The Halo A 21+ power amplifier is a pinnacle of power and fidelity

The 21+ has two channels providing 250 watts per channel into 8 Ω, it delivers breathtaking audio performance. The high bias Class A/AB operation ensures accurate and detailed sound reproduction, while the stable operation into 2 Ω loads allows for versatility in speaker configurations. The direct-coupled design, free from capacitors in the signal path, preserves signal integrity and enhances transparency. With balanced XLR and unbalanced RCA inputs and A/B speaker terminals, it offers flexibility and compatibility. Experience pure power and fidelity with the Halo A 21+ power amplifier.

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 aluminium 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

Features

• 300 watts x 2 @ 8 Ω RMS, both channels driven
• 500 watts x 2 @ 4 Ω RMS, both channels driven
• 1000 watts x 1 @ 8 Ω, in bridged mode
• Circuitry designed by legendary John Curl
• High bias Class A/AB operation
• 60 amperes peak current per channel
• Stable with speaker impedance dips to 1.5 Ω
• Balanced inputs with discrete circuits
• CHK Infinium, custom 5-way speaker binding posts
• Gold-plated RCA input & loop output jacks
• Direct-coupled signal path, no capacitors or inductors
• DC Servo and relay protection circuits
• AC turn-on inrush surge protection with relay bypass
• JFET input stage, MOSFET driver stage
• 16 beta-matched 15 ampere, 60 MHz bipolar output transistors
• 1.3 kVA shielded toroid transformer w/ independent windings for each channel
• Independent power supplies for input stage, driver stage and output stage
• 108,000 µF filter capacitors for output stages
• Full power is rated all the way down to 5Hz for unrestricted low-end bass
• Harris hyper-fast soft-recovery bridge diode rectifiers
• Automatic turn-on by 12 V trigger or audio sensing
• 4 rack space chassis with rear carry handles
• Rack mount hardware is included

Specifications

• 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 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