The components I needed to choose for my first system were never in doubt: a turntable or record changer, an integrated amplifier, and a speaker. One of each, please, in those mono days.

Today, even in stereo, that trinity would be regarded as rather traditionalor, if you prefer, purist. Digital has exploded the range of source options and loudspeaker options. Yet amplifiers have not changed much in how and what they do. They take an analog voltage signal from the source, increase it, and back it up with enough current so that the output can power a relatively insensitive device, the loudspeaker. Amps still do the heavy lifting, and that includes today's popular class-A, class-AB, and class-D power amplifiers, none of which involve any digital operations. These being mature technologies, particularly for traditional-technologies amps, new power amplifiers inevitably compete with their predecessors as well as with their contemporaries. This is evident with the release of the new Parasound A 21+ stereo power amp ($3150), the successor to the A 21, which was originally launched in 2003.

Parasound was founded in 1981 by Richard Schram, and the company has been offering audio products under their own name as well as for OEM sales since then. Parasound has established close and long-term relationships, some spanning more than three decades, with contract manufacturers in Taiwan, which are responsible for the manufacturing. In 1988, Schram enlisted the services of circuit designer John Curl, and he brought along designers Carl Thompson and the late Bob Crump, forming a team whose work resulted in the development of Parasound's flagship Halo line. Halo products have consistently been praised by Stereophile and, over the years, their circuits and technologies have migrated into other Parasound products.

So: After the Halo A 21's 15 years in the marketplace, what has Parasound done to transform it into the A 21+? They offer a list:

 The power has been increased from 250W to 300W into 8 ohms, with comparable changes into smaller impedances.

 Power supply filter capacitance has gone from 88,000ÊF to 108,000ÊF.

 Signal/Noise is up from 112dB to 115dB.

 Total harmonic distortion at full power has been halved, from 0.2% to 0.1%; at normal listening levels it's claimed to be below 0.03%.

 Channel separation at 20kHz has been increased from 63dB to 70dB.

 The capacity of the transformer has been increased, from 1.2kVA to 1.3kVA.

 Partly as a consequence of the above, the amp got heavier: 71lb, compared to 60lb.

 Cosmetics were updated with aluminum endcaps and gold highlights.

 The same heavy-duty speaker terminals used in the JC 5 stereo power amp were added.

 Internal audio connections were upgraded to gold on gold.

 The automatic turn-on circuit was improved.

The performance-related improvementspower output, S/N ratio, THD, and channel separationare not huge, but they are appreciated; the increase in weight not so much. The cosmetic changes are subtle but positive, as is the improved auto turn-on circuit. What I really like are the brawny speaker terminals that you can tighten firmly without tools and, although not listed above, the modified rear-panel gain controls: On the A 21, the only calibration mark on each dual-mono gain control knob says "THX Reference." On the A 21+, there are clock-face calibration marks between "Min" (no sound) and "Max" (29dB for single-ended input, 35dB for balanced input). According to Parasound, the 3 o'clock setting means 20dB/26dB and the 12 o'clock setting means 10dB/16dB for single-ended/ balanced inputs, respectively. This is helpful for those of us who employ "gain staging" to minimize overall system output noise and who wish to match the settings on the two channels.

The front panel of the Halo A 21+ has a modern, clean appearance. There's a single On/Off button to the lower left, a high-temperature indicator to the lower right, and two small, blue LEDs between them: the indicator lights for the left and right channels. The rear panel, flanked by sturdy rack handles, has a set of four of the easiest-to-use and most secure multiway speaker binding posts I've ever encountered. To the left of the posts are the controls and connections for the various turn-on options; to the right are the main power switch and the IEC power receptacle. Across the top are two sets of connectors and controls, one per channel, with a bridged mono switch between them. Each set includes a balanced (XLR) input, an unbalanced (RCA) input, a switch to toggle between them, an unbalanced (RCA) loop-through output, and a gain control.

Since I already have in house the new amp's three-channel sibling, the Parasound A 31, I was comfortable installing the A 21+ in my system using the same XLR input cables and speaker cables, the latter with locking banana pins. The butterfly grips on the speaker terminals enticed me to try them, too, and, with them, hand tightening was easy and impressively secure. I connected the AC cable and clicked on the rear panel power switch; after a few seconds, a blue halo (!) glowed around the front panel On-Off button, indicating that the A 21+ was on standby. A push of said button was followed by the illumination of the dual-channel channel LEDs, and there was music.

Listening to the A 21+

I split my listening between the 35dB gain setting, using the output of the exaSound e38 multichannel DAC to drive the Parasound amp, and the 26dB gain setting, with the Audio Research MP1 multichannel preamplifier intervening. With the e38 directly connected to the A 21+, there was no audible noise from the system unless my ear was practically touching the tweeter of one of the Revel Ultima Studio2 loudspeakers. With the insertion of the somewhat noisier MP1 and the attendant lower gain setting on the A 21+, I could hear the hiss as far away as 4"! I listen from about 10' away, so I can live with that. In all situations, the A 21+ itself was dead silent with the sources turned off.