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Parasound HALO A 23 Stereo Power Amplifier Print E-mail
Sunday, 01 December 2002
Article Index
Parasound HALO A 23 Stereo Power Amplifier
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ImageParasound has been producing high-quality audio components at a reasonable price for over 20 years. The new HALO line represents a dramatic improvement in both appearance and performance for Parasound. The HALO series represents a departure from Parasound’s traditional black box styling and is clad in a silver brushed metal finish. Each component in the series has a groove, forming an accent line across the bottom portion of each unit. The end caps of each front panel are slightly off-color from the panel itself. Each of the HALO components has a red "P" at the top center that lights up when power is present. I give the front panel the utter coolness award for its faint blue light emanating from behind the buttons which forms like its namesake -- a halo effect.

The T 3 retails for $600 and is a full-featured tuner, measuring 17" inches, by four-and-one-eighth inches in height, 13" inches in depth and weighing 15 pounds. Some of its features include RDS, 60 memory presets, IR input and output jacks, wireless remote and RS-232 control. The T 3, as with the other pieces reviewed, impressively provided balanced XLR connections and 12v triggers. Looking inside the tuner, I found a host of features and a nice-looking, well-laid-out design.

The power supply of the T3 is constructed of a large toroidal transformer, housed in an epoxy-filled steel canister. The audio signal path and the switching/control circuits have independently regulated power supplies to reduce interference. The multi-gang front end and discrete multi-stage RF circuits are mounted on a dual layer glass epoxy circuit board. Murata filters are utilized in the IF bandpass circuit and laser-trimmed Burr-Brown OPA 2134 FETs are used in class A operation for nearly all gain functions. The remote control that comes with both the T 3 and P 3 are the same, allowing one remote to control both units. The remote allows for selection of one of station presets, direct access of a frequency, or merely scrolling up and down through the available stations.

The new P 3 HALO preamplifier shares many features with the T 3, including its dual layer glass epoxy circuit boards, 12 trigger jacks, balanced connections, IR relay jacks and RS-232 control. The P3 retails for $800 and is a full-featured preamplifier with a phono section, headphone output, processor loop and the above-mentioned balanced connections and remote control. The P 3 measures 17 inches in width, four and one eighth inches in height, 13 inches in depth and weighs 16 pounds even. Each of the units in the HALO series can be rack mounted using a bracket that is screwed to the chassis behind the endcaps using existing chassis screws.
The rear panel of the unit sports a pair of balanced inputs, six line level inputs, a processor loop for theater connection, a detachable AC power cord, balanced and single-ended outputs - features typically found in more expensive products. There are also several switches, allowing the user to choose input voltage, utilize one of the line level inputs as a MM phono input, and lastly a switch that lifts the ground to reduce hum on my review sample unit. Subsequent models of the P 3 will actually not have the ground lift as Parassound found it was unnecessary for a preamplifier. The P 3 has three "direct" inputs, two line level and one balanced, although only two of the three can be used at a time. The direct inputs bypass the tone controls and record output to provide a purer and cleaner signal path.

The P 3's power supply, like that in the T 3, starts with a large toroidal transformer that is encapsulated in an epoxy-filled steel canister to reduce transformer noise. The audio signal path and control circuitry power supplies are again kept separate. The input signals of the P 3 are run through the Burr-Brown devices with FET input stages as found in the T 3 tuner. The P 3 utilizes analog ICs for volume and balance controls, according to Parasound, these ICs allow for closer level matching than the traditional potentiometer.

The last piece in the HALO trio is the A 23 stereo amplifier. This $850 amplifier boasts 125 watts of THX Ultra 2 certified power per channel via John Curl designed circuitry. This unit measures very similarly to the P 3 at 17.5 inches in width, four-and-one-eighth inches in height, 13 inches in depth and again weighs 16 pounds even. While most amplifiers have little or no features to discuss, the HALO A 23 has several. The front panel shares the same aesthetics as the rest of the HALO line yet at the center of the accent groove are two status lights. These lights glow blue during normal operation and red if a fault is detected. There is a small light to the right of the panel, which lights up red if either channel overheats.

The rear panel of the A 23 has both single-ended and balanced inputs, single-ended loop outputs, detachable power cord, handles for easier handling of the amplifier and 12v trigger jacks. There are also switches to lift the ground, an automatic turn-on mode, mono/stereo and switches to choose between balanced and single-ended inputs. Lastly, there are independent gain controls for each channel.

The A23’s power supply begins with a 1kVA encapsulated toroidal transformer with independent secondary windings for each channel. This John Curl design has a hybrid circuit topology for the A 23, utilizing JFETs, MOSFETs and bipolar transistor. Each stage of amplification is complementary, meaning half the transistors amplify the positive half of the musical waveform and half the negative side of the waveform. Differentially arranged JFETs are used for the input stage, taking advantage of their high impedance. MOSFETs are used in the driver stage, as they are known for generating less odd-order harmonic distortion than bipolar transistors. The output stage utilizes three pairs of bipolar transistors per channel. Bipolar transistors are better suited than MOSFETs for delivering large amounts of voltage and current, as they have a much larger safe operating area. The A 23 has several protection devices, DC offset is maintained by a servo system that operates outside of the audio signal path, current sensing transistors and relays are also utilized in the A 23’s protections scheme.


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