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Parasound A 51 Power Amplifier (Each)

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Parasound A 51 power amplifier combines raw power with elegant circuit design. Designed by legendary audio guru John Curl in collaboration with CTC Builders, the Halo brings uncompromising audiophile performance to home theater.

THX Ultra 2 certification ensures movie-house quality sonics, but the Halo surpasses this critical benchmark by delivering Parasound-quality sound derived from the ultra-high-end Parasound JC-1 400-watt mono amp. Matched JFET inputs, MOSFET drivers, and high-current bipolar outputs contribute to its exceptional performance.


  • Circuitry designed by legendary John Curl
  • THX Ultra2 certified
  • High bias Class A/AB operation
  • Balanced inputs with discrete circuits and XLR connectors
  • Direct Coupled – no capacitors or inductors in signal path
  • Complementary MOSFET driver stage and JFET input stage
  • 40 beta-matched 15 amp, 60 MHz bipolar output transistors
  • 2.2 kVA encapsulated toroid power transformer with independent
  • secondary windings for each channel
  • 164,000 μF power supply filter capacitance
  • DC Servo and relay protection circuits
  • AC present, channel status, high temperature indicators
  • Heavy-duty 24k gold-plated 5-way speaker terminals
  • Gold-plated RCA input jacks; ground lift switch
  • Auto turn-on by 12v trigger or audio signal
  • 4u Chassis, carry handles, rack mounting adapter included


  • Continuous power output:
    250 watts RMS x 5, 20 Hz – 20 kHz, 8 Ω, all channels driven
    400 watts RMS x 5, 20 Hz – 20 kHz, 4 Ω, all channels driven
  • Current capacity:
    60 amperes peak per channel
  • Power bandwidth:
    5 Hz – 100 kHz, +0/-3 dB at 1 watt
  • Total harmonic distortion:
    < 0.2 % at full power
  • IM distortion: balanced 16 V rms: 
    < 0.04 %
  • Slew rate:
    > 130 V/µsecond
  • Dynamic headroom:
    > 1.5 dB
  • Interchannel crosstalk:
    > 78 dB at 1 kHz;
    > 63 dB at 20 kHz
  • Input sensitivity:
    1 V for 28.28 V, THX Reference Lev
  • Input impedance:
    47 k Ω unbalanced; 94 k Ω balanced
  • S/N ratio:
    112 dB, input shorted, IHF A-weighted
  • Damping factor:
    > 1100 at 20 Hz
  • Voltage:
    110V – 120V
  • Dimensions:
    17-1/2″ w x 7-5/8″ h x 20″ d, 7″ h without feet
  • Net weight: 80 lb.


The A 51 boasts balanced inputs with discrete circuits and XLR connectors. Beautifully implemented high-bias Class A / AB operation makes the most of an impressive 250-watt-per-channel power output at 8 ohms and 400-watts-per-channel at 4 ohms. The 2.2 kVA encapsulated toroidal power transformer with independent secondary windings for each channel and 164,000 µF power supply filter capacitance delivers an impressive current capacity of 60 amps per channel. The direct-coupled design uses no capacitors or inductors in signal path. The complementary MOSFET driver stage relies on the firepower of 40 beta-matched 15 amp, 60 MHz bipolar output transistors and works in combination with a JFET input stage.


Like all the other amps in the Halo product series, the A 51 has Parasound‘s exclusive bias circuit, which permits the amplifier to sound perfect from the instant it’s turned on, rather than having to wait for bias to gradually build up as the amp warms up over time. Very high bias allows greater Class operating range than others. Even Halo’s implementation of its automatic turn-on feature is exceptional. Special relays bypass the AC “soft start” circuitry after it’s done its job for the purest AC and the purest sound.


AC present, channel status, and high temperature indicators team up with DC Servo and relay protection circuits to keep this powerhouse running safely at peak performance for years of reliable service. Auto turn-on by 12-volt trigger or audio signal simplifies home theater and multi-room operation. Other features include heavy-duty 24k gold-plated 5-way speaker terminals, gold-plated RCA input jacks, and a rear-panel ground lift switch.




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