Accuphase A-45

Accuphase A-45 – Class-A Stereo Power Amplifier – Mint Condition – Original Packaging

The Accuphase A-45 represents a particularly impressive generation of the Japanese manufacturer's pure Class-A power amplifiers. Delivering 45 watts per channel into 8 ohms, it combines a sophisticated MOS-FET output stage with fully balanced signal paths and an exceptionally substantial power supply.

Within the Accuphase range of its era, the A-45 was positioned between the A-30 and A-60 – designed for systems requiring greater reserves than the A-30 without necessarily requiring the output capability of the larger A-60.

The example offered here is exceptional. It has survived in virtually new mint condition and retains its original Accuphase shipping carton, original packing materials, protective sleeve and original supplied accessories.

Pure Class-A Operation

At the heart of the A-45 is a true Class-A output stage using six parallel pairs of power MOS-FETs per channel in push-pull configuration.

Rated output is 45 watts per channel into 8 ohms, but the amplifier's ability to deliver power into progressively lower impedances reveals the considerable reserves behind that figure:

• 45 W + 45 W into 8 ohms
• 90 W + 90 W into 4 ohms
• 180 W + 180 W into 2 ohms
• up to 360 W + 360 W into 1 ohm with music signals

This near doubling of output as load impedance is halved demonstrates the remarkable current capability of the A-45.

Six Parallel MOS-FET Pairs per Channel

Accuphase employs six parallel pairs of power MOS-FETs in each channel. The output devices are mounted directly to the substantial external heatsinks required by the permanently high dissipation of true Class-A operation.

With its imposing heatsinks, extremely robust construction and a net weight of 30.9 kg, the A-45 is a physical expression of the engineering involved.

Fully Balanced Instrumentation Amplifier Topology

The A-45 employs Accuphase's instrumentation amplifier principle, maintaining fully balanced signal paths from the inputs through to the power amplifier stage.

The design is intended to provide excellent common-mode rejection, very low distortion and a high degree of immunity to external interference.

Accuphase also employs its refined MCS+ – Multiple Circuit Summing – architecture, in which multiple identical circuits operate in parallel to further reduce inherent noise.

Current Feedback

Another important element of the A-45 is Accuphase's current-feedback topology.

Instead of using signal voltage for feedback, the circuit employs signal current. The very low impedance at the feedback point results in minimal phase shift, particularly at high frequencies, allowing excellent circuit performance with relatively little negative feedback.

Together, the instrumentation amplifier topology, MCS+ architecture and current-feedback design form the technological foundation of the A-45.

A Formidable Power Supply

Pure Class-A operation places considerable demands on a power supply, and Accuphase designed the A-45 accordingly.

A high-efficiency 600 VA toroidal transformer is combined with two massive 47,000 µF filter capacitors, providing a total of 94,000 µF of reservoir capacitance.

The scale of this power supply helps explain the amplifier's ability to maintain substantial output even into extremely demanding low-impedance loads.

Stereo, Dual Mono and Bridged Operation

The A-45 can operate in Stereo, Dual Mono or Bridge mode.

In bridged configuration, a single A-45 becomes a powerful mono amplifier capable of:

• 180 W into 8 ohms
• 360 W into 4 ohms
• up to 720 W into 2 ohms with music signals

Four selectable gain settings – MAX, −3 dB, −6 dB and −12 dB – allow the amplifier to be optimally matched to the preamplifier and overall system while helping minimise residual noise in highly sensitive installations.

Classic Accuphase Design

Visually, the A-45 is unmistakably Accuphase.

Its champagne-gold front panel is dominated by two large analogue power meters. Meter sensitivity can be increased by 20 dB, while both meter operation and illumination can be switched off when desired.

Balanced XLR and unbalanced RCA inputs, together with substantial loudspeaker terminals, complete the amplifier's comprehensive specification.

Technical Specifications

• Type: Pure Class-A stereo power amplifier
• Output stage: 6 parallel MOS-FET pairs per channel
• Stereo output: 45 W/ch into 8 Ω
• Stereo output: 90 W/ch into 4 Ω
• Stereo output: 180 W/ch into 2 Ω
• Stereo output: up to 360 W/ch into 1 Ω with music signals
• Bridged output: 180 W into 8 Ω
• Bridged output: 360 W into 4 Ω
• Bridged output: up to 720 W into 2 Ω with music signals
• THD: 0.03 % into 4–16 Ω
• Intermodulation distortion: 0.004 %
• Frequency response at rated output: 20 Hz–20 kHz, +0/−0.2 dB
• Frequency response at 1 W: 0.5 Hz–160 kHz, +0/−3 dB
• Gain: 28 dB
• Gain settings: MAX / −3 / −6 / −12 dB
• Damping factor: 200
• Signal-to-noise ratio: 115 dB at MAX gain, up to 120 dB at −12 dB
• Balanced input impedance: 40 kΩ
• Unbalanced input impedance: 20 kΩ
• Power transformer: 600 VA toroidal
• Filter capacitance: 2 × 47,000 µF
• Dimensions: 465 × 211 × 464 mm
• Net weight: 30.9 kg

Condition and Completeness

This particular A-45 is in exceptionally well-preserved condition. The front panel, controls and cabinet present themselves in virtually new condition.

Equally remarkable is its completeness. The original Accuphase shipping carton, original internal packing materials and protective sleeve have all been preserved, together with the original supplied accessories.

Finding an A-45 preserved to this standard and with such complete original packaging has become increasingly uncommon.

Our Verdict

The A-45 is a superb example of why Accuphase Class-A power amplifiers enjoy such an enduring reputation. Its nominal 45 watts per channel tell only a small part of the story.

Six parallel MOS-FET pairs per channel, fully balanced signal paths, MCS+, current feedback and a 600 VA power supply with 94,000 µF of reservoir capacitance demonstrate the extraordinary engineering behind this amplifier.

This particular example combines that engineering with equally exceptional preservation. Virtually new, highly complete and supplied in its original Accuphase packaging, it is an outstanding proposition both for the serious music lover and the dedicated Accuphase collector.