Интегральные усилители — Accuphase E-700

The E-700 is an integrated stereo amplifier working in Class A, made by the Japanese company Accuphase. Its output stage runs power MOS-FETs in pure Class A, and the signal stays fully balanced from the input terminals through to the speaker outputs. In the current Accuphase range of Class A integrateds it sits beneath the E-800S.

Key specs that matter

Rated linear output is 35 W per channel into 8 ohm, 70 W into 4 ohm and 140 W into 2 ohm, all with both channels driven from 20 Hz to 20 kHz. Rated distortion is 0.03 percent into 4 to 16 ohm and 0.05 percent into 2 ohm. At rated output the line input response is 20 Hz to 20 kHz within +0/-0.5 dB, while at 1 W it extends from 3 Hz to 150 kHz, +0/-3 dB. Signal-to-noise ratio for the line inputs is 102 dB at rated output, and input impedance is 20 kohm unbalanced and 40 kohm balanced. Main In connections allow the preamplifier section to be bypassed. Damping factor is specified at 1,000. Connections comprise two balanced XLR line inputs and five unbalanced RCA line inputs. The chassis measures 465 x 191 x 428 mm and weighs 24.9 kg.

Engineering and use context

In each channel there is a four-fold parallel push-pull arrangement of power MOS-FETs biased in Class A, which keeps every output device conducting over the whole waveform. The power amplification stage is built as an instrumentation amplifier, a topology Accuphase applies to its balanced designs. Level is set by a balanced AAVA volume control, the company's own approach in which gain is adjusted through current addition rather than a variable resistor in the signal path. Its position is read by a high-accuracy, high-rigidity volume sensor. Current for the audio circuits comes from a high-efficiency toroidal transformer paired with large filtering capacitors. Protection circuits use MOS-FET switching, so no relay contacts that can wear sit in the speaker line. Because Class A output devices idle at high current, the unit dissipates substantial heat even without a signal, which accounts for the weight and heatsink area of the case.

Pairing

Low-impedance loudspeakers stay within the amplifier's specified operating range, while the modest Class A output suits more sensitive designs when high levels are wanted. Sources fitted with XLR outputs connect to the balanced inputs and keep the signal balanced to the output stage.

Alternatives

The Accuphase E-800S is the larger Class A integrated in the range, with six-fold parallel output devices and 50 W into 8 ohm.