Outrageously Good Transparency, Focus, and Insight: 300Wpc Parasound A 21+ Power Amplifier Features John Curl-Designed Circuitry, Class A/AB Operation, World-Class Parts
You seldom come across audio equipment that long-time high-end authority Stereophile deems "impossible to fault," but when the gear is as special as the Parasound A 21+ stereo power amplifier, you soon realize such praise comes without any hint of hyperbole. Playing with beguiling levels of transparency, focus, and insight, and offering a high-value quotient few other designs can even come close to nearing, A 21+ delivers a whopping 300 watts into eight ohms (500Wpc into four ohms) and 60 amperes of peak current per channel – enough to handle with kid gloves nearly any speaker in the land. Stable with speaker impedance dips to 1.5 ohms and touting circuitry designed by the iconic John Curl, A 21+ is an exceptional – and exceptionally musical – performer.
For starters, its full power is rated way down to 5Hz, allowing for incredibly deep and fully unrestricted bass response. A 21+'s high-bias Class A/AB topology (supplying six watts of Class A power per channel) features a direct-coupled signal path (free of capacitors and inductors) and, remarkably, independent power supplies for the JFET input stage, MOSFET driver stage, and output stage. Built like the proverbial brick house, the 71-pound gentle giant comes loaded with audiophile components and over-engineered parts. A 1.3kVA shielded toroidal transformer with independent windings for each channel, 16 beta-matched 15-ampere/60MHz bipolar output transistors, 108,000uF filter capacitors for the output stages, and Harris soft-recovery bridge diode rectifiers all account for its distinguished performance.
Seen head-on, A 21+ looks sleek, modern, and classic in both black and silver, with refined aluminum end caps and gold highlights. On the clean back panel, you'll find a pair of balanced XLR inputs with discrete circuits, gold-plated RCA inputs and loop outputs, and CHK Infinium five-way speaker binding posts. Gain knobs for both left and right channels and multiple turn-on options (including auto-on via 12V trigger or audio sensing) are also here. The rack-mountable A 21+ even includes rack hardware, DC servo and relay protection circuitry, and AC turn-on in-rush surge protection.
True to Parasound's "measure twice, cut once" philosophy, A 21+ arrives ready to impress. The measured specifications – a staggering 115dB signal-to-noise ratio, 0.1% THD at full power, 70dB channel separation at 20kHz, less than 0.04% IM distortion – are alone incredible. If you need more convincing, just look at the reviews – or arrange for a risk-free audition in your own home. A five-year manufacturer warranty and our 100% Music Direct Satisfaction Guarantee will do the rest.
"The Parasound A 21+ is remarkably powerful, transparent and quiet. As such, it imposes no constraints on one's desire to listen through it to the recorded performance or to experience the size, weight, and dynamics of the original event."
– Kalman Rubinson, Stereophile
"With its high-quality chassis, thoughtful circuit design, and excellent sound quality, the A 21+ offers an impressive value proposition. Those shopping for a stereo amplifier in this price range should give the A 21+ serious consideration."
– Dylan Seeger, Home Theater Review, five-star review
"The A21+ represents a new unparalleled value in amplifier performance. If your amplifier budget dictates $2000 USD on an amplifier, save a little longer and buy the A21+. If the amplifier budget is endowed to the order several thousand or more, pick up the A21+ and a pair of loudspeakers that will allow you to hear what this amp is capable of. It would be difficult to get more amplifier without pursuing a home equity loan, or at least a small automobile loan."
– Michael Zisserson, Positive Feedback
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
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 %
> 80 dB at 1 kHz
> 70 dB at 20 kHz
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
> 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)
Standby: 1 Watt
Idle (no music playing): 160 Watts
Typical Listening levels: 300 Watts
Maximum: 1400 Watts
Dimensions (WHD): 17-5/8" x 7-1/8" x 20"
Weight: 71 lbs.
User Manual (PDF, 3.6 MB)