Accuphase A 60 Brochure

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Accuphase A 60 Brochure

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Aiming for the ne plus ultra Experience the peerless sound of pure class A and MOS-FETs. Input stage with MCS topology assures impeccable performance in all aspects with minimum noise and distortion. 10-parallel push- pull power MOS-FETs operating in pure class A, and power supply with massive 1 kVA toroidal transformer deliver linear power into ultra-low impedances down to 1 ohm. 4-step gain selector further reduces residual noise. The monophonic power amplifier M-8000 as well as the stereo power amplifiers P-7000 and P-5000 from Accuphase are highly acclaimed milestones in the history of high-class amplifiers. Featuring similar design technology as these models, the A-60 is a no-holds-barred pure class A stereo amplifier. Accuphase also has created a long and distinguished line of high-output pure class A amplifiers. The musical qualities of our A-100, A-50, and A-50V models have won the admiration of audio connoisseurs the world over. The A-60 is a worthy heir of this tradition. In the input stage, the inventive MCS principle pushes the noise floor down to amazingly low levels. Current feedback topology combines operation stability with excellent frequency response. Only minimal amounts of negative feedback are needed, which is highly beneficial in terms of sound quality. At the same time, the A-60 is designed to realize two major goals: very low output impedance (Note 1), and constant drive voltage (Note 2). The power MOS-FETs used in the output stage are renowned for their superior sound and high reliability. Ten pairs of these devices are arranged in a parallel push-pull configuration for each channel. These superb devices are driven in a pure class A circuit configuration. Reflecting Accuphase's vast expertise and unwavering dedication to sound quality, the A-60 brings out even the most delicate nuances in the source with full authority. Pure class A operation means that the circuit always draws the same amount of power from the power supply, regardless of the presence or absence of a music signal. It is impervious against external influences and has high stability. The output stage produces considerable amounts of thermal energy, but because the MOS-FET devices used in the A-60 have negative thermal characteristics, there is no danger of thermal runaway as exists with bipolar transistors. In addition, extra-large heat sinks on both sides of the amplifier help to prevent internal heat buildup. Another attractive feature of the A-60 is the sophisticated power meters with digital readout and bar graph indication. A dedicated DSP performs arithmetic operations that allow the meters to always show the true power levels of the constantly changing music signal. BIAS STABILIZER BIAS STABILIZER BIAS STABILIZER CONSTANT CURRENT CIRCUIT Output current (A) Output voltage (V) Note 1 Low amplifier output impedanceThe load of a power amplifier, namely the loudspeaker generates a counterelectromotive force that can flow back into the amplifier via the NF 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 made as low as possible by using output devices with high current capability. This absorbs the counterelectromotive force generated by the voice coil and prevents the occurrence of intermodulation distortion. Note 2 The constant drive voltage principleEven in the presence of a load with wildly fluctuating impedance, the ideal power amplifier should deliver a constant voltage signal to the load. Figure 2 shows the results of actual output voltage/ output current measurements at different load impedances for the A-60. It can be clearly seen that output voltage is almost constant at various loads, which means that current increases in a linear fashion. Actual measurements of clipping power have yielded the following figures, which impressively demonstrate the more than ample performance of the A-60: 1 ohm: 513 watts, 2 ohms: 343 watts, 4 ohms: 202 watts, 8 ohms: 110 watts. Fig. 2 Output power vs. load impedance (output voltage/output current) * 1-ohm operation possible with music signals only Power MOS-FET output stage with 10-parallel push- pull power units delivers 480 watts into 1 ohm, 240 watts into 2 ohms, 120 watts into 4 ohms, or 60 watts into 8 ohms with outstanding linearity * 1-ohm loads to be driven with music signals only The output stage (Figure 1) uses power MOS-FETs. 10 pairs of these devices are arranged in a parallel push-pull configuration for each 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 the actual power load per pair is only 6 watts, so that each device is driven only in its low-power rangewhere linearity is excellent. A music signal consists of a continuous succession of pulse waveforms. To prevent clipping on occasional momentary high-level pulses, the maximum clipping level of the A-60 is set to 100 watts per channel into 8 ohms. MCS topology in input stage reduces residual noise and drastically improves S/N ratio The input stage which has an important role to play features Accuphase's innovative MCS (Multiple Circuit Summing) design. Three separate unit amplifiers for the input signal are connected in parallel, which minimizes noise and distortion and greatly improves other performance parameters as well. This manifests itself in further improved sound quality. Gain control also switches NFB for reduced noise floor The gain control of the A-60 has four positions: MAX, -3 dB, -6 dB, -12 dB. Reducing the gain also results Fig. 1 Circuit diagram of amplifier section (one channel) Power MOS-FETs

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in correspondingly lower noise, which can be very beneficial when driving high-efficiency speakers where residual noise can be a problem. Current feedback circuit topology assures excellent phase characteristics in high range In the A-60, the signal current rather than the more conventionally used voltage is used for feed- BufferCurrent adder I-V converter Trans-impedance amplifier Amplifier Output Current NFB network - Input Buffer + Input back. Since the impedance at the current feed- back point (current adder in Figure 3) is very low, there is almost no phase shift. Phase compensa- tion therefore can be kept at a minimum. A minimal amount of NFB results in maximum improvement of circuit parameters. The result is excellent tran- sient response and superb sonic transpar- ency, coupled with utterly natural energy balance. Figure 4 shows fre- quency re- sponse for dif- Gain (Large) (High) Frequency ferent gain settings of the cur- rent feedback amplifier. The graphs dem- onstrate that response remains uniform over a wide range. Bridged operation mode creates true monophonic amplifier with 960 watts into 2 ohms, 480 watts into 4 ohms or 240 watts into 8 ohms * 2-ohm loads to be driven with music signals only Bridged connection turns the A-60 into a monophonic amplifier with four times more power than during stereo operation. The result is an extremely capable performer with almost unlimited reserves. Robust power supply with large "Super Ring" toroidal transformer and 82,000 µF filtering capacity The power supply section is a critical aspect of any power amplifier. The A-60 features a large toroidal power transformer with a rating of about 1 kVA. The transformer is housed in a non-resonantaluminum enclo- sure filled with damping material that has excellent heat transfer char- acteristics. Toroi- dal transformers which use heavy- gauge copper wir- ing on a ring- shaped core have important advan- tages for audio ap- plications, such as very low imped- ance, small size, and high conver- sion efficiency. Power amplifier assembly with 10- parallel push-pull output devices mounted to large heat sink, MCS circuit, and current feedback amplifier circuitry (one channel) Fig. 4 Frequency response with current feedback(Response remains uniform also when gain changes) Fig. 3 Principle of current feedback amplifier