Accuphase E 408 Brochure

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Accuphase E 408 Brochure

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High-output, high-performance integrated amplifier with MCS topology in preamplifier and power amplifier stages. Current feedback ensures optimum phase characteristics in high frequency range. Wide-band power transistors in triple push-pull configuration and high-efficiency R-toroidal power transformer deliver plenty of quality power: 260 watts per channel into 4 ohms or 180 watts into 8 ohms. Option boards can be used to implement digital input or analog record playback with impeccable quality. Q11 Q13 Q15 Q12 Q14 Q16 Q10 Q8 Q6 Q5 Q7 Q9 +- OUTPUT INPUT - B1 +B1 - B2 +B2 REGULA- TOR REGULA- TOR NFB NETWORK Q1a Q3a Q2a Q4a Q1b Q3b Q2b Q4b BIAS STABILIZER CIRCUIT Triple parallel push-pull power unit delivers 260 watts/ch into 4 ohms, 220 watts/ch into 6 ohms, and 180 watts/ch into 8 ohms The power transistors used in the output stage are multi-emitter devices designed for audio applications, with optimum frequency response, forward-current transfer ratio linearity, and switching performance characteristics. By arranging these devices in a triple parallel configuration (Figure 1), low impedance is The E-408 is a further refined and enhanced version of the highly popular and successful E-407. Incorporating latest technology and using only top quality parts, the E-408 is an integrated amplifier that stands out through sheer excellence. S/N ratio in the preamplifier and power amplifier sections has been further improved by the adoption of MCS (Multiple Circuit Summing). Musical dynamics never sounded so impressive, with every nuance clearly outlined. The E-408 is the yardstick by which integrated amplifiers will be measured from now on. Because an integrated amplifier has very high overall gain, 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-408 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 separate set of inputs and outputs even allows using the preamplifier and power amplifier as if they were stand-alone components. The circuits in the preamplifier and power amplifier stages both use the MCS principle as well as current feedback. MCS is a sophisticated technique developed by Accuphase for connecting multiple circuits in parallel. The overall result of combining these circuit topologies are improved performance specs as well as superior sound quality. The output stage of the power amplifier is constructed as a triple parallel push-pull configuration of multi-emitter type power transistors designed for high-current audio applications. The efficient R-toroidal power transformer in the power supply and plenty of filtering capacity support 260 watts per channel (4 ohms) or 180 watts (8 ohms). The preamplifier section features tone controls and a loudness compensator designed to retain the purity of the music signal. Functions such as recordermonitoring and copying provide welcome flexibility. All major parts were selected by strict listening evaluation to assure a high all-round standard of quality. A Digital Input Board using a high-precision MDS (Multiple Delta Sigma) D/A converter is available as an option, allowing the digital signal of a CD player or similar to be directly supplied to the E-408. Another option is an Analog Disc Input Board for high-grade reproduction of analog records. achieved. The transistors are mounted to a large heat sink for efficient dissipiation of thermal energy. As a result, the E-408 provides plenty of high-quality output power. Parallel connection MCS topology in preamplifier and power amplifier stages Both the power amplifier (Figure 1) and preamplifier (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 OUTPUT Q8 Q5 Q7 Q6 +B -B Q4a Q3a Q2a Q1a Q4b INPUT Q3b Q2b Q1b distortion. In the E-408, two separate amplification circuits are fed the same signal, as well as the feedback signal, and the output of the circuits is combined, which is equivalent to parallel operation of the overall circuit. Mathematically, when two parallel circuits are employed, the improvement in S/N ratio is 3 dB. Current feedback circuit topology in power amplifier and preamplifier sections prevents phase shifts In the E-408, the signal current rather than the 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. Figure 4 shows frequency response for different gain settings of the current feedback amplifier. The graphs demonstrate that response remains uniform over a wide range. Fig. 2 Line amplifier circuit diagram Fig. 1 Power amplifier circuit diagram (one channel) BufferCurrent adder I-V converter Trans-impedance amplifier Amplifier Output Current NFB network Input Fig. 3 Current feedback amplifier principle diagram Fig. 4 Frequency response with current feedback (response remains uniform even when gain changes)

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Logic-controlled relays for signal switching assure high sound quality and long-term reliability All signal switching is performed by logic-controlled relays which are arranged so as to permit the shortest High-efficiency toroidal power transformer and high filtering capacity The power supply section is a critical aspect of any power amplifier. The E-408 features a large to- roidal power trans- former with a rating of 600 VA. The trans- former is housed in a non-resonant alu- minum enclosure filled with damping material that has excellent heat transfer character- istics. Two large 33,000 µF capaci- tors smooth out any current irregulari- ties. This no-holds- barred approach manifests itself in rock-solid, powerful sound even at ultra-deep fre- quencies. Tone controls with summing active filters for best sound The tone control circuitry in the E-408 was specially designed with sum- ming active filters such as found in high-quality graphic equalizers. Figure 5 il- lustrates the operation principle of F1 -A1 -A2 VR1 F2 VR2 Input Output Fig. 5 Tone control principle (Summing active filter type) Two sets of large size speaker terminals The speaker terminals are made of extruded high- purity brass material which accept also heavy-gauge speaker cable. Two sets of outputs with a speaker selector are provided, and bi-wiring (supplying the same signal via dual leads to speakers with separate high-frequency and low-frequency inputs) is also possible. this circuit. The flat signal is passed straight through, and only when an adjustment is required, the charac- teristics are created at F 1 and F 2 and added to the signal, thereby producing the desired change. This design provides efficient control without diluting sig- nal purity.possible signal paths. 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. Output stage with triple parallel push-pull arrangement, MCS, and current feedback circuitry mounted to large heat sink Supplied remote commander RC-20 allows volume adjustment and input source switching