Parasound A51, open box new. Hooked up and played briefly and reboxed.
Raw Power Meets Elegant Circuit Design
Barry Willis praises the Parasound A51 for its "harmonic rightness" in Stereophile Guide to Home Theater
for October 2003. "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... With music, the A51 radiated sweetness and
light. With action films, it rained thunder and lightning. There aren't
many amplifiers that can so effortlessly cover both ends of the sonic
The Jan / Feb. 2004 Top Choice Awards issue of DVD ETC.
magazine praises the Halo A51 multichannel amp and the Halo C2 surround
sound processor for their "sonic performance, auto calibration,
complete feature set, programmability and upgradeability."
Uncompromising Audiophile Performance
Parasound's five-channel Halo A51 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.
Class A / AB Operation and Impressive Firepower
The A51 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.
"Instant" Warm-up Feature
Like all the other amps in the Halo product series,
the A51 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.
And That's Not All…
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.
- Circuitry designed by John Curl
- THX Ultra 2 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 toroidal 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, carrying handles, rack mounting adapter included
- Power output: 250 watts RMS x 5 continuous, 20 Hz - 20 kHz at 8 ohms; 400 watts RMS x 5 continuous, 20 Hz - 20 kHz at 4 ohms
- Current capacity: 60 amps peak per channel
- Frequency response: 5 Hz - 100 kHz, +0/-3 dB at 1 watt
- Total harmonic distortion: <0.2% at full power, <0.03% at typical listening levels
- IM distortion: <0.04%
- TIM: Unmeasureable
- Signal-to-noise ratio: >112 dB, input shorted, IHF A-weighted; 102 dB, input shorted, unweighted
- Dynamic headroom: >1.5 dB
- Interchannel crosstalk: >78 dB at 1 kHz, >63 dB at 20 kHz
- Input impedance: unbalanced 47 K ohm, balanced 94 K ohm
- Input sensitivity (for 28.28 V output into 8 ohm): unbalanced 1 V, balanced 1 V per leg
- Slew rate: >130 volts per microsecond
- Damping factor: >1100 at 20 Hz
- DC trigger requirements: +9 VDC to +12 VDC, 2 mA
- Audio trigger requirements: 50 mV AC - 250 mV AC
- Power consumption: standby, 25 watts; full power into 4 ohms, 3000 watts
- Weight: 77 lbs.
- Shipping weight: 92 lb.
- Dimensions: 17.5" wide, 20" deep, 7" high (7.625" with feet)
- Manufacturer's limited warranty: 5 years parts, 5 years labor