Class-A

MONOPHONIC POWER AMPLIFIER● Class A driven output stage with 20-parallel push-pull power MOS-FETs ● Largelinear output 125 W / 8 ohms, 250 W / 4 ohms, 500 W / 2 ohms, 1,000 W / 1 ohm● Instrumentation amplifier principle ● Current feedback amplification circuits● Balanced Remote Sensing ● Double MCS+ circuit ● High damping factor of 1,000● Speaker output protection ● Highly responsive large-scale bar graph power meter● Connecting two pairs of A-300 supports bi-amping and bridged mode connectionAccuphase’s 50th Anniversary model embodies power amplifier perfection
Created to mark our 50th anniversary, the A-300 redefines the ideal for Class A power amplifiers. 20-parallel push-pull power
MOS-FETs in the output stage improves performance by 25% over conventional models with outputs of 125 W into 8 ohms, 250 W
into 4 ohms, 500 W into 2 ohms, and 1,000 W into 1 ohm that set the stage for enviable constant-voltage drive. The fully discretebalanced input amplifier achieves a level of quietness that will make you forget you are using audio equipment for reproduction.
The A-300’s unmatched expressiveness lets you enjoy the most exquisite pieces from the world’s greatest composers.

Groundbreaking technology
The A-300 employs sophisticated circuitry and hand-selected materials to create a power amplifier with well-honed expressiveness and cutting-edge technologies.
■ Ample output power

Balanced remote sensing improves damping
factor by feeding back the GND at the sametime as the signal output from speaker terminals.
Signalfeedback■ Ultra low noise performance＋Ideal gain distribution and other sophisticatedtechniques improve noise level suppression by
20% over conventional models.
20% improvement
A-300

10μV

Conventionalmodels

12.6μV−GNDfeedback■ Ideal gain distribution
Noise level suppression has been dramatically improvedby assigning a high gain (12.6×) in the signal input
section with excellent noise figure results.

Input

12.6×

2×–+Output
signal––Output−+Signalinput section

Signal input section+ B1+ INPUT+ B2+ B3

−

Input

I-V
converter

BufferCurrent
summing

OutputCurrent NFB
network

BufferPoweramplification section

ProtectionSignalcircuit section input section+ B4

Filtering capacitors- B2+ B1+ B2- B1−+ B2- B2+ B1Transformer impedanceSpeakerterminals

Power amplification stage+ B2

The current feedback amplification circuit offers excellent phasecharacteristics in the high-frequency range with almost no
impact on the frequency response even when gain is switched,resulting in natural and dynamic driving of the speakers.

- B2- B1

- B1＋

Power amplification section
Voltage amplification stage

2-parallel circuit layout of MCS+ principle＋- B3- B4OUTPUTGNDGND- INPUT

Output■ Current feedback amplification topology+＋SignalPowerinput section amplification section

- B1＋
Input
−Speakerterminals

With balanced circuits in the signal input
section, the amplification stage is comprised
entirely of an instrumentation amplifier
principle that equalizes input impedance on
the + and – sides, for excellent external
noise suppression, and providing optimal
circuitry for this high-end audio amplifier.

Input‑+ B1＋

GND sensing point(closest speaker terminal)

MCS+ circuitry

With a damping factor of 1,000, the speakers can bedriven with full control over the counter-electromotive
forces to get the most out of your speakers.

+2-parallelcircuit−■ High damping factor

Transmission signal

Signal sensing point(closest speaker terminal)Poweramplification

Input

By placing the voltage amplification stage in a
two-parallel circuit layout, the MCS+ (Multiple Circuit
Summing-up) circuit theoretically reduces the noise
floor by about 30%. The A-300 comes with 2 MCS+
circuits in a Double MCS+ circuit configuration.

■ Instrumentation amplifier

Noise levelInputsignal■ Double MCS+ circuit■ Balanced remote sensing

The Class A driven 20-parallel push-pull power MOS-FETs
in the output stage produce linear output power of 125 W
into 8 ohms, 250 W into 4 ohms, 500 W into 2 ohms, and atremendous 1,000 W into 1 ohm of maximum output power.

+ B2+ B3+ B4- B2- B3- B4- B2+ B2- B2Circuit diagram

Poweramplification section

Toroidaltransformer

Poweramplification sectionImpeccably Styled

Impeccable SoundAdvanced features■ Class A driven 20-parallel push-pull MOS-FET output stage■ 125 W into 8 ohms, 250 W into 4 ohms, 500 W into 2 ohms, and1,000 W into 1 ohm large linear output power■ Instrumentation amplifier■ Current feedback amplification topology■ Balanced remote sensing■ Double MCS+ circuitry■ High damping factor of 1,000■ Meter display switching ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・①■ Digital power meter display range switching ・・・・・・・・・・・・・・・・・・・②■ Hold time switching function that changes
the meter peak display time ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・③■ LINE / BALANCED input switching・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・④■ 4-step gain control・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑤■ Polarity switching of balanced input connectors ・・・・・・・・・・・・・・⑥■ Bridge connection switching・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑦■ Signal input section with a fully discrete configuration
for low noise ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑧■ Speaker output protection circuit guards against
short-circuiting ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑨■ Large speaker terminals connected directly toprotection circuitry・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑩■ Edgewise coils improve damping factor ・・・・・・・・・・・・・・・・・・・・・・・・⑪■ Highly reliable MOS-FET switches withno mechanical connections ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑫■ Large, high-efficiency toroidal transformer ・・・・・・・・・・・・・・・・・・・・・⑬■ High capacity 100,000 μF filtering capacitors・・・・・・・・・・・・・・・・・・・⑭■ Aluminum hairline finish top plate ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑮■ Highly responsive large-scale bar graph meter anddigital power meter・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑯■ High-carbon cast iron insulator feet withsuperior damping characteristics ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑰■ Power amplification section on circuit boards using
glass cloth fluorocarbon resin ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・⑱

Sub Panel

Rear Panel① Meter display ② Meter display ③ Hold time ④ Input

selector

range selector

selector

selector

selector⑧ Signal input section⑥ Balanced

input polarity
selector⑦ Operation mode

selector⑨ Protection circuit section⑩ Speaker terminals⑪ Edgewise coil

⑫ MOS-FET switches⑬ Toroidal transformer⑭ Filtering capacitors⑮ Top plate⑯ Power meter⑱ Power amplification section⑤ Gain⑰ Insulator feetBi-amping Connection (High quality performance eliminates interaction between high and low ranges)

Bridged connection (4× greater power output)
L Speaker

R Speaker

L Speaker

Jumperconnection

Connection
with a hi-grade
speaker cable

Uses A-300 L

R Speaker

Jumpers
removedJumperconnection

Jumpers
removedConnection
with a hi-grade
speaker cable

Uses A-300 L

Uses A-300 RLRUses A-300 R

Uses A-300
L LOW

Uses A-300
L HIGH＊ Set the operation mode
selector to BRIDGE NOR.
to use A-300 L/A-300 RL＊ Set the operation mode
selector to BRIDGE REV.
to use A-300 L/A-300 R

Uses A-300
RL LOW＊ Requires speaker systemwith HIGH and LOW terminals.

R＊ Set the operation mode
selector to NORMAL whenusing 4 A-300s

Preamplifier

Preamplifier

Front Panel

Rear Panel

Meter hold time
indicator

Bar graph meter
Digital power meter

Sub panelPower switch

Input indicators

Button for opening
the sub panel* See the previous page for information on the controls in the sub panel.

Input terminals(LINE / BALANCED)

Uses A-300
R HIGH

Supported spade lug dimensions
Speaker terminals
Min.
Max.
(Upper and lower terminals
6.3 mm 19 mm
normally output the same signal)

Operationmode selector

Balanced
input polarity selector

AC power
supply connector

Guaranteed Specifications
Load
8 ohms 4 ohms 2 ohms 1 ohm
Rated Output
Normal / bi-amping connection 125 W 250 W＊1 500 W＊1 1,000W＊1(20 – 20,000 Hz,0.05%)
Bridged connection
500 W＊1 1,000 W＊1 2,000 W＊1ー2 ohms
0.05%
Normal / bi-amping
Total HarmonicconnectionDistortion
4 to 16 ohms
0.03%
(20 – 20,000 Hz)
Bridged connection
4 to 16 ohms
0.05%Intermodulation Distortion
0.01%
At rated output
20 – 20,000 Hz (+0, –0.2 dB)
Frequency Response
0.5 – 160,000 Hz (+0, –3.0 dB)
At 1 W output
Damping Factor
1,000 or greater
Input Impedance
BALANCED / LINE input
40 kilohms / 20 kilohms
At rated output
At 1 W output
OutputInput Sensitivity
Normal / bi-amping connection
1.26 V
0.11 V
Bridged connection
1.26 V
0.056 V
Signal-to-Noise Ratio(A-weighted, input shorted)

Gain switch at
MAX / –12 dB

130 dB / 135 dB

Gain
Power Meter
PowerRequirements

Gain switch
MAXíG%íG% íG%
Normal / bi-amping connection 28 dB
25 dB
22 dB
16 dB
Logarithmic scale, with illumination off switch
FormatDisplay range
í∞ ~ +3 dB
Hold time
1 sec. / ∞ switchable
120/220/230 V AC, 50/60 Hz(Voltage as indicated on rear panel)PowerConsumption

Idle
In accordance with IEC 62368-1
Stand-by

MaximumDimensions

Width 465 mm (18.3”) × Height 240 mm (9.4”) × Depth 515 mm (20.3”)

Mass230 W
270 W
0.3 W

Net
In shipping carton

46.0 kg (101.4 lbs)
55 kg (122 lbs)

“Normal connection” indicates standard operation.
＊1: Limited to music signals

Supplied accessories● AC power cordRemarks★ 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.

●The specifications and appearance of this product are subject to change without notice.

https://www.accuphase.com/

K2204Y

850-2234-00（B1） PRINTED IN JAPAN