Усилители мощности стерео — Parasound HALO A31

The HALO A31 is a three-channel power amplifier in the Parasound Halo series, with circuitry by John Curl, high bias Class A/AB operation and THX Ultra2 certification. Its list price is USD 4,000, and the warranty runs three years for parts and labor.

Key specs that matter

Continuous output is 250 W RMS per channel into 8 ohm and 400 W RMS per channel into 4 ohm, from 20 Hz to 20 kHz with all three channels driven. Current capacity is 60 A peak per channel. Power bandwidth spans 5 Hz to 100 kHz within +0/-3 dB at 1 W. Total harmonic distortion is under 0.2 percent at full power and IM distortion under 0.04 percent. Slew rate is over 130 V per microsecond and dynamic headroom over 1.5 dB. Crosstalk between channels is better than 78 dB at 1 kHz and 63 dB at 20 kHz. Input sensitivity is 1 V for 28.28 V output, the THX Reference level. Input impedance measures 47 kohm unbalanced and 94 kohm balanced. Signal-to-noise ratio is 112 dB with the input shorted, IHF A-weighted, and damping factor exceeds 1,100 at 20 Hz. The chassis is 445 mm wide, 194 mm high with feet or 178 mm without, and 508 mm deep. It weighs 29.5 kg net and 35.8 kg packed. Standby draw is 1 W and maximum draw 1,800 W.

Engineering and use context

Signals pass by direct coupling, with no capacitors or inductors, from the input jacks to the speaker terminals through a JFET input stage and a complementary MOSFET driver stage. The output section has 24 beta-matched bipolar transistors rated at 15 A and 60 MHz, eight per channel. A 1.5 kVA encapsulated toroid transformer has independent secondary windings for each channel and feeds 98,400 uF of filter capacitance. A DC servo is fitted. Dedicated transistors monitor output stage current and open a relay if the load falls below 1 ohm or is shorted, thermal protection shuts the unit down until it cools, and front indicators show AC present, channel status and high temperature. Rear panel gain trims per channel allow up to 6 dB above THX Reference level, with the 12 o'clock position giving 29 dB.

Pairing

Each channel has unbalanced RCA and balanced XLR inputs, and heavy-duty 24k gold-plated 5-way terminals take the speaker cables. With three channels, the amplifier can drive the front left, center and right speakers of a home cinema. It switches on from the front button, by signal detection or through a 3.5 mm 12 V trigger jack, with a 2.5 mm adapter supplied, and a rack mounting adapter and carry handles are supplied with the 4U chassis.

Alternatives

The Parasound HALO A23+ is a two-channel Halo power amplifier rated at 160 W per channel into 8 ohm and 240 W into 4 ohm.