Parasound A31 Halo 3 Channel Power Amplifier (Mint Condition)

Description

The A31 utilizes the same chassis as its fellow multi-channel and stereo siblings (including the JC1), measuring 17.25 inches wide by nearly eight inches tall (with feet) and just over 19 inches deep. It's hefty, too, weighing a respectable but not unmanageable 65 pounds. The front panel features Parasound's logo on top with three small indicator lights below the THX logo and a small backlit power button resting in the far left corner. The sides of the A31 are adorned with heat sink fins that feature rounded edges, so as not to cause any physical harm to the customer or installer charged with moving the A31 into its final position. Around back, you'll find a host of input/output options, as well as a few features not commonly found on most amplifiers, budget or otherwise. Moving from left to right the first thing you'll notice are the A31's massive metal rack handles. Just inside the left handle are the A31's "Turn On Options," which include an auto/manual power switch and a 12-volt trigger. The manual switch allows you to set the A31's auto power up feature to either auto (which has a sensitivity dial), manual (using the front-mounted power button) or via a 12-volt trigger. There is even a loop out option for daisy-chaining several amps together if you so desire. Each of the channel inputs are neatly arranged, well spaced and labeled 1, 2 and 3, respectively. Each features XLR as well as RCA input options that are selectable via a small toggle switch. To the left of the input options rests a gain knob that gives you control, plus or minus 6dB off normal or THX reference, to help level match the A31 to other amplifiers - presumably ones that fall outside of the Halo lineup of products. This is a decidedly pro feature, one I'll discuss in a moment. Below the input options rest a pair of five-way binding posts, one pair for each channel. Along the far right side of the back panel rests a large master on/off switch as well as a standard AC power receptacle.
Behind the scenes, the A31 is quite a brute, churning out a healthy 250 watts per channel into eight ohms and 400 watts per into four. The A31 is THX Ultra2-certified as well. The A31's internal circuitry was designed by none other than John Curl, a longtime Parasound collaborator and designer extraordinaire, with more than a few hits to his name. The A31, like all Halo-branded amplifiers, is a high-bias Class A/AB amplifier, meaning the first few watts - in this case seven - are delivered in pure Class A fashion before switching over to AB status. The signal path is direct-coupled, meaning no capacitors or inductors are used anywhere in the signal path, and is capable of full power output down to 5Hz. The A31 employs matched pairs of JFETs for its input/pre-driver stages and matched pairs of MOSFETS in its driver stage. It also utilizes eight beta-matched, 15-amp 60Hz output transistors for each channel. The A31 plays host to a large encapsulated toroid transformer (1.5 kVA) with separate, independent windings for each of its three channels.
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