Accuphase E 407 Brochure
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State-of-the-art integrated amplifier features current feedback topology for superb high-range phase fidelity. Wide-range power transistors in triple parallel push-pull configuration and massive toroidal transformer deliver ample power: 260 watts × 2 into 4 ohms, 180 watts × 2 into 8 ohms. Option board enables analog record reproduction in top-notch quality. The E-407 represents a new pinnacle of ampli- fier design. Featuring latest technology and us- ing only the highest quality materials, this inte- grated stereo amplifier is destined to become a new reference. Frequency response, S/N ratio, and all other performance aspects make the E-407 perfectly suited for the new generation of ultra high quality program sources such as SACD and DVD-Audio. An integrated amplifier provides various advan- tages such as convenient operation and modest space requirements. However, because its over- all gain is very high, even the slightest interfer- ence or crosstalk at the input can have a consid- erable effect on the sonic result. To preclude this possibility, the E-407 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 sepa- rate components. A switch even allows using the preamplifier and power amplifier independently. Accuphase's highly acclaimed current feedback topology virtually eliminates phase shifts in the upper frequency range and assures outstanding performance and sound quality. The power am- plifier output stage employs a triple parallel push- pull configuration, using multi-emitter power tran- sistors designed for high-power audio applica- tions. Ample muscle is provided by the power supply section which features a massive, highly efficient toroidal power transformer housed in a diecast enclosure equipped with heat fins. In the standard configuration, the E-407 has six inputs, two of which employ the balanced princi- ple that assures ideal signal transmission char- acteristics. Provisions for two tape recorders, with easy dubbing in both directions, tone controls, and loudness compensation are further attractive fea- tures. An optional analog disc input board allows reproduction of analog records with outstanding sonic quality. The external design of the E-407 continues the Accuphase tradition, featuring a champagne gold brushed front panel. Two large power meters in the center are flanked by the input selector sec- tion and the volume control. Not only by virtue ofits excellent sound, from its looks as well the E-407 is a great addition to any living room. Triple parallel push-pull output stage delivers quality power: 260 watts/channel into 4 ohms, 220 watts/channel into 6 ohms or 180 watts/ channel into 8 ohms The output devices are multi-emitter power tran- sistors designed for high-power audio applica- tions. These devices have excellent frequency re- sponse, forward-current transfer ratio linearity, and switching performance characteristics. They are connected in a triple parallel configuration (Fig- ure 1) for low impedance and mounted directly on a large heat sink to assure ef- ficient dissipation of thermal energy. This allows the E- 407 to deliver am- ple power output, amounting to 260 watts into 4 ohms, 220 watts into 6 ohms, or 180 watts into 8 ohms per channel. Current feedback topology in power amplifier and preamplifier sections guarantees top- level performance In the E-407, the signal current rather than the 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 im- pedance-converting amplifier then converts the current into a voltage to be used as the feedback signal. Since the impedance at the current feed-back point (current adder in Figure 2) is very low, there is almost no phase shift. Phase compensa- tion can be kept to a minimum, resulting in excel- lent transient response and superb sonic transparency. Figure 3 shows frequency re- sponse for dif- ferent gain set- tings of the cur- rent feedback amplifier. The graphs demonstrate that response remains uniform over a wide range. Discrete-type line amplifier for superior sonic purity The line amplifier is entirely built from discrete par ts, to assure optimum performance. Using a principle developed by Accuphase, a differential pure complementary push-pull circuit is combined with a single-ended push-pull emitter follower output stage. This comparatively simple topology reduces the need for phase compensation, re- sulting in effortless, utterly natural and transpar- ent sound. Highly reliable logic-controlled relays Program source switching is performed by logic- controlled relays which are arranged so as to permit the shortest possi- ble signal paths. The her metically sealed relays are high-qual- ity types devel- oped specifi- cally for de- manding com- munication ap- plications. 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 circuitr y in the E-407 was spe- cially designed with summing active filters. Fig- ure 4 illustrates the operation principle of this cir- High-current power transistors Relays connected directly to gold-plated input/output jacks Figure 2 Principle of current feedback amplifier Figure 1 Circuit diagram of power amplifier section (one channel) Figure 3 Frequency response with current feedback (Response remains unifor m also when gain changes) Line amplifier assembly with current feedback circuitry Bias stabilizer
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cuit. The flat signal is passed straight through, and only when an adjustment is required, the characteris- tics created at F1 and F2 are added to the signal, thereby pro- ducing the desired change. This design pro- vides efficient control with- out degrading signal purity. Large toroidal power transformer and high fil- tering capacity The power supply section is a critical aspect of any power amplifier. The E-407 features a large toroidal power transformer with a rating of 600 VA. The transformer is housed in a non-resonant aluminum enclosure filled with damping material that has excellent heat transfer characteristics. Toroidal transformers which use heavy-gauge copper wiring on a ring-shaped core have vari- ous advantages, such as very low impedance, small size, and high conversion efficiency. The toroidal type transformer used by Accuphase is ideally suited for audio applications. It has the fol- lowing characteristics: aNear-circular core caliber allows near-circular coil windings with high packing density, result- ing in low leakage flux and minimum vibrations. bSmaller ferrite core diameter and copper windings with high specific gravity mean lowferrite losses and low inrush current. Two massive electrolytic capacitors, each rated for 33,000 uF assure ample reserves also for re- production of the most demanding passages. Dedicated headphone amplifier for best sound The E-407 provides a separate amplifier for the phone jack de- signed to provide superior sonic performance. The speaker out- put can be cut off by a switch, and the main volume control can be used to adjust the headphone listening level. Two sets of heavy-duty speaker terminals The oversize speaker terminals are made of extruded high-purity brass material whichaccept also heavy-gauge speaker cable. Two sets of outputs with a speaker selector are provided, and bi-wiring (supply- ing the same sig- nal via dual leads to speakers with separate high-fre- quency and low- frequency inputs) is also possible. Large analog peak power meters The power meters use logarithmic compression to cover a wide dynamic range, letting you easily monitor the output level of the rapidly fluctuating music signal. Meter illumination can be switched off, which is conven- ient for example in a home theater setup. nSupplied remote commander RC-20 Allows volume control and source switching Power amplifier assembly with tri- ple parallel push- pull output devices mounted to large heat sink and cur- rent feedback am- plifier circuitry Heavy-duty speaker terminals Figure 4 Tone control circuit principle (Summing active filter type) Massive filtering capacitors and large toroidal power transformer