Parasound HALO A51 - AV Receivers
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Parasound HALO A51


Parasound HALO A51



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Parasound HALO A51 - 5 (Multi) Channel Power Amplifier

The A51 is a THX Ultra2-certified, five-channel amp churning out 250 watts per channel into eight ohms and 400 watts per channel into four ohms. The A51 is a high-bias Class A/AB operating amp in a direct-coupled design with no capacitors or inductors in the signal path, powered by a massive toroid transformer. The A51 uses a MOSFET driver stage complemented by a JFET input stage. The A51 features both balanced and unbalanced input connections, as well as 24-karat gold five-way binding posts. It features large heat sinks along both the right and left sides, as well as down the centre of the rear panel, separating the inputs from the binding posts to dissipate some of that class A heat. The A51 has a 12-volt trigger, as well as a detachable power cord, and comes standard with rack-mounting equipment, which is almost unheard of with an amp costing as little as the A51.


Parasound Halo A23 2 Channel Amplifier
  • 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
  • Parasound 2 year parts, 2 years labour warranty

Audioholics, October 2004
"The A 21 and A 51 amplifiers are both loaded with usable features above and beyond most other amplifiers in today's market." "The Parasound A 51 is more than capable of driving any speaker load in even the most demanding home theater systems." "The linearity of this amplifier is excellent at any power level it is operating in, and its freedom from audible noise and distortion makes it a true winner!" "The Parasound Halo A 21 and A 51 are top rate amplifiers at a great value. Parasound seems to have attended to every aspect of their design including the excellent build quality internally and externally matched with great looks." Overall Rating: 5/5 Stars - Ken Stein and Steve Dellasala
Home Cinema Choice (UK), October 2004
"The processor (C 1) offers enveloping surround sound processing, and the power amplifier is muscular. It has a hint of warmth, but nothing that suggests overhang, and the treble is unusually refined." "Indeed, I'd rate the A 51 as one of the most transparent power amplifiers in its class. It has genuine power and authority, and delivers the kind of visceral kick that makes action films swing along with panache." Five Stars - Alvin Gold
Stereophile Guide to Home Theater, March 2004
AAA Recommended Component - "I expected the A 51 to sound good. What I wasn't prepared for was how good it sounded right out of the box. Its midrange was totally seductive, its soundstaging and imaging abilities in the same league as some of the best gear I've ever heard at any price."
Home Theater Buyers Guide, 2004
Featured component in Stepping Up Your System article. "Sky is the limit" system.


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 < 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 Level
Input impedance 47 k Ω unbalanced
S/N ratio 112 dB, input shorted, IHF A-weighted
Damping factor > 1100 at 20 Hz
Voltage 110V - 120V
Dimensions 17-1/4" w x 7-5/8" h x 20" d, 7" h without feet
Net weight 80 lb.


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