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

All 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

·         Available in silver or black

 


  [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 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)
• Shipping Weight
  88 lb. (39.9 kg)
• Power Requirement
  Standby: 1 Watt
  Idle (no music playing): 160 Watts 
  Typical Listening levels: 300 Watts
  Maximum: 1400 Watts