Accuphase E 308 Brochure
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Sophisticated MCS topology assures outstanding S/N ratio Enjoy crystal clear sound emerging from a background of utter silence. Current feedback amplification, wide-band power transistors in parallel push-pull configuration, and potent power supply deliver plenty of quality power: 140 watts per channel into 4 ohms or 100 watts into 8 ohms. Option boards allows digital signal input or analog record playback with impeccable quality. Parallel connection MCS topology in preamplifier and power amplifier stages Both the preamplifier (Figure 1) and power amplifier (Figure 2) employ the MCS (Multiple Circuit Summing) topology developed by Accuphase. This design results in significantly improved performance characteristics such as higher S/N ratio and lower distortion. In the E-308, the same signal is supplied to two separate amplification circuits, which also receive the feedback signal. The output of the circuits is combined, which is equivalent to parallel operation of the overall circuit. Mathematically, when using two parallel circuits, the improvement in S/N ratio is 3 dB. The circuit BIAS STABILIZER components of the line amplifier input stage and output stage are also driven in parallel, which further minimizes noise that could arise in the various amplification stages. Current feedback circuit topology in power amplifier and preamplifier sections prevents phase shifts and assures excellent sound quality In the E-308, the signal current rather than the The E-300 series has always played a central role in the Accuphase integrated amplifier lineup. Drawing from a wealth of know-how and experience, the E-308 incorporates the latest advances in circuit technology and materials research. It has been designed to deliver onehundred percent of musical enjoyment. Specially noteworthy is the MCS (Multiple Circuit Summing) topology implemented in the preamplifier and power amplifier sections. It drastically improves S/N ratio, allowing utterly natural sound to emerge from a background of deep silence. An integrated amplifier offers 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 sonic result. To preclude this possibility, the E-308 is designed to achieve total electrical and structural separation of the preamplifier and power amplifier sections. These two parts operate as if they were entirely separate components. An EXT PRE switch and dedicated inputs and outputs allow independent use of the preamplifier and power amplifier. Both the preamplifier and power amplifier use the MCS principle developed by Accuphase, with multiple input circuits connected in parallel. Together with the current feedback topology, this results in a significant enhancement of all vital performance parameters. The power amplifier output stage adopts a parallel push- pull configuration of multi-emitter power transistors designed for high-power audio applications. The large power transformer in the power supply and plenty of filtering capacity sustain ample high- quality output power. The preamplifier section comprises features such as tone controls, loudness compensator, and facilities for recorder monitoring and copying. Each circuit component has been carefully selected after extensive tests. The end result is an integrated amplifier that clearly stands out from the rest. Option boards can be used to implement digital inputs and high-quality analog record playback. more conventionally used voltage is used for feedback. Because there is almost no phase shift, phase compensation can be kept to a minimum, resulting in excellent transient response and superb sonic transparency. Also, frequency response remains uniform over a wide gain range. This is evident from Figure 4 which shows frequency response for different gain settings of the current feedback amplifier. Parallel push-pull output stage delivers quality power: 140 watts/channel into 4 ohms, 120 watts/channel into 6 ohms or 100 watts/ channel into 8 ohms The output devices are multi-emitter power transistors designed for high power audio applications. These devices have excellent frequency response, forward-current transfer ratio linearity, and switching performance characteristics. They are connected in a triple parallel configuration (Figure 2) for low impedance and mounted directly on a large heat sink to assure efficient dissipation of thermal energy. A generous design margin allows the E-308 to deliver ample power output. BufferCurrent adder I-V converter Trans-impedance amplifier Amplifier Output Current NFB network Input Gain (High) Frequency (Large) Fig. 1 Circuit diagram of line amplifier (one channel)Fig. 2 Circuit diagram of power amplifier (one channel) Fig. 3 Principle of current feedback amplifier Fig. 4 Frequency response with current feedback(Response remains uniform also when gain changes) High-power transistors
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Highly reliable logic-controlled relays for best sound quality Program source switching is performed by logic- controlled relays which are arranged so as to permit straight and short signal paths for enhanced sonic purity. The hermetically 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. Two sets of heavy-duty speaker terminals Two sets of oversize speaker terminals are provided which accept also heavy-gauge speaker cable.Large power transformer and high filtering capacity The power supply section is a critical aspect of any power amplifier. The E-308 features a large power trans- former with a rating of 500 VA. The trans- former is mounted in an enclosure filled with damping material that has excellent heat transfer charac- teristics. This design prevents unwanted interaction with the rest of the amplifier. Two massive electro- lytic capacitors, each rated for 22,000 µF, are used to filter the current. This ampleperformance margin of the power supply en- sures dynamic sound down to very deep fre- quencies. Tone controls use summing active filters for pure sound The tone control circuitry in the E-308 features summing active filters. Figure 5 illustrates the operation principle of this circuit. The flat sig- nal is passed straight through, and only when an ad- justment is required, the characteristics created at F 1 and F 2 are added to the signal, thereby producing the desired change. This design provides effi- cient control without degrading signal purity. Input Output Fig. 5 Tone control circuit principle (Summing active filter type) Power amplifier assembly with parallel push-pull output devices mounted to large heat sink, MCS circuit, and current feedback amplifier circuitry. n nn n nSupplied remote commander RC-20 Allows volume adjustment and input source switching Gold-plated input/output jacks with directly connected relays