Усилители мощности стерео — Accustic Arts AMP IV

The AMP IV is a stereo power amplifier from Accustic Arts of Germany, which the company calls its bestseller and has now brought to its fifth generation. It is a dual-mono reference design made by hand, with a completely separate supply for each channel inside a single 340 x 470 x 440 mm case, the same enclosure size that holds the MONO IV monoblock. US pricing has been USD 40,990 with chrome trim and USD 42,990 with gold trim.

Key specs that matter

At 0.1 percent THD+N the rated power per channel is 400 W into 8 ohm, 620 W into 4 ohm and 810 W into 2 ohm, and 2 ohm is the minimum load. Voltage gain is 25.0 dB, lower than the 30.0 dB of the MONO IV and of the larger AMP VI. Frequency response runs from 10 Hz to 50 kHz within +0 and -0.5 dB at 10 W. THD+N is 0.003 percent at 1 kHz and 10 W into 4 ohm, signal-to-noise ratio is 103 dBA, 7 dB better than the figure quoted for the AMP VI, and crosstalk between channels is 109 dB at 1 kHz. Input resistance is 16 kohm on XLR and 15 kohm on RCA. The quiescent current in the output stage is about 300 mA and idle power draw about 120 W. The amplifier weighs close to 44 kg, and its flight case weighs 12 kg more.

Engineering and use context

The circuit runs in class AB with a MOS-FET current mirror layout, and 20 selected MOS-FET transistors share the output duties across the two channels. Each channel has its own magnetically shielded and encapsulated toroidal transformer, and the combined reservoir capacitance is about 160,000 uF, using capacitors made in Germany. The damping factor is specified as very high, and a switchable damping factor linearization lets the owner turn that function on or off. Protection against clipping and HF oscillation is built in, together with a switch-on current limiter. The case is a stiff, resonance-optimised block of aluminium with a polished and chromed brass inlay on the front.

Pairing

Because it is rated into very low impedances, the AMP IV can run loudspeakers with low impedance dips without a second chassis. Source selection between the XLR and RCA inputs is made with a rear switch, and WBT speaker terminals allow bi-wiring or, with two units, vertical bi-amping. The modest gain works well with preamplifiers that have a high output voltage.

Alternatives

The Accustic Arts AMP VI is a bigger two-channel model from the same range with 40 output transistors and rated above 950 W per channel into 8 ohm.