Усилители мощности стерео — Analog Domain The Isis M75D

The Isis M75D belongs to the Isis two-channel series from Analog Domain, the Munich-area company founded in early 2010 by Angel Despotov, and it is an integrated amplifier rather than a pure power amplifier - it combines a stereo power section with a preamplifier, volume control and remote. The same power stage appears in the M75P power amplifier. In 2018 the M75D was priced at EUR 21,750 in the Netherlands, and the later Mk2 version was listed at EUR 20,990 including VAT in Germany.

Key specs that matter

Continuous output is 250 W into 8 ohm and 400 W into 4 ohm per channel, and in bridged mono mode one unit delivers 500 W into 8 ohm. Peak current is 50 A. THD+N stays below 0.002% into 8 ohm at rated power in a 20 kHz bandwidth, the noise floor is under 35 microvolts, and signal to noise ratio exceeds 120 dB. The bandwidth runs from 5 Hz to 50 kHz. Damping factor is over 1000, measured at 1 kHz into 4 ohm. Inputs comprise two balanced XLR pairs with 20 kohm impedance and two RCA pairs at 10 kohm, the RCA inputs with an optional +8 dB gain, and maximum input level is 10 Vrms. The case measures 440 mm wide, 454 mm deep and 123 mm high, and the amplifier weighs about 25 kg.

Engineering and use context

Analog Domain calls its output topology the Excalibur circuit - the output transistors work in a common emitter configuration instead of the usual emitter follower, giving near-zero internal resistance and unrestricted current delivery. Its DXDrive bias control keeps this arrangement from thermal runaway. All circuitry runs in class A except the output stages, which work in class AB to limit heat, and a class G supply switches between separate rails for low and high power. The Mk2 added the supply management of the larger monoblocks, where the rail voltage follows the output signal, as well as a thermal circuit breaker at the mains inlet and a rebuilt preamplifier module. Volume is set by a discrete resistor matrix with opto-coupled MOSFET relays in 0.75 dB steps down to -96 dB, and output impedance stays constant at every setting. An automotive-grade microcontroller handles control and switches off with its clock when idle. Standby draw is under 2 W and idle draw about 22 W. The chassis is machined, with latticed top and bottom plates and no visible screws.

Pairing

Its peak current rating means low-impedance loudspeakers are no problem, and the M75D drives 2 ohm loads. A built-in headphone output with a limiter indicator serves private listening, and a five-pin DIN pre-out and power-in loop links it to a second amplifier when bi-amping.

Alternatives

The Analog Domain M75A is the other integrated version in the Isis series, replacing the stepped remote-controlled attenuator with a linear analogue volume control operated by hand.