Height211 mm (8.31”)
Dimensions
Depth464 mm (18.27”)
Net
33.0 kg (72.8 lbs)
Mass
In shipping carton
40.0 kg (88.2 lbs)

*1 With music signals only *2 1-ohm load permissible with music signals only *3 2-ohm load permissible with music signals onlyRemarks★ 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 230 V version has an Eco Mode that switches power off after 120 minutes of inactivity.
★ The shape of the plug of the supplied AC 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.
G1905Y PRINTED IN JAPAN 850-2215-00（B1）