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Highlights of the E-407's advanced technologies and power capabilities.
Description of the controls and indicators on the front panel.
Details on the output stage design for high-power audio delivery.
Explanation of the current feedback principle for sonic performance.
Describes the discrete-component line amplifier for sonic purity.
Relays ensure short signal paths and reliable switching.
Details the high-capacity power supply for ample reserves.
Explains the summing active filter tone control and loudness compensation.
Describes the logarithmic compression meters for dynamic range monitoring.
Dedicated amplifier for the headphone jack providing superior sonic performance.
Details the input selector and balanced connectors for versatile use.
Describes available optional input boards for expanded functionality.
Lists the technical specifications measured according to EIA standards.
Diagrams and labels for front and rear panel components.
The Accuphase E-407 is an integrated stereo amplifier designed to deliver high-quality audio performance, combining advanced technology with user-friendly features. It is built to serve as a central component in a high-fidelity audio system, capable of handling a wide range of program sources and delivering ample power to speakers.
At its core, the E-407 functions as a stereo amplifier, integrating both preamplifier and power amplifier sections into a single chassis. This design aims to simplify the audio chain while maintaining the performance typically associated with separate components. The amplifier utilizes a current feedback topology, a design choice that Accuphase claims ensures superb high-range phase fidelity and overall operational stability. This approach is intended to minimize phase shifts, particularly in the upper frequency range, contributing to excellent transient response and sonic transparency.
The power amplifier section features a triple parallel push-pull output stage. This configuration employs multi-emitter power transistors specifically designed for high-power audio applications. These transistors are chosen for their excellent frequency response, linearity of forward-current transfer ratio, and switching performance characteristics. They are mounted directly on a large heat sink to ensure efficient dissipation of thermal energy, allowing the amplifier to deliver substantial power output.
The power supply section is robust, featuring a large toroidal power transformer with a rating of 600 VA. This transformer is housed in a non-resonant aluminum enclosure filled with damping material to optimize heat transfer. Toroidal transformers are favored for their low impedance, compact size, and high conversion efficiency, making them well-suited for audio applications due to their low leakage flux and minimal vibrations. Massive electrolytic capacitors, each rated for 33,000 uF, provide ample power reserves for demanding musical passages.
The preamplifier section includes a discrete-type line amplifier, built entirely from discrete parts to ensure optimal performance. It employs a differential pure complementary push-pull circuit combined with a single-ended push-pull emitter follower output stage. This topology is designed to reduce the need for phase compensation, resulting in a natural and transparent sound.
For tone control, the E-407 incorporates summing active filters. This design allows the flat signal to pass straight through, and adjustments are applied only when required, ensuring that signal purity is maintained without degradation.
The E-407 offers a versatile input configuration to accommodate various audio sources. It includes eight input positions, two of which are dedicated to optional input boards, plus two tape recorder connections. Two of the standard inputs (CD and LINE) are designed for balanced connections, which are less susceptible to externally induced noise, ensuring clean signal transmission.
Program source switching is managed by logic-controlled relays. These relays are arranged to provide the shortest possible signal paths, minimizing interference and signal degradation. The hermetically sealed, gold-plated twin crossbar contacts of these relays are chosen for their low contact resistance and long-term reliability.
A high-quality volume control allows for precise adjustment of listening levels. The amplifier also comes with a supplied remote commander (RC-20), enabling convenient control of volume and source switching from a distance.
A "separator" switch allows for independent use of the preamplifier and power amplifier sections, offering flexibility for users who might want to integrate external preamplifiers or power amplifiers into their system.
For personal listening, the E-407 includes a dedicated headphone amplifier. This separate amplifier circuit is designed to provide superior sonic performance through headphones. The speaker output can be cut off via a switch, and the main volume control adjusts the headphone listening level.
The amplifier features two sets of heavy-duty speaker terminals made of extruded high-purity brass. These terminals can accept heavy-gauge speaker cables and support bi-wiring configurations, allowing the same signal to be supplied via dual leads to speakers with separate high-frequency and low-frequency inputs.
Large analog peak power meters are centrally located on the front panel. These meters use logarithmic compression to cover a wide dynamic range, allowing users to easily monitor the output level of the rapidly fluctuating music signal. The meter illumination can be switched off, which can be convenient in specific setups, such as home theater environments.
Optional input boards enhance the E-407's versatility. Two types of boards are available: the Line Inputs Board LINE-10, which provides additional conventional line inputs for connecting CD players, tuners, or other components with analog output, and the Analog Disc Input Board AD-10. The AD-10 contains a high-performance, high-gain phono equalizer, making it suitable for various phono cartridges (MM/MC) and allowing for the reproduction of analog records with high sonic quality. Internal DIP switches on the AD-10 board control MM/MC operation, MC input impedance, and subsonic filter on/off.
While the manual does not explicitly detail maintenance features, the design choices in the E-407 imply a focus on long-term reliability and performance. The use of high-quality components, such as the massive toroidal transformer, large filtering capacitors, and robust heat sinks, suggests a design intended to withstand the rigors of continuous operation and minimize the need for frequent servicing. The hermetically sealed, gold-plated relays for input switching are also indicative of a design aimed at preventing contact degradation over time, which is a common point of failure in audio equipment. The efficient thermal management provided by the large heat sink and the damping material in the transformer enclosure helps maintain optimal operating temperatures, contributing to the longevity of internal components.
General| Type | Integrated Amplifier |
|---|---|
| Power Output | 170 watts per channel into 8 ohms (stereo), 240 watts per channel into 4 ohms (stereo) |
| Total Harmonic Distortion (THD) | 0.05% |
| Input Sensitivity | 0.5mV (MC), 4mV (MM), 250mV (line) |
| Signal-to-Noise Ratio | 76dB (MC), 90dB (MM), 107dB (line) |
| Dimensions | 440 x 170 x 420 mm |
| Weight | 22.5kg |
| Speaker load impedance | 4 to 16 ohms |
| Output | Speakers |
