Усилители мощности стерео — Analog Domain The Isis M75P

The Isis M75P is the two-channel power model in the Isis series by Analog Domain Audio GmbH, the German maker that Angel Despotov founded in Munich at the start of 2010. It carries the same power amplifier section as the M75D integrated model but omits the preamplifier, volume control and headphone stage, so it is meant to follow an external preamplifier. The Dutch price in 2018 was EUR 19,600, and a Mk2 version followed later.

Key specs that matter

In stereo operation the M75P gives 2 x 250 W into 8 ohm and 2 x 400 W into 4 ohm. Bridged as a monoblock it provides 500 W into 8 ohm and 1,000 W into 4 ohm, with a damping factor above 500 in that mode. THD+N is below 0.001% and the noise floor below 25 microvolts, lower figures than those of the integrated sibling. The frequency response extends from 5 Hz to 50 kHz. Input impedance is kept fairly low, around 5 kohm differential, to reduce noise. Connections are one balanced XLR input, one unbalanced RCA input and a set of speaker terminals that take spades or banana plugs. Net weight is 25 kg, and 35 kg packed. Black and silver finishes were offered.

Engineering and use context

Its circuit uses the Excalibur topology, in which the output devices operate as common emitter stages rather than the usual common collector followers. This removes local current feedback from the signal path and gives the output very low internal resistance. Analog Domain uses its proprietary DXDrive bias control to make the topology stable, since common emitter output stages would otherwise be exposed to thermal runaway. The output stages run in class AB with sliding bias, while the rest of the electronics is biased in class A. Buffered loop-through outputs on the analogue inputs feed a second amplifier for bi-amping. When bridged, the M75P becomes a fully differential amplifier, and the gain of both halves is matched within 0.1%. Idle power consumption is about 22 W, which reflects the design goal of keeping heat low. The adjustable feet can be levelled or removed completely, and a front display reports operating status. Analog Domain states a design life of at least 25 years and grants a transferable ten-year warranty.

Pairing

A preamplifier with balanced output fits the XLR input, and the M75D integrated model can also feed it as a preamplifier through its five-pin DIN pre-out. Two M75P units bridged as monoblocks suit loudspeakers that need more than the stereo rating.

Alternatives

Analog Domain lists no other two-channel power amplifier in its current range.