Усилители мощности стерео — Parasound HALO A21+

The HALO A21+ is a Halo line two-channel power amplifier by Parasound, with a John Curl circuit and high bias Class A/AB operation. Parasound describes it as a refinement of its John Curl power amplifier design aimed at current systems, combining high output with simple operation. Parasound lists the model as discontinued and no longer in production.

Key specs that matter

With two channels working, the amplifier delivers 300 W per channel into 8 ohm and 500 W per channel into 4 ohm with both channels driven at 0.1 percent THD. Bridged, it gives 1,000 W into 8 ohm, a figure also quoted at 0.1 percent THD, and Parasound does not recommend bridged operation into 4 ohm. Peak current capacity is 60 A per channel and slew rate is above 130 V per microsecond. Frequency response runs from 5 Hz to 100 kHz within +0/-3 dB and from 20 Hz to 20 kHz within +0/-0.25 dB. THD is below 0.1 percent at full power and below 0.03 percent at typical listening levels, and IM distortion is below 0.04 percent. Noise sits more than 115 dB below the signal IHF A-weighted and more than 110 dB unweighted, and crosstalk is better than 80 dB at 1 kHz and 70 dB at 20 kHz. Input impedance is 33 kohm unbalanced and 66 kohm balanced, with total gain of 29 dB. Damping factor exceeds 1,100 at 20 Hz. The chassis measures 448 mm wide, 181 mm high without feet and 508 mm deep, and weighs 32.2 kg net or 39.9 kg packed for shipping.

Engineering and use context

The direct-coupled path is free of capacitors and inductors, using a JFET front end and MOSFET drivers that feed 16 beta-matched output transistors. Balanced inputs are built with discrete circuits. A 1.3 kVA shielded toroid transformer has independent windings for each channel and feeds 108,000 uF of filter capacitance. Power draw is 1 W in standby, 160 W at idle, 300 W typical and 1,400 W maximum.

Pairing

Parasound presents the balanced XLR and RCA inputs and the flexible bridging as making the A21+ suitable for both stereo and home theater systems, where a bridged unit can serve as a single high-power channel. The unit can switch on automatically through a 12 V trigger or when it senses an audio signal. The four-rack-space chassis has carry handles, and rack mount hardware is included.

Alternatives

The Parasound JC5 is a current stereo power amplifier rated at 400 W per channel into 8 ohm and 600 W into 4 ohm.