Accuphase A 65 Brochure
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547W 365W 214W 118W 61W 5 0 10 15 20 25 0 5 10 15 20 25 30 35 + B3 - B3 - + +- + B1 - B1 - B2 + B2 Q1 Q3 Q2 Q4 Q8 Q6 Q7 Q5 Q9 Q17 Q21 Q19 Q18 Q20 Q22 Q23 Q24 Q25 Q27 Q29 Q31 Q26 Q28 Q30 Q32 Q33 Q34 Q35 Q36 Q37 Q38 Q39 Q40 Q41 Q42 Q13 Q11 Q15 Q10 Q14 Q12 Q16 -+ Power MOS-FETs n Power modules with 10-parallel push-pull arrangement of power MOS-FETs deliver 480 watts per channel into 1 ohm (music signals), 240 watts into 2 ohms, 120 watts into 4 ohms, or 60 watts into 8 ohms. n Strong power supply with high-effi ciency toroidal transformer and two extra-large 82,000 μF fi ltering capacitors. n Bridged mode supports upgrading to monophonic amplifi er with 960 watts into 2 ohms (music signals), 480 watts into 4 ohms, or 240 watts into 8 ohms. n Instrumentation amplifi er principle allows fully balanced signal paths, and current feedback amplifi er topology drastically improves S/N ratio. n Four gain control settings (MAX, –3 dB, –6 dB, –12 dB) minimize residual noise. n Fully balanced input stage shuts out external noise interference. n Dual mode power meters, switchable to 5-digit numeric readout or 25-point LED bar graph indication. ● Meter circuit ON/OFF switch. ● Digital power meters show true output power values, based on output current detected by a Hall element. ● Peak value hold time settings: 1 second, . n Input selector button (balanced/unbalanced) on front panel. n Mode selector with dual mono position supports bi- amping. n Oversize speaker terminals accept also Y lugs. The combination of pure class A and power MOS-FET devices to realize high output power with excellent sonic purity is a domain where Accuphase excels. Models such as the A-100, A-50V, and A-60 have achieved legendary status among audiophiles and represent an unrivaled level of technological excellence. As a model-change successor to the A-60, the new A-65 incorporates accumulated Ac- cuphase know-how while featuring a number of further im- provements. The input stage is confi gured as an instrumen- tation amplifi er to allow fully balanced input signal paths. The further refi ned MCS+ topology pushes noise and dis- tortion down to absolutely minimal levels, and strictly se- lected materials and parts of the highest quality are used throughout. The end result is a high-end class A stereo am- plifi er with simply stunning performance and sound quality. The output stage of the A-65 features power MOS-FETs renowned for their excellent sound and superior reliability. For each channel, ten of these devices are arranged in a parallel push-pull arrangement. MOS-FETs have excellent frequency characteristics, and their high input impedance reduces the load imposed on the preceding drive stage. They also have negative thermal characteristics, which ensures perfect operation stability. Driving these devices in pure class A produces rich, high-defi nition sound that brings out the fi nest nuances in the music. In a pure class A amplifi er, the power provided by the power supply is always constant, regardless of the presence of a musical signal. This means that the amplifi er remains unaffected by fl uc- tuations in voltage and other external infl uences. On the other hand, it also means that the output stage generates considerable thermal energy. In the A-65, this is dissipated effectively by large heat sinks which provide ample capacity to remove the heat pro- duced by the internal circuitry. The high-effi ciency toroidal power transformer housed in an alumi- num diecast enclosure, in conjunction with amply dimensioned smoothing capacitors, provides the muscle to deliver an astonishing 480 watts per channel into a 1-ohm load (music signals only). If even higher power reserves are required, bridged mode turns the A-65 into a superlative mono- phonic power amplifi er. Pure Class A power amplifi er with power MOS-FET devices - Input stage features ful- ly balanced signal paths as found in high-quality instrumentation amplifi ers. Further refi ned MCS+ topology and current feedback result in superb sound quality and out- standing performance parameters. Strong power supply section and power MOS-FET devices in ten-parallel push-pull confi guration sustain linear power output progression down to impedances as low as 1 ohm. Digital power meters show true power readings. INPUT Large speaker terminals Figure 1 Circuit diagram of amplifi er section (one channel) Hall element Toroidal power transformer Bias stabilizer circuit NFB NETWORK Mode selector Gain selector Meter circuitry/control circuitry assemblyFiltering capacitors Unbalanced and balanced input connectors NFB NETWORK GAIN CONTROLBias stabilizer circuit Bias stabilizer circuit Bias stabilizer circuitNFB NETWORK REGULATOR REGULATOR INPUT MCS+ (MultipleCircuit Summing) Gain control Instrumentation amplifi er 10-parallel push-pull power MOS-FET array Output voltage (V) Output current (A) Figure 2 Load impedance vs. outpu t (output voltage/output cur r > 1-ohm operation p with music signal s OUTPUT Bias stabilizer circuit
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40 45 +- - + +- +- - + n Power amplifi er assembly Power amplifier assembly with 10-parallel push-pull power MOS- FET pairs per channel mounted directly to large heat sink, MCS+ circuitry, and current feedback amplifi er. Instrumentation amplifi er and further refi ned MCS+ topology Instrumentation amp confi guration allows fully balanced signal paths The newly adopted instrumentation amplifi er principle ensures that all signal paths from the inputs to the power amp stage are fully balanced. This results in excellent CMRR (Common Mode Rejection Ratio) and minimal distortion. Another signifi cant advantage is the fact that external noise and other external infl uences are virtually shut out. The result is a drastic improvement in operation stability and reliability. Further refined MCS+ topology for even lower noise Accuphases original MCS (Multiple Circuit Summing) principle uses a number of identical circuits connected in parallel to achieve superior performance characteristics. MCS+ is a further refi ned version of this approach. By extending parallel operation to the class-A drive stage of the current/voltage converter, the noise fl oor has been lowered further. t power ent) ossible s only Current feedback principle assures excellent phase characteristics in high range As shown in the illustration, the A-65 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 NFB NETWORK GAIN CONTROL CIRCUIT INPUT NFB NETWORK Signal input stage Power amplifi er stage OUTPUT Instrumentation amplifi er confi guration INPUT OUTPUT INPUT Current NFB network I/V converter Current adder Trans-impedance amplifi er Amp- lifi er Principle of current feedback amplifi er Buffer Buffer