Parasound Halo A 21+ Stereo Power Amplifier

Parasound Halo A 21+ Stereo Power Amplifier - Parasound

Parasound decided to update their already brilliant A 21 power amplifier which had become a staple for their brand for over 10 years. With the assistance of legendary Audio Designer John Curl, they’ve created a beautiful and powerful successor to the A21, The A21+ stereo power amplifier.

Circuitry Designed By John Curl:
Parasound design consultant John Curl has been a legend among audiophiles and electronic engineers for decades. He pioneered measurements to correlate musical accuracy with the materials used in parts, worked with world-class touring companies, has designed highly coveted audio classics, including the original Mark Levinson JC-2, Denneson JC-80, Vendetta Phono Preamplifier, and CTC Blowtorch preamplifiers; master recorders for Wilson Audio and Mobile Fidelity; and the mixing consoles used in live concerts by The Grateful Dead and the Montreux Jazz Festival in Switzerland.

As Parasounds featured amplifier designer since 1990, he has created many products that have earned Parasound worldwide acclaim, including the Parasound Halo JC 1, JC 2 and JC 2 BP, JC 3, JC 3+ and JC 3 Jr. and JC 5. John is particularly proud of what he and Parasound have accomplished together: “The circuits I design for Parasound are extremely sophisticated and are typical of products that are far more expensive. I can’t think of any other audio products that offer nearly as much bang for the buck.”

Parts Selection:
Every part within the A 21+ is carefully chosen for its accuracy and reliability. Metal film resistors with 1% tolerance are selected for their precision and because their values don’t drift as they heat up during operation.

Polypropylene and mica capacitors are used extensively for their superior linearity and low dielectric absorption. Semiconductors are selected for superior performance in their specific roles in the circuit. Gold has the best conductivity of any metal, so Parasound use high quality gold-plated input connectors and speaker terminals. The double-sided circuit boards are FR4 glass epoxy for long-term durability. The chassis is made of heavy gauge steel to safely house the internal circuitry. This attention to detail when selecting parts makes the difference between a very good amplifier and an outstanding amplifier.

The Power Supply:
The heart of the power supply is a 1.3kVA toroid power transformer, chosen for its efficiency, low hum field, and high power rating. Encapsulating this massive power transformer in an epoxy-filled steel canister assures ultra-quiet performance. The A 21+ power transformer employs multiple independent secondary windings so that each amplifier channel has its own power supply, assuring more than ample DC voltage at all times and under all conditions. It also reduces inter-channel crosstalk that can blur the sound and impair the correct sense of where instruments, dialogue and effects are positioned.

Features:

Changes from the original A 21→A 21+

• 250 → 300 Watts (8Ω)
• 400 → 500 Watts (4Ω)
• 750 → 1000 Watts (bridged)
• Filter cap: 88,000 uF → 108,000 uF
• S/N: 112dB → 115 dB
• THD (at full power): 0.2% → 0.1%
• Crosstalk (20kHz): 63dB → 70dB
• Transformer size: 1.2 kVA → 1.3 kVA
• Weight: 60 LB → 71 LB
• Refined Halo cosmetic with aluminum end caps & gold highlights
• Updated rear panel with heavy duty speaker terminals from JC 5
• Upgraded internal gold on gold audio connections
• Updated auto turn on circuit

Specs

• Power Output – Stereo Mode (0.1% THD): 300 watts x 2, 8 Ω both channels driven, 500 watts x 2, 4 Ω both channels driven
• Power Output – Bridged Mode (0.1% THD): 1000 watts x 1, 8 Ω, Bridged 4 Ω operation is not recommended
• Power measurement parameters are at 120 VAC: 0.1% THD, RMS continuous power, full audio band (20 Hz - 20 kHz)
• Current Capacity: 60 amps peak, per channel
• Slew Rate: > 130 volts per microsecond
• Frequency Response: 5 Hz - 100 kHz, +0/-3 dB, 20 Hz - 20 kHz, +0/-0.25 dB
• Total Harmonic Distortion (THD): < 0.1 % at full power, < 0.03 % at typical listening levels
• IM Distortion: < 0.04 %
• TIM: Unmeasurable
• Inter-channel Crosstalk: > 80 dB at 1 kHz, > 70 dB at 20 kHz
• Input Impedance: Unbalanced: 33 kΩ , Balanced: 66 kΩ,(33 kΩ per leg)
• Total Gain: 29 dB
• Input Sensitivity for 28.28 V Output into 8 Ω: Unbalanced: 1 V, Balanced: 1 V per leg
• S/N Ratio: > 115 dB, input shorted, IHF A-weighted, > 110 dB, input shorted, unweighted
• Damping Factor: > 1100 at 20 Hz
• DC Trigger Requirements: +9 Vdc to +12 Vdc, 5 mA
• Audio Trigger Requirements: 2 mV - 10 mV
• XLR Pin Identification: 1 = Ground (Shield), 2 = Positive, 3 = Negative (Return)

Dimensions

• Width: 17-5/8" (448 mm)
• Height without feet: 7-1/8" (181 mm)
• Height with feet: 7-3/4" " (197 mm)
• Depth: 20" (508 mm)
• Depth with cables: 21-1/2" (546 mm)
• Net Weight: 71 lb. (32.2 kg)
• Power Requirement: Standby: 1 Watt, Idle (no music playing): 160 Watts,Typical Listening levels: 300 Watts, Maximum: 1400 Watts

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