● Pure Class A operation delivers 100 watts of quality power into 8 ohms ● Two totally identicalpower amplifier units driven in parallel ● 20-parallel push-pull arrangement of MOS-FET devices inoutput stage delivers linear high power progression to ultra-low 1-ohm impedance ● Input section
configured as dual instrumentation amplifier ● Double MCS+ circuit and current feedback topology inamplification stage ● Support for bridged use of two A-250 units for even higher output power● Strong power supply with massive high-efficiency toroidal transformer and large filtering capacitors

Witness a new dimension of musical expressiveness andbold presence

Ultra-low-noise design with unprecedented S/N ratio of 127 dB brings out a stunning wealthof detail. Semiconductor MOS-FET switches enable output circuitry without any mechanicalcontacts. Two pure class A power units arranged right and left are driven in parallel todeliver 100 watts into 8 ohms with impeccable quality. A damping factor in excess of 1,000
means that speaker control is nothing less than perfect. The massive A-250 represents a newpinnacle in power amplifier history. Encounter music like never before.

Technology development ahead of the curve■ Fully balanced signal paths realized with dual
instrumentation amplifier configuration
The A-250 features fully discrete circuit components ina dual configuration employing the latest instrumentation amplifier topology, allowing all signal paths
throughout the power amplifier to be fully balanced.
This not only eliminates any possible internal sourcesof noise or distortion as demonstrated by the outstanding performance ratings, it also makes the amplifier
highly impervious to changes in ambient conditions.
Consequently, operation stability and reliability which
are crucial for a power amplifier have been dramaticallyenhanced.

■ Double MCS+ (Multiple Circuit Summing) in amplifier stage realizes highest-ever signal/noise ratio inan Accuphase component
The Double MCS+ configuration uses four circuits for
amplifying the
input signal,
connected inparallel to keep
distortion to aminimum andto further
enhance S/Nratio and otherparameters.
The resulting
level of soundquality issimply stunning.

1,000– INPUT–NFBNETWORK+GAIN CONTROLCIRCUITOUTPUTCURRENT ADDER––CURRENT NFBNETWORKBUFFER+OUTPUT+ INPUT+– INPUTAMPLIFIER

CURRENT NFBNETWORKBUFFER

10-PARALLEL
POWER AMPNFBNETWORK+ INPUT

I -V
CONVERTER

BUFFER+–

10-PARALLEL
POWER AMPNFBNETWORK

I -V
CONVERTER

BUFFERAMPLIFIER■Current feedback principle assures excellent phase characteristics in high range
The current feedback topology developed by Accuphase isused for amplification. Since the impedance at the current
feedback point is very low, there is almost no phase shift, anda minimal amount of NFB results in maximum improvement ofcircuit parameters.

+GAIN CONTROLCIRCUIT––+

Phase selector for balanced
input provides support foreither pin 2 ⊕ or pin 3 ⊕systems.

■ Power amplifier assemblywith 10-parallel push-pull
power MOS-FET arrangement for output stage mounted directly to large diecast
aluminum heat sink, also
comprising the amplification
circuitry. Two completely
identical units are used.

Signal Input Stage GAIN 22 dB
GAIN < MAX, －3, －6, －12 dB >1,009W

Current Feedback Amplifier PrinciplePower Amplification Stage GAIN 6 dB

NFB
NETWORK■ Two totally identical power amplifier units driven inparallel
As shown in the circuit diagram of the amplifier section,
the power amplification stage makes use of twocompletely identical power units, each with 10 N-channel and 10 P-channel power MOS-FETs connected inparallel. These units are arranged on the left and rightside of the chassis and driven in parallel, resulting in a20-parallel configuration. This ensures a stablebalance in terms of electrical operation, weight distribution, thermal dissipation and other aspects. The parallel
drive approach achieves a total allowable power
dissipation value of 5.2 kW, which in turn reduces thepower load on each MOS-FET, allowing each device tooperate effectively in its range of optimum linearity.

Output power characteristics

Dual Instrumentation Amplifier Principle
Signal Input Stage GAIN 22 dB

Power Amplification Stage GAIN 6 dB
Double MCS＋（Multiple Circuit Summing）

Power MOS-FETs+ B2BIAS
STABILIZERCIRCUIT

900+ B3800+ B4＋
PREAMPLIFIER－Output power (W)700636W800WFEEDBACK
NETWORK＋BIAS
STABILIZERCIRCUITDCFEEDBACKAMP.

NFB
Network－600

BIAS
STABILIZERCIRCUITGAIN CONTROLCIRCUITBIAS
STABILIZERCIRCUITNFBNETWORK＋DCFEEDBACK
AMP.

500－

FEEDBACKNETWORK－400+ INPUT＋B3
NFB
NETWORK

400W

300200

B4PREAMPLIFIER

357W

＋BIAS
STABILIZERCIRCUIT

－B1

GND

191W

+ B1
NFB
NETWORKBIAS
STABILIZERCIRCUIT

200W

100

INPUT+ B3＋PREAMPLIFIER－100W

Max. output power

FEEDBACKNETWORK

Rated output power8Ω4Ω2Ω1Ω
Impedance (Ohms)

OUTPUTGND+ B4＋DC
FEEDBACKAMP.

－BIAS
STABILIZERCIRCUITGAIN CONTROLCIRCUIT＋NFB
NetworkDC
FEEDBACKAMP.

－FEEDBACKNETWORKBIASSTABILIZERCIRCUITNFBNETWORKBIAS
STABILIZERCIRCUIT－PREAMPLIFIER＋B4B3BIAS
STABILIZERCIRCUIT

Power MOS-FETs

B1Circuit diagram of amplifier section

The Pinnacle of Technology

The Beauty of Tradition

Ultra-massive pure Class A monophonicpower amplifier
A-250 is built to excel in every respect. Carefully
selected exquisite parts and materials are brought
together to realize leading-edge technology.
Enclosed by the refined champagne gold faceplate
and a massive top plate cut from ultra-thick aluminum with a beautiful hairline finish, the amplifier
exudes an atmosphere of solid elegance anddependable power.

Advanced Features■ 20-parallel push-pull arrangement of power MOS-FETs delivers linear
power progression: 800 watts (music signal) into 1 ohm, 400 watts into
2 ohms, 200 watts into 4 ohms, or 100 watts into 8 ohms.
■ Strong power supply with massive high-efficiency toroidal transformer
and two large 100,000 µF filtering capacitors.
■ Printed circuit boards in power amplifier assembly made from glass cloth
fluorocarbon resin with low dielectric constant and minimum loss.
■ 4-stage gain selector (MAX, –3 dB, –6 dB, –12 dB) also minimizes residual noise.
■ Two sets of oversize speaker terminals accept also spade lugs andbanana plugs and allow bi-wiring connection.
■ Semiconductor (MOS-FET) switches used for protection circuitry prevent
contact problems and ensure long-term reliability. Eliminating mechanicalcontacts from the signal path also further enhances sound quality.
■ Fully balanced input stage shuts out external noise interference.

■ OPERATION selector allows use of two A-250 units for bi-amping orbridged operation. Bridging allows upgrade to monophonic amplifier witheven higher power, delivering 1,600 watts into 2 ohms (music signal), 800
watts into 4 ohms, or 400 watts into 8 ohms.
■ Output level indication switchable between 5-digit numeric readout and40-point LED bar graph with further improved readability. Hold time selector
button also provided.
● Meter operation on/off switch.
● Digital power meter showing
true power values, based on
output current detected by aHall element.
Digital power meter/bar graph meter● Power meter range selector and auto range function for automatic power tracking.
■ Major parts in power supply and signal path are gold-plated.

-toLarge high-efficiency
toroidal power transformer

100,000 μF filtering capacitors

Large gold-plated speaker terminal made of solid brass

Top plate with hairline finish

Gain control selector

MOS-FET switches

Balanced amplifier assembly

Ultra-heavy-gauge edgewise coil

Digital power meter range selector / Hold time selector buttonProtection circuit assembly

OPERATION selector

Gold-plated parts

■ Using four A-250 units, bridged operation or bi-amping is possible.

■ Connect the input signal either to the balanced or the unbalanced inputs.

Example for bridged connection
Bridged operation of two A-250 units allows upgrading to amonophonic amplifier with even higher power.
＊ For connecting the SPEAKER － terminals to each other,use speaker cable－of the same grade as for other speakerconnections.
＊ OPERATION selector of left channel/right channel ❶ unit:
BRIDGE NOR＊ OPERATION selector of left channel/right channel ❷ unit:
BRIDGE REV.
Branch output

To LINE "1" input

LTo BALANCED "1" input

LR
To LINE "1" input－Example for bi-amping connection

Left speaker＋＋

Right speaker－＋－

Left-channel unit ❷To LINE "1" input

L

To BALANCED "1" input

LR
To LINE "1" input

To BALANCED "1" input

Branch output

Branch output＋

PreamplifierR－＋－

Right-channel unit ❶＋Hold time indicator
1 SEC / ∞＋－＋ －＋＋Left-channel unit ❷Left-channelunit ❶Branch output－＋－＋

Right-channel unit ❷Right-channel unit ❶Line inputs

Button for opening
the sub panel

Hold time
selector button－－

HIGH LOW

Rear panel
Input type indicator
LINE / BALANCEDPower switch＋Preamplifier

RFront panel

Meter selector
OFF / ALL / dB / W Sub panel
Digital power meter
range selector
AUTO / 10W / 100W / 1000W＋ －－Right speaker

To BALANCED "1" input

Right-channel unit ❷Digital power meter
Bar graph meter

Left speaker

HIGH LOW－Left-channelunit ❶In 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.
＊ The speakers must－have a built-in crossover network andseparate inputs for LOW and HIGH range.
＊ Set the OPERATION selectors of all four units toNORMAL.

Gain selector–12dB / –6dB /–3dB / MAX
Input selector button

Balanced inputs② Inverted (–) ③ Non-inverted (+)(Can be changed with phaseselector switch)

OPERATION selector
NORMAL / BRIDGE NOR. /BRIDGE REV.

Speaker terminals

AC power connector ★

Balanced input
phase selector switch

Guaranteed Specifications [Guaranteed specifications are measured according to EIA standard RS-490.]
Notes: (＊1) Ratings marked ＊1 are forContinuous Average Output Power (20 - 20,000 Hz)
music signals only.
Normal mode
800 watts into 1 ohm ＊1(＊2) The output range for pure class
400 watts into 2 ohms
A operation is 100 W.
200 watts into 4 ohms
100 watts into 8 ohms ＊2
Bridged mode (2 units) 1,600 watts into 2 ohms ＊1
800 watts into 4 ohms
400 watts into 8 ohms

Total Harmonic Distortion 0.05%
0.03%

Input Impedance

Balanced:Line:

Signal-to-Noise Ratio(A-weighted, with inputshorted)

127 dB (GAIN selector in MAX position)
133 dB (GAIN selector in –12 dB position)
At rated continuous average output

Output Level Meter

Digital power meter5-digit indication showing true power (W)Range selection AUTO / 10 W / 100 W / 1,000 W
Bar graph meter
Represents output voltage values (dB) using 40 points
Peak hold time
1 second / ∞ (infinite) selectable＊Display off switch provided

with a 2-ohm loadwith a 4 to 16-ohm load

Intermodulation Distortion 0.01%Frequency Response

At rated continuous average output: 20 - 20,000Hz ＋0 －0.2 dB
At 1 watt output:
0.5 - 160,000Hz ＋0 －3.0 dB

Gain

28.0 dB (GAIN selector in MAX position)

Gain Selection

MAX, –3 dB, –6 dB, –12 dB

Output Load Impedance Continuous output: 2 to 16 ohms
With music signal: 1 to 16 ohms
Damping Factor

1,000

Input Sensitivity(with 8-ohm load)

1.13 V for rated continuous average output
0.11 V for 1 watt output

40 kilohms
20 kilohms

Power Requirements

120/220/230 V AC, 50/60 HzPower Consumption

300 watts idle
430 watts in accordance with IEC 60065

Maximum Dimensions Width 465 mm (18.31)
Height 238 mm (9.37)
Depth 514 mm (20.24)
Mass

46.0 kg (101.4 lbs) net
55.0 kg (121.3 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.
★ The 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 accessories
AC power cord

The specifications and appearance of this product are subject to change without notice.
E1705Y PRINTED IN JAPAN 850-2203-00（B1）