m Pure Class A operation delivers quality power: 30 watts × 2 into 8 ohmsm Power MOS-FET output stage features triple parallel push-pull
configuration m Instrumentation amplifier principle m Further improved MCS+
circuit topology m Current feedback combines operation stability withoutstanding sound m Bridged mode allows upgrading to true monophonicamplifier m Massive transformer rated for 400 VA m 4-step gain control

Pure Class A power amplifier using power MOS-FET devices Fullybalanced signal paths as found in high-quality instrumentation
amplifiers. Further refined MCS+ topology and current feedback design
result in even better S/N ratio, distortion, and other performanceparameters. Robust power supply and power MOS-FET devices in triple
parallel push-pull configuration sustain an amazing 150 watts perchannel into ultra-low 1-ohm impedance loads (with music signals).
amplifier is running hot. Driving these devices inpure class A assures high-definition sound thatbrings out the finest nuances in the music.
In pure class A operation, the power supply delivers
a steady current, regardless of the presence orabsence of a musical signal. This means that theamplifier remains unaffected by fluctuations involtage and other external influences. On the otherhand, it also means that the output stage generates
considerable thermal energy. In the A-30, this isdissipated effectively by large heat sinks which
provide ample capacity to remove the heatproduced by the internal circuitry.
The heavy-duty power supply easily sustains
output levels of 120 watts into 2 ohms, 60 watts
into 4 ohms, or 30 watts into 8 ohms (per channel).
This linear progression demonstrates that theamplifier will be capable to drive even speakers
with very low impedance ratings or withpronounced impedance fluctuations. Stability
remains excellent at all times. The amplifier also
has the necessary reserves to handle musicaltransients that require considerable power in aninstant. If even higher power is required, bridged
mode turns the A-30 into a high-output
monophonic power amp.

Pure Class A power amplifiers from Accuphasehave long been blending the purity of class A
operation with the superior performance of power
MOS-FETs. While building a string of outstandingamplifiers, Accuphase has accumulated a storeof technical know-how that is second to none. The
latest in this series, the A-30 is a pure class A
stereo power amplifier based on the advanced
technology of the model A-60.
The A-30 employs the so-called instrumentation
amplifier principle throughout. The signal handlingstages feature further improved MCS+ topology
and the renowned current feedback approach. This
has resulted in electrical characteristics that
surpass even the demanding standards set by its
predecessors. Employing only highest gradematerials and strictly selected parts, the A-30
pursues the two most important goals of anamplifier: very low output impedance (Note 1) andconstant drive voltage (Note 2).
The output stage of the A-30 features power MOSFET devices renowned for their excellent soundand superior reliability. Because they have negative
thermal characteristics, there is no danger ofthermal “runaway” as exists with bipolar transistors.
Operation remains totally stable even when theInstrumentation amp configuration allows fullybalanced signal paths
The A-30 features a new “instrumentation amplifier”
principle whereby all signal paths from the inputs tothe power amp stage are fully balanced. This results
Signal input stage

Power amplifier stage++ INPUT–NFBNETWORK+–GAIN CONTROLCIRCUITOUTPUTNFBNETWORK–+– INPUT

Instrumentation amplifier configurationin excellent CMRR (Common Mode Rejection Ratio)
and minimal distortion. Another significant advantage
is that external noise and other external influences
are vir tually shut out. The result is a drastic
improvement in operation stability and reliability.
Further refined MCS+ topology for even lower
noise

Low amplifier output impedance

The load of a power amplifier, namely the loudspeaker, generates a
counterelectromotive force that can flow back into the amplifier via theNF loop. This phenomenon is influenced by fluctuations in speaker
impedance and interferes with the drive performance of the amplifier.
The output impedance of a power amplifier should therefore be madeas low as possible by using output devices with high current capability.
This absorbs the counterelectromotive force generated by the voice coiland prevents the occurrence of intermodulation distortion.

Note 2:

Constant drive voltage principle

Even in the presence of a load with wildly fluctuating impedance, theideal power amplifier should deliver a constant voltage signal to theload. Figure 2 shows the results of actual output voltage/output current
measurements at different load impedances for the A-30. It can be clearlyseen that output voltage is virtually constant at various loads, whichmeans that current increases in a linear fashion. Actual measurementsof clipping power have yielded the following figures, which impressively
demonstrate the more than ample performance of the A-30: 1 ohm: 175
watts, 2 ohms: 142 watts, 4 ohms: 94 watts, 8 ohms: 58 watts.

Accuphase's original MCS (Multiple Circuit Summing)

Output current (A)Note 1:principle uses a number of identical circuits
connected in parallel to achieve superior performance
characteristics. MCS+ is a further refined version ofthis approach. Improvements in the bias circuitry of
the input-stage buffer amplifier result in greater
stability. This in tur n makes it
possible to extend the parallel
operation approach to the class A
drive stage of the current/voltage
converter, thereby further lowering
the noise floor.

Output voltage (V)★1-ohm rating is for music signals only.

Fig. 2 Load impedance vs. output power(Output voltage/output current)

MCS+Circuit( MultipleSumming )+ B3

Bias stabilizer
circuit+ B1

REGULATOR

Q1
Q5

Q9

Q 13

Q7

Q 11

Q 15+ B2
Q 17+ INPUT

+–Q3

NFB
NETWORK

Q 19

Q 21

Q 23

Q 25

Bias stabilizer
circuitNFB
NETWORKGAIN CONTROLCIRCUIT
Bias stabilizercircuit

OUTPUT

Bias stabilizer
circuitNFB
NETWORKQ2– INPUT–+Q6

Q 10Q 14Q8Q 12Q 16Q 18Q 20Q 22Q 24

Q 26– B2Q4

REGULATOR– B1– B3
Bias stabilizer
circuitFig. 1 Circuit diagram of amplifier section (one channel)

Power MOS-FET output stage
with triple parallel push-pull
power units delivers 120 watts
into 2 ohms, 60 watts into 4 ohms,
or 30 watts into 8 ohms withoutstanding linearity
The output stage (Figure 1) uses
power MOS-FETs. Three pairs ofthese devices are arranged in aparallel push-pull configuration foreach channel. The result is stable
operation with ideal power linearity
even down to ultra-low impedances.
The maximum power dissipation of
one MOS-FET is 130 watts, but theactual power load per pair is much

Gain

(Large)coupled withutterly naturale n e r g yb a l a n c e.
Figure 4 shows
frequency
response for(High)
Frequency
different gain
Fig. 4 Frequency response with current feedback(Response remains uniform also when gain changes)
settings of thec u r r e n t
feedback amplifier. The graphs demonstrate that
response remains uniform over a wide range.

lower, so that each device is driven only in its lowpower range where linearity is excellent.
A music signal consists of a continuous successionof pulse waveforms. To prevent clipping on occasional
momentary high-level pulses, the maximum clippinglevel of the A-30 is set to 50 watts per channel into 8ohms (sine wave output).
Current feedback circuit topology assures
excellent phase characteristics in high range
In the A-30, the signal current rather than the moreconventionally used voltage is used for feedback.
Since the impedance at the current feedback point(current adder in Figure 3) is very low, there is almost– Input
Buffer+ Input
BufferCurrent
adder
I-V
converter

OutputAmplifierTrans-impedance
amplifierCurrent NFB
networkFig. 3 Principle of current feedback amplifierno phase shift. Phase compensation
therefore can be kept at aminimum. A minimal amount ofNFB results in maximum
improvement of circuit
parameters. The result isexcellent
transient
response and superb
sonic transparency,Robust power supply with large powertransformer and high filtering capacity
In any amplifier, the power supply plays a vital rolesince it acts as the original source for the output
delivered to the speaker. The A-30 employs a large
and highly efficient 400 VA power transformer. It ishoused in an
enclosure filled witha material thattransmits heat andabsorbs vibrations.
This completely
preventsany
adverse influenceson other circuit
parts.
Twoaluminumelectrolytic
capacitors rated for
47,000 µF eachserve to smooth out
the pulsating direct
current from therectifier, providing
more than ample
filtering capacity.

n Power amplifier assembly with threeparallel push-pull power MOS-FET
pairs per channel mounted directly
to large heat sink, MCS+ circuitry,
and current feedback amplifier

Instrumentation amp type gain control minimizes
residual noisen Easy switching between dual mono/stereo/bridgedmode
In the dual mono position of themode selector, the left-channel
signal is supplied to both speakerterminals, which can be used for biamping with dedicated low-range
and high-range drivers.

The gain control switches gain in the first amplification
stage that uses aninstrumentation ampdesign. Four settings areavailable (MAX, –3 dB,–6 dB, –12 dB). With thisapproach, reducing gain
also results in reduced
noise. This is especiallybeneficial when using highly efficient speakersystems where the noise floor could be a problem.

n Oversize speaker terminals also accept Y lugs andbanana plugs

Unbalanced and balanced input connectors

The sturdy terminals canhandle even very large
gauge speaker cable.
The connectors are
made of extruded highpurity brass material andare gold-plated for utmost reliability and minimum contact resistance.
Y lugs and banana plugs can also be used.

Bridged connection allows upgrading to a truemonophonic amplifier with 300 watts into 2 ohms
(music signals only), 240 watts into 4 ohms, and120 watts into 8 ohms

Protection and meter circuit assemblyn Large analog power metersn Balanced connection prevents induced noisen PCB copper foil and all major signal path components
are gold-plated

Operation in bridged mode results in a monophonicamplifier with four times the power output than during
stereo operation. This gives effortless dynamicpower.

n Buttons for meter on/off, meter sensitivity, and input
selection

High-quality, high-reliability parts

n Front panel

GUARANTEED SPECIFICATIONS[Guaranteed specifications are measured according to EIA standard RS-490.]m Continuous Average Output Power (20 - 20,000 Hz)
Stereo operation
150 watts per channel into 1 ohm (✽)(both channels driven)
120 watts per channel into 2 ohms
60 watts per channel into 4 ohms
30 watts per channel into 8 ohms
Monophonic operation(bridged connection)

300 watts into 2 ohms (✽)
240 watts into 4 ohms
120 watts into 8 ohms

Note: Load ratings marked (✽) apply only to operation with music signals.
m Total Harmonic Distortionn Rear panel

Stereo operation (both channels driven)
0.05%, with 2-ohm load
0.03%, with 4 to 16-ohm load
Monophonic operation (bridged connection)
0.05%, with 4 to 16-ohm loadm Intermodulation Distortion 0.005%
m Frequency Response

At rated output:
At 1 watt output:

m Gain28.0 dB (GAIN selector in MAX position)(stereo and monophonic operation)

m Gain Settings

MAX, –3 dB, –6 dB, –12 dB

m Output Load Impedance

Stereo operation:
2 to 16 ohms
Monophonic operation: 4 to 16 ohms

20 ~ 20,000 Hz +0, –0.2 dB
0.5 ~ 160,000 Hz +0, –3.0 dB[★ With music signals, load impedances of 1 Ω (stereo) or 2 Ω (mono) can be driven.]m Damping Factor★
★
A Right/left-channel output power meters (dB and % scale)
B Function indicators

H Unbalanced inputs
I Balanced inputs

METER, –20 dB, UNBALANCED, BALANCED, BRIDGEC Meter operation/illumination switch
ON OFFD Meter sensitivity selector button (–20 dB)
E Input selector button UNBALANCED BALANCED
F Power switch
G Gain selector

a: Groundb: Inverted (–)
c: Non-inverted (+)
J Mode selector
DUAL MONONORMALBRIDGE
K Right/left-channel speaker output terminals
L AC power supply connector★

MAX

–3 dB

–6 dB

–12 dB

Remarks★ This product is available in versions for 120/230 V AC. Make sure that the voltage shown on therear panel matches the AC line voltage in your area.
★ The shape of the AC inlet and plug of the supplied power cord depends on the voltage rating anddestination country.

n Supplied accessories:

150m Input Sensitivity (with 8-ohm load, GAIN selector in MAX position)
Stereo operation:
0.57 V for rated continuous average output of 30 W
0.11 V for 1 watt output
Monophonic operation: 1.14 V for rated continuous average output of 120 W
0.11 V for 1 watt output
m Input Impedance

Balanced: 40 kilohms

m Signal-to-Noise Ratio(A-weighted, input shorted)

111 dB (GAIN selector in MAX position)
118 dB (GAIN selector in –12 dB position) at rated output

m Output Level Meters–40 dB to +3 dB (dB/% scale)
Logarithmic scale, with switching capability for meter operation and sensitivity

Unbalanced: 20 kilohms

m Power Requirements

AC 120 V/230 V (Voltage as indicated on rear panel) 50/60 Hz

m Power Consumption

170 watts idle
260 watts accordance with IEC 60065

m Maximum Dimensions

Width 465 mm
Height 170 mm
Depth 425 mm

m Mass21.5 kg (47.4 lbs) net
26.0 kg (57.3 lbs) in shipping carton(18-5/16”)(6-11/16”)(16-3/4”)• AC power cord

• Specifications and design subject to change without notice for improvements.

http://www.accuphase.com/

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