Усилители мощности стерео — Parasound HALO A51

The Parasound HALO A51 comes from the Halo range as a five-channel power amplifier whose circuits were drawn up by John Curl. Parasound presents it as a dedicated power amp for home theater systems that can add power to any audio-video receiver, and it carries THX Ultra2 certification. Parasound sells it for USD 5,000 and offers a warranty on parts and labor that runs three years.

Key specs that matter

In continuous operation from 20 Hz to 20 kHz with every channel loaded, each channel delivers 250 W into 8 ohms and 400 W into 4 ohms. Peak current reaches 60 A per channel. Power bandwidth runs from 5 Hz to 100 kHz at plus 0 and minus 3 dB at 1 W. THD stays below 0.2% at full power, and IM distortion is under 0.04%. Parasound quotes a slew rate above 130 V per microsecond, dynamic headroom above 1.5 dB and a damping factor above 1100 at 20 Hz. Noise sits 112 dB below signal, A-weighted, with the input shorted. Crosstalk between channels exceeds 78 dB at 1 kHz and 63 dB at 20 kHz. An input of 1 V produces 28.28 V at the output, matching the THX reference level. Input impedance is 47 kilohm unbalanced or 94 kilohm balanced.

Engineering and use context

The amplifier runs high-bias Class A/AB circuitry with a direct-coupled topology, so the signal meets neither capacitors nor inductors. A JFET input stage feeds a complementary MOSFET driver stage, which drives 40 beta-matched bipolar output transistors rated at 15 A and 60 MHz each. Power comes from a 2.2 kVA toroidal transformer whose secondary windings are separate for each channel, backed by 164,000 uF of filter capacitance. Output protection comes from DC servo and relay circuits. Inputs use discrete balanced circuits on XLR connectors alongside gold-plated RCA jacks, and a rear ground lift switch is fitted. The 4U chassis measures 445 mm wide, 194 mm high and 508 mm deep, or 178 mm tall without feet, weighs 36.3 kg and ships with handles for carrying plus an adapter for racks. The model is specified for 110 to 120 V mains.

Pairing

Parasound positions the A51 behind an AV receiver or surround processor, and automatic turn-on by a 12 V trigger or by an incoming audio signal lets it switch on together with the front end in home theater and multi-room systems. The 24k gold-plated 5-way terminals take the speaker cables for each of the five channels.

Alternatives

The Parasound HALO A52+ offers five channels in a 3U chassis rated at 180 W per channel into 8 ohms with all channels driven.