Accuphase M 8000 Brochure
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Extracted text from Accuphase M 8000 Brochure (Ocr-read)
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A monophonic power amplifier with impressive muscle: 2000 watts into 1 ohm MCS topology for input stage assures high S/N ratio. 22 wide-band high power transistors in parallel push-pull configuration. Power supply with massive 3 kVA toroidal power transformer realizes constant voltage speaker drive and delivers linear power down to impedances as low as one ohm. Teflon PCBs with low dielectric constant and minimum loss. When developing the M-8000, Accuphase took a fresh look at the entire concept of the power amplifier. As a result, the M-8000 was designed to realize the ideal of constant voltage drive, which is best implemented in a monophonic configuration. In order to bring out the full performance potential of any loudspeaker, unaffected by the often drastic fluctuations in speaker impedance, the amplifier must have very low output impedance (Note 1), and it must be able to supply a constant drive voltage (Note 2). In the M-8000, a complement of 22 output transistors with a collector dissipation (Pc) of 150 watts each is used in the output stage. Connected in parallel, these devices have a combined collector dissipation of 6,600 watts. At the extremely low load impedance of 1 ohm, the amplifier is rated to deliver an amazing 2,000 watts. Constant voltage drive enables linear progression of output vs. load impedance. This performance is sustained by a massive Super Ring toroidal transfor mer housed in a diecast enclosure with directly mounted heat sinks, and by large filtering capacitors. The transformer is rated for 1,5 kVA, max. 3,0 kVA, and there are two capacitors of 40,000 µF each. This assures more than ample reser ves and allows the M-8000 to meet even the most demanding and rapidly fluctuating power requirements. Use of two units in bridged configuration is also possible, resulting in a mono amplifier with even higher capabilities. The impor tant input stage also has been given due attention. Another Accuphase innovation called MCS (Multiple Circuit Summing) helps to minimize noise. The predriver stage features a DC stabilized power supply. This results in drastically improved S/N ratio, minimum distor tion, and superb performance in all other aspects. Stable output is achieved regardless of fluctuations on the AC side. Current feedback topology makes it possible to combine stable operation with impeccable frequency response. The circuit boards of the M-8000 possess a Teflon base with low dielectric constant and minimum loss. Balanced inputs help to shut out external noise. The copper foil side of PCBs and all input and output terminals as well as all major signal carrying points are gold plated. The overall result of these measures is musical purity that leaves nothing to be desired. * Teflon is a registered trademark of DuPont USA. Ultra-powerful output stage with 22 parallel push- pull transistors delivers 2,000 watts into 1 ohm, 1,000 watts into 2 ohms, 500 watts into 4 ohms and 250 watts into 8 ohms The M-8000 uses a complement of 22 high-power transistors with a collector dissipation (Pc) of 150 watts and a collector current of 15 amperes each. These devices are excellent in every regard, including frequency response, current amplification linearity, and switching characteristics. The 22 devices are connected in a parallel push-pull configuration and mounted to immense heat sinksmade of diecast aluminum. This assures efficient dissipation of thermal energy and provides plenty of performance margin. As a result, the power amplifier is capable of delivering enormous output power in a linear progression towards lower load impedances: 2,000 watts into 1 ohm, 1,000 watts into 2 ohms, 500 watts into 4 ohms and 250 watts into 8 ohms. The M-8000 also is able to drive reactive loads with ease. Figure 2 is a graph plotting the output voltage versus current characteristics. Even when the load changes, the output voltage remains almost constant, showing linear current progression. Actual measurement of clipping power at the extremely low load impedance of 1 ohm yields 2,330 watts. At 2 ohms, the figure is 1,230 watts, at 4 ohms 630 watts, and at 8 ohms 310 watts. This demonstrates the impressive performance reserves of this amplifier. MCS topology in input stage drastically improves S/N ratio The input stage features Accuphase's original 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. Stabilized power supply in driver stage assures outstanding operation stability The MCS circuitry and predriver stage employ a DC stabilized power supply. When the power stage amplifies a signal to large amplitudes, this could cause noise in the input stage via the power supply. This is prevented by fixing the voltage of the predriver stage, to improve the quality of the power supply for the low-level amplification stages. Outstanding S/N ratio and stable operation unaffected by ambient temperature and by AC line fluctuations is guaranteed at all times. Note 1: Low amplifier output impedance When forming the load of a power amplifier a 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 output circuitry. The internal impedance of a power amplifier should therefore be made as low as possible by using output devices with high current capability. Note 2: Constant drive voltage principle Even when the impedance of a load fluctuates drastically, the ideal power amplifier should deliver a constant voltage signal to the load. When the supplied voltage remains constant for any impedance, output power will be inversely propor tional to the impedance of the load. A conventional amplifier can be easily made to operate in this way down to a load impedance of about 4 ohms. However, at 2 ohms and below, much more substantial output reser ves are needed. This can only be achieved by a thorough redesign of all basic amplifier aspects. Bias stabilizer circuit Bias stabilizer circuit Constant current circuit Bias stabilizer circuitBias stabilizer circuit Fig. 1 Circuit diagram of amplifier section Fig. 2 Output power vs. load impedance(output voltage/output current: actual measurements) * 1-ohm oper ation possible with music signals only Output voltage (V) Output current (A)
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Power amplifier assembly with MCS circuit, current feedback amplifier circuitr y, and output stage with 22 parallel push-pull transistors mounted directly to two large aluminum diecast heat sinks Current feedback circuit topology prevents phase shifts in high frequency range The M-8000 employs the original Accuphase current feedback pr inciple. Figure 3 shows the operating principle of this circuit. At the sensing point of the feedback loop, the impedance is kept low and current detection is performed. An impedance- converting amplifier then tur ns the current into a voltage to be used as the feedback signal. Since the impedance at the current feedback point (current adder in Figure 3) is ver y low, there is almost no phase shift. Phase compensation can be kept to a minimum, resulting in excellent transient response and superb sonic transparency. Figure 4 shows frequency response fordifferent gain settings of the current feedback amplifier. The graphs demonstrate that response remains unifor m over a wide range. Use of two M-8000 in bridged configuration possible, resulting in a mono amplifier with four times the power Bridged operation means that two amplifiers are driven by the same signal voltage but with opposite phase. The speaker load is then connected between the positive output terminals of the amplifiers. When used in a bridged configuration, two M-8000 units for m a single mono amplifier with awesome power capabilities: 4,000 watts into 2 ohms, 2,000 watts into 4 ohms, or 1,000 watts into 8 ohms.Printed circuit boards made from Teflon with low dielectric constant and low loss The printed circuit boards for the signal-carrying circuits are made of Teflon, a glass fluorocarbon resin material. Teflon has extremely low specific inductive capacity which is desirable for fast signal transmission and a low dielectric dissipation factor which results in minimal transmission losses. High-frequency characteristics and heat resistance are also excellent. For further improved sound quality, the copper foil side is gold plated. Fig. 3 Current feedback amplifier principle diagram Fig. 4 Frequency response with current feedback (Response remains unifor m even when gain changes) – Input BufferCurrent adder I-V converter Trans-impedance amplifier Amplifier Output Current NFB network + Input Buffer