Parasound Halo A52+ 5-Channel Power Amplifier

Parasound Halo A52+ 5-Channel Power Amplifier

The Parasound Halo A52+ is a five-channel power amplifier from the Halo series, built to drive the front, centre and surround speakers of a home cinema system from a single chassis while leaving signal processing to a separate AV processor or receiver pre-outs. Its circuitry was designed by John Curl, and the amplifier is rated at 180 watts per channel into 8 ohms with all five channels driven, rising to 255 watts per channel into 4 ohms, which gives it the current reserve that demanding loudspeakers and large rooms require.

Key features

• Five channels of power: 180 W per channel into 8 ohms, all channels driven, 20 Hz to 20 kHz
• High current delivery: 45 amperes peak per channel, with 255 W per channel into 4 ohms
• John Curl circuitry: high-bias Class A/AB design with hand-matched JFET input stage
• Large power supply: custom 1.5 kVA encapsulated toroidal transformer and 100,000 uF filter capacitance
• Balanced and unbalanced inputs: five XLR and five RCA inputs, one pair per channel
• Flexible turn-on: manual, audio signal sensing or 12 V trigger operation
• Direct coupled design: no capacitors or inductors in the audio signal path

Power and current delivery

Multichannel amplifiers are often rated with only one or two channels working, which flatters the figures. The A52+ headline rating is with all five channels driven at once, across the full 20 Hz to 20 kHz band at under 0.05 percent total harmonic distortion. With two channels driven the output rises to 225 watts into 8 ohms and 350 watts into 4 ohms. A damping factor above 1,100 at 20 Hz, a slew rate above 130 volts per microsecond and dynamic headroom above 1.5 dB describe an amplifier intended to keep control of woofer cones during loud, complex passages rather than simply play loudly.

Circuit design and construction

The high-bias Class A/AB topology runs in pure Class A at lower levels before the second set of output devices takes over, a compromise intended to keep the smoothness of Class A without its heat and size penalties at full power. Each channel uses three pairs of beta-matched 15 amp, 60 MHz bipolar output transistors, fed by a 1.5 kVA toroidal transformer with independent secondary windings per channel. DC servo and relay protection circuits guard the speakers, and the signal path is direct coupled throughout.

Connections and system integration

Every channel offers both a balanced XLR input and an unbalanced RCA input, so the amplifier pairs equally well with a home cinema processor using balanced outputs or a receiver using pre-outs. Input impedance is 47 kilohms unbalanced and 94 kilohms balanced, with 29 dB of gain. Speaker connection is by heavy-duty gold-plated five-way binding posts. Turn-on can be manual, triggered by an incoming audio signal, or controlled by a 12 V trigger from the processor, with a trigger output provided to pass the command on to further equipment.

Measured performance

Frequency response extends from 5 Hz to 100 kHz within 3 dB, and sits within 0.3 dB across the audible band. Signal-to-noise ratio is above 112 dB A-weighted with the input shorted, interchannel crosstalk is above 78 dB at 1 kHz, and distortion at typical listening levels is below 0.03 percent. The 3U chassis measures 437 x 149 x 508 mm including feet and weighs 25 kg, and it can be rack mounted with the optional HRA 3 kit, suiting both furniture placement and equipment racks in dedicated cinema rooms.

As the power stage of a separates-based cinema system, the A52+ offers a single, consistent amplifier character across all five main channels, with enough current in reserve for low-impedance speakers and high playback levels.