Accuphase E 307 Brochure

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Accuphase E 307 Brochure

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Witness another revolution in sound. Integrated amplifier realizes digital input via option board with high-precision MDS (Multiple Delta Sigma) D/A converter. Current feedback topology assures superb high-range phase fidelity. Wide-band power transistors in parallel push-pull configuration and large power transformer deliver 140 watts/channel into 4 ohms and 100 watts/ channel into 8 ohms. Based on the highly successful Accuphase E-306V which has become a mainstay in the category of integrated amplifiers, the E-307 is a further enhanced and accomplished product for totally faithful music reproduction. It reflects the extensive experience Accuphase has gained in building superb separate-type amplifiers. Every single aspect has been honed to deliver optimum performance. An integrated amplifier provides various advantages such as convenient operation and modest space requirements. However, because its overall gain is very high, even the slightest interference or crosstalk at the input can have a considerable effect on the signal provided at the output. To preclude this possibility, the E-307 is built with totally separate preamplifier and power amplifier sections. Both electrically and structurally, these two parts operate completely autonomously. Each has its own power supply and dedicated regulator circuitry. A dedicated set of inputs and outputs even allows using the preamplifier and power amplifier as if they were stand-alone components. Accuphase's highly acclaimed current feedback topology is used in both the preamplifier and power amplifier. This innovative principle eliminates phase shifts in the upper frequency range and assures stable operation and uniform frequency response which does not change with gain. Phase compensation can be kept at a minimum, and high amounts of negative feedback with their associated disadvantages are no longer required, resulting in excellent transient response, with superb sonic transparency and detail. A total of six input positions are provided, including two balanced inputs for professional-quality noise- free signal transmission. The tape enthusiast will welcome connectors for two tape recorders, with easy dubbing in both directions. Tone controls, loudness compensation, and other convenient features come in handy. Flexibility is fur ther enhanced by the option to install a Digital Input Board with a high-precision MDS (Multiple Delta Sigma) D/A converter that directly accepts the digital signal from a CD player or similar, for un- compromiing reproduction quality. An analog disc input board is also available, allowing high-grade reproduction of analog records.Parallel push-pull output stage delivers quality power: 140 watts/channel into 4 ohms, 100 watts/ channel into 8 ohms Figure 1 shows a circuit diagram of the power amplification stage. The power transistors are multi- emitter types designed for audio applications. They have been selected for optimum frequency response, forward-current transfer ratio linearity, and switching performance characteristics. Arranged to achieve low impedance, the devices are connected in parallel and mounted directly on a large heat sink for efficient dissipation of ther mal energy. This allows the E- 307 to deliver ample power output, amounting to 140 watts into 4 ohms, 120 watts into 6 ohms, or 100 watts into 8 ohms per channel. Current feedback circuit topology in power amplifier and preamplifier sections prevents phase shifts In the E-307, the signal current rather than the more conventionally used voltage is used for feedback. Figure 2 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 converts the current into a voltage to be used as the feedback signal. Since the impedance at the current feedback point (current adder in Figure 2) is very low, there is almost no phase shift. Phasecompensation can be kept to a minimum, resulting in excellent transient response and superb sonic transparency. Figure 3 shows frequency response for different gain settings of the current feedback amplifier. The graphs demonstrate that response remains uniform over a wide range. Discrete-type line amplifier for superior sonic purity To assure optimum performance, the line amplifier is built entirely from discrete parts. A pure complementary push-pull circuit is used, and current feedback topology enhances circuit operation. This reduces the need for phase compensation, resulting in effortless, utterly natural and transparent sound. Highly reliable logic-controlled relays Program source switching is performed by logic- controlled relays which are arranged to permit the shor test possible signal paths. The her metically sealed relays are high-quality types developed specifically for demanding communication applications. The contacts are twin crossbar types plated with gold for minimum contact resistance and outstanding long-term reliability. Tone controls use summing active filters for pure sound The tone control circuitry in the E-307 was specially designed with summing active filters such as found in high-quality graphic equalizers. Figure 4 illustrates the operation principle of this circuit. The flat signal is passed straight through, and only when an adjustment is required, the characteristics are created at F1 and F2 and added to the signal, Figure 1 Circuit diagram of power amplifier section (one channel) Fig. 3 Frequency response with current feedback(response remains uniform also when gain changes) Figure 2 Principle of current feedback amplifier High-current power transiters Relays connected directly to gold-plated input/output jacks