Accuphase A 45 Brochure
User Manual: Accuphase-A-45-Brochure
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m Pure Class A operation delivers quality power: 45 watts × 2 into 8 ohms m Power MOS-FET output stage features 6-parallel push-pull configuration m Instrumentation amplifier principle m Further improved MCS+ circuit topology m Current feedback combines stable operation with outstanding sound m Bridged mode allows upgrading to true monophonic amplifier m Large high-efficiency toroidal transformer rated for 600 VA m 4-step gain control Pure Class A power amplifier uses power MOS-FET devices to deliver 45 watts per channel (8 ohms) – Fully balanced signal paths as found in highquality instrumentation amplifiers. Further refined MCS+ topology and current feedback result in superb sound quality and excellent ratings for S/N ratio, THD, and other parameters. Strong power supply and power MOSFET devices in six-parallel push-pull configuration sustain an amazing 360 watts per channel into ultra-low impedance 1-ohm loads (with music signals). Pure Class A power amplifiers from Accuphase have long been blending the purity of class A operation with the superior performance of power MOS-FETs. Acclaimed by audiophiles the world over, these products reflect a level of technical know-how that is second to none. Completing the A series lineup, the A-45 is ideal for systems that demand not quite the high power levels of the A-60 but require more power than the A-30 provides. The A-45 of course also demonstrates the same unwavering dedication to sound quality and outstanding design policy which are the hallmark of Accuphase. This pure class A stereo power amplifier with its distinctive external heat sinks is built for the true enjoyment of music. The so-called instrumentation amplifier principle is used throughout. The signal handling stages feature further improved MCS+ topology and the renowned current feedback approach. This results in electrical characteristics that surpass even the demanding standards set by its predecessors. Employing only highest grade materials and strictly selected parts, the A-45 realizes the two most important goals of an amplifier: very low output impedance and constant drive voltage. The output stage features power MOS-FETs renowned for their excellent sound and superior reliability. For each channel, six of these devices are arranged in a parallel push-pull arrangement. Because MOS-FETs have negative thermal characteristics, there is no danger of thermal “runaway” as exists with bipolar transistors. Operation remains totally stable even when the amplifier is running hot. Driving these devices in pure class A assures high-definition sound that brings out the finest nuances in the music. The heavy-duty power supply features a massive power transformer rated for a maximum of 600 VA, plus two smoothing capacitors of 47,000 μF each. This easily sustains output levels of as much as 360 watts per channel into 1 ohm (with music signals). If even higher power is required, bridged mode turns the A-45 into a high-grade monophonic power amplifier. n Power modules with 6-parallel push-pull arrangement of power MOS-FETs deliver 360 watts per channel into 1 ohm (music signals only), 180 watts into 2 ohms, 90 watts into 4 ohms, or 45 watts into 8 ohms. n Amply dimensioned power supply with high-efficiency toroidal transformer and large filtering capacity. The high-efficiency toroidal transformer is rated for 600 VA, and the two extralarge 47,000 μF aluminum electrolytic capacitors were selected for best sonic performance. Toroidal power transformer n Bridged mode allows upgrading to monophonic amplifier with 720 watts into 2 ohms (music signals only), 360 watts into 4 ohms, or 180 watts into 8 ohms. Bridged connection increases the output by a factor of 4, creating dramatic power reserves in a monophonic configuration. n Four gain control settings minimize residual noise. Filtering capacitors The gain control switches gain in the first stage of the instrumentation amplifier. Four settings are available (MAX, –3 dB, –6 dB, –12 dB). n Fully balanced input stage shuts out external noise interference. n Mode selector for easy switching between dual mono/stereo/bridged operation. n PCB copper foil and all major signal path components are gold-plated. Gain selector n Large analog power meters with off switch and sensitivity selector. n Oversize speaker terminals accept also Y lugs. Meter and input buttons Power MOS-FETs Large speaker terminals Balanced input connectors Parts selected for sound quality and reliability Gold-plated parts Assembly with meter and protection circuitry Instrumentation amplifier Bias stabilizer circuit + INPUT Bias stabilizer circuit Output current (A) Bias stabilizer circuit Bias stabilizer circuit – INPUT Bias stabilizer circuit Gain control MCS+ (Multiple Circuit Summing-up) Fig. 1 Circuit diagram of amplifier section (one channel) Output voltage (V) Power MOS-FETs 6-parallel push-pull 1-ohm operation possible with music signals only Fig. 2 Load impedance vs. output power (output voltage/output current) Instrumentation amplifier and further refined MCS+ topology Instrumentation amp configuration allows fully balanced signal paths The newly adopted “instrumentation amplifier” principle ensures that all signal paths from the inputs to the power amp stage are fully balanced. This results in excellent CMRR (common Signal input stage Power amplifier stage + INPUT – INPUT Instrumentation amplifier configuration n Power amplifier assembly Power amplifier assembly with six parallel push-pull power MOS-FET pairs per channel mounted directly to large heat sink, MCS+ circuitry, and current feedback amplifier. mode rejection ratio) and minimal distortion. Another significant advantage is that external noise and other external influences are virtually shut out. The result is a drastic improvement in operation stability and reliability. Further refined MCS+ topology for even lower noise Accuphase’s original MCS (Multiple Circuit Summing) principle uses a number of identical circuits connected in parallel to achieve superior performance characteristics. MCS+ is a further refined version of this approach. By extending parallel operation to the class-A drive stage of the current/voltage converter, the noise floor has been lowered further. Current feedback principle assures excellent phase characteristics in high range As shown in the illustration, the A-45 uses the output signal current rather than voltage for feedback. Since the impedance at the current feedback point is very low, there is almost no phase shift. A minimal amount of NFB therefore results in maximum improvement of circuit parameters. – Input Buffer + Input Buffer Current adder I-V converter Amplifie Trans-impedance amplifie Current NFB network Principle of current feedback amplifier Output Connection example for bi-amping setup Left loudspeaker In 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. Connection example for bridged setup Right loudspeaker Left loudspeaker Right loudspeaker In bridged mode, the A-45 becomes a monophonic amplifier with even higher power output. For stereo operation, two A-45 units are required. The speakers must have a built-in crossover network and separate inputs for LOW and HIGH range. Two A-45 units are required. A-45 for right channel A-45 for left channel Mode selector of A-45 (DUAL MONO position) A-45 for left channel A-45 for right channel m Use the LEFT (BALANCED or UNBALANCED) input connectors for both A-45 units. m Use the LEFT (BALANCED or UNBALANCED) input connectors for both A-45 units. Mode selector of A-45 (BRIDGE position) Preamplifier n Front Panel Preamplifier GUARANTEED SPECIFICATIONS [Guaranteed specifications are measured according to EIA standard RS-490.] m Continuous Average Output Power (20–20,000 Hz) Stereo operation 360 watts per channel into 1 ohm( ) (both channels driven) 180 watts per channel into 2 ohms 90 watts per channel into 4 ohms 45 watts per channel into 8 ohms Monophonic operation (bridged connection) 720 watts into 2 ohms( ) 360 watts into 4 ohms 180 watts into 8 ohms Note: Load ratings marked ( ) apply only to operation with music signals. m Total Harmonic Distortion Stereo operation (both channels driven) 0.05% with 2 ohm load 0.03% with 4 to 16 ohm load Monophonic operation (bridged connection) 0.03% with 4 to 16 ohm load n Rear Panel m Intermodulation Distortion 0.004% m Frequency Response At rated output: At 1 watt output: m Gain 28.0 dB (with GAIN selector at MAX) (in stereo and monophonic operation) m Gain Selection 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, 0.5 ~ 160,000 Hz +0, –0.2 dB –3.0 dB With music signals only, 1-ohm loads are permissible for stereo operation and 2-ohm loads for monophonic operation. m Damping Factor 200 m Input Sensitivity (with 8-ohm load, GAIN selector in MAX position) Stereo operation: 0.76 V for rated output 0.11 V for 1 watt output Monophonic operation: 1.51 V for rated output 0.11 V for 1 watt output m Input Impedance Balanced: 40 kilohms Unbalanced: 20 kilohms m Signal-to-Noise Ratio (A-weighted, input shorted) 115 dB (GAIN selector in MAX position) 120 dB (GAIN selector in –12 dB position) At rated output Left/right channel output power meters (dB and % scale) Function indicators METER –20 dB, UNBALANCED, BALANCED, BRIDGE Meter operation/illumination button ON OFF Meter sensitivity selector button (–20 dB) Input selector button UNBALANCED BALANCED Power switch Gain selector MAX –3 dB –6 dB –12 dB Unbalanced inputs Balanced inputs Ground Inverted (–) Non-inverted (+) Left/right channel speaker output terminals Mode selector DUAL MONO NORMAL BRIDGE AC power supply connector m Output Level Meters Logarithmic scale, with defeat switch, and sensitivity switch (–20 dB) –50 dB to +3 dB (indication in dB and %) m Power Requirements AC 120 V/230 V, 50/60 Hz (Voltage as indicated on rear panel) m Power Consumption 235 watts idle 430 watts in accordance with IEC 60065 m Maximum Dimensions Width 465 mm (18-5/16") Height 211 mm (8-5/16") Depth 464 mm (18-1/4") m Mass 30.9 kg (68.1 lbs) net 38.0 kg (83.8 lbs) in shipping carton Remarks This product is available in versions for 120/230 V AC. Make sure that the voltage shown on the rear 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 and destination country. n Supplied accessory m m AC power cord Specifications and design subject to change without notice for improvements. http://www.accuphase.com K0605Y PRINTED IN JAPAN 851-0158-00 (AD1)
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