Power Amplifiers

Parasound Halo A 31 Three-Channel Power Amplifier


Design and Setup of the Parasound Halo A 31 Power Amplifier

Offering the same 250 WPC into 8 ohms and 400 WPC into 4 ohms that the A21 and A 51 do, the A 31 makes an ideal mate for your front three speakers without having to spend money on extra power for surround channels that may not need it. With the balanced inputs it also allows you to keep the amplifier close to the front channels, allowing for shorter, more convenient speaker cable runs and longer runs of the balanced interconnects that are less prone to picking up noise.

Looking at the specifications for the A 31, it is effectively a three-channel version of the Halo A51 amplifier that has been in their line for years. Each channel has the same number output transistors and filter capacitance, though there is a bit larger toroid power transformer in the A 31 on a per-channel basis. Using the same John Curl designed amplifier circuit that is in the A51 is a good thing, as the A51 has been thoroughly analyzed and tested over the years and always has performed well.

The silver front panel of my unit looked quite nice, with a single power button up front for controls, with lights to indicate power and channel status. The rear contains all of the inputs and outputs for the A 31, as well as a set of handles to help you move it into position. Each channel has XLR and RCA inputs, with a switch to change between the two, and an adjustable gain knob. By default it comes at the THX reference level of 28.28 V of output for 1 V of input, but you can adjust this by up to +6 dB per channel to level match amplifiers in your system that might run higher than the THX standard.

A 12V trigger input allows you to set the amplifier to turn on based off the trigger, or it can power on when it sees an input signal, or from the front power switch if you want the manual option. Both sides of the A 31 are covered by large heat sinks to dissipate all of the heat given off by the amplifier, and there is no fan to introduce noise while in operation. Rated for 250 WPC into 8 ohms, and 400 WPC into 4 ohms, the first 5 watts of the Halo A 31 are actually Class A before it crosses over into Class AB. With most listening actually taking place at 5 watts or less, this offers sonic benefits to the user with lower distortion and odd-order harmonics.

I used the unbalanced RCA inputs with my Marantz AV7005 processor, and the 12V trigger input for controlling power. The 12V trigger out was used for an Emotiva UPA-5 to power the surround channels.