Audison LRx6sr Class AB Amplifier

More and more these days I see the glow of a video monitor lighting up the interior of the next car. Maybe it's an Astro van with a PS2 for the kids, or a luxury SUV stocked with favorite DVDs. The video is great, yes, but what about the sound?

With five channels at 55W (4-ohm) and a 150/220W subwoofer channel, Audison has a solution for those demanding more from their mobile theater system.

The Audison LRx6SR is a regulated class AB six-channel amplifier designed specifically for 5.1 surround applications. Front, rear and center channels are rated at 55W at 4 ohms and 80W at 2 ohms. The subwoofer channel (actually two channels internally bridged) is rated at 150W at 4 ohms and 220W at 2 ohms. Front, rear and center channels use 12dB/octave high-pass filters ranging from 20Hz to 150Hz (front and rear) and 40Hz to 900Hz (center). The subwoofer channel uses a 24dB/octave low-pass filter variable from 40Hz-150Hz, as well as a 24dB/octave subsonic filter that can be programmed for 16Hz, 20Hz (factory setting), 24Hz, 28Hz or 32Hz. The subsonic filter can be switched off if you prefer.

Connections are made by way of 3awg screw-type terminal blocks for B+ and ground, 9awg for the speaker outputs, and mini-spade terminals for the remote turn-on lead and the optional subwoofer remote volume control. The amplifier makes use of overload and thermal protection circuits with indicator lights on the control panel to tell you what's going on.

Cosmetics
When I saw the amplifier with its rounded cast end panels and long profile my first thoughts were of a Japanese bullet train. The blue-gray heat sink and silver ends are treated with the same rough texture, resulting in a good match. According to the manufacturer, the texture is the result of aluminum particles mixed into the powder coat to enhance thermal dissipation. The crossover and gain controls are on the top of the amplifier along the silver logo strip, which can be reversed according to your mounting orientation. I must note that it would be nicer if the gain controls for each section corresponded with the crossover control right next to it. All of the connection terminals are inside the outline of the cast ends, contributing to the very finished impression. Audison has custom-tooled a fuse receptacle complete with a hinged window, and it has included a handy four-way tool that you'll use for everything except the mounting screws.

Circuit Design
The internal circuitry is laid out in orderly and logical fashion, reflecting the location of the respective external connections. The power supply is at one end with long vertical daughter boards moving the rails to the output devices. The output sections are along the sides, as are the speaker connectors, and the signal path and crossover sections extend into the middle of the board, reflecting the input connector locations and top controls.

The double-sided, printed circuit board is predominantly surface-mount, with all components within the various sections neatly lined up like so many tiny neighborhoods. A great deal of attention has been paid to orientation of polarized components during the circuit layout. This makes the amp easier to troubleshoot during prototype and repair, and saves a few split seconds during parts placement in production.

Power Supply
Audison went with a regulated supply built around the surface mount SG2525a controller, switching at about 30kHz. From the connection terminals the B+ goes immediately through a proprietary fuse holder and 5-turn inductor into the transformer primary, all within two inches of the power terminals. With four 1500uF, 105-degree C caps and the inductors, very little noise will get to the transformer. The toroidal transformer uses multi-strand bundles for both primary and secondary windings. The secondary windings feed the transformer output through two toroid inductors, one for the positive and one for the negative rail, each stabilized by a 5000uF capacitor. The rails are transferred to the output sections via vertical daughter boards that run two-thirds the length of the amp.

Input Section
The input uses a quasi-differential design with isolated grounds. A design like this will reduce noises radiated into your RCA cables by means of common mode rejection. The 10-ohm isolation on each ground will also eliminate the possibility of ground loops from your head unit. The signal goes directly to the gain control daughter board within two inches of the RCA connectors, and then from the gain daughter board over to the crossover daughter board next door, and on to the output section. High quality sealed potentiometers are used for all controls.

Outputs
The five 55-watt channels each use a pair of large TO247 devices capable of 200 watts total dissipation, used in a Darlington configuration. The subwoofer channel is made up of two individual channels each using a pair of 200-watt devices, again in a Darlington configuration. Output power is transferred to the output connectors by the same daughter boards that bring the rails to the output sections.

Performance

Frequency Response
Audison rates the bandwidth of the LRx6SR as 4Hz to 85kHz at -3dB points. I measured the low end of the subwoofer channel to be -1dB at 6Hz; so it corresponds to the company's measurement. The top end is a bit complicated, as our gear will only measure out to 48kHz. The Audison was -0.23dB at 48kHz. I expected to see some artifacts around the power supply switching frequency of 30kHz, but there were none.

Overall, I was very impressed by the test results for this amplifier. It makes more power at lower distortion than Audison promises it will. The only inconsistency was in the crossovers, all of which were at lower frequencies than they were supposed to be.

Crossovers
All of the crossovers have very clean slopes and roll off without any bumps or knees indicating component misalignment. The 12dB front/rear high pass ranged from 21Hz to 156Hz (20Hz to 150Hz rating). The center channel 12dB high pass was at 37Hz on the low side to 850Hz on the high side (rated 40Hz to 900Hz). The subwoofer 24dB low pass measured 39Hz to 144Hz (rated 40Hz to 150Hz). The 24dB subsonic, factory set at 20Hz, actually measured 18Hz. The optional VCR01K remote volume control performed as stated, although the addition of the VCA card and the remote control added 6dB to the subwoofer level. Hence the +6dB, -100dB measurement.

Protection
Both thermal and short-circuit protection work consistently, showing a red LED on the top control panel when the protection is triggered. Manually shutting the amplifier off for a few seconds and then back on will reset the circuits. There were no audible turn-on or turn-off noises.

Owner's Manual
The owner's manual has been "translated" from the Italian, but perhaps not by a stereo enthusiast. It's actually more amusing than irritating, but it certainly could have been done better than this. While the manual doesn't walk you through the usual precautions about drilling through fuel lines and disconnecting the battery before you start, it does tell you everything you need to know about this amplifier and its accessories, including a block diagram of the signal flow. Other than the odd phrasing, the book is very thorough, with plenty of clear illustrations and instructions.

There was no warranty information in the box in which the amplifier came, but a quick call to Audison's U.S. distributor revealed that the amp is covered for one year if bought over-the-counter, and three years if installed by an authorized Audison dealer.

Listening Test
The LRx6SR was installed in a '99 Regal LSE, driving four 6.5" coaxes and an SVC 4-ohm 12" subwoofer in a sealed box. Unfortunately there is no provision for a center channel speaker in the car, but it would get a workout in the listening room later.

There was no turn-on or turn-off noise; in fact, no noise at all to reveal whether the amplifier was on or off. With the engine running, lights and AC turned on, there was still not a whisper of noise. Back in the listening room the Audison was connected to a Sony SACD/DVD player. The surround speakers consisted of one pair of Clements Audio 8" two-ways for the front channels, one 5" two-way for the center, one pair of 6" two-way rear speakers, and the 12" subwoofer brought in from the car. Relative levels were set from the DVD menu test tones, and listening began. Again there was no turn-on or turn-off noise, and even in such a controlled environment there was not even a whisper to tell you the amp was on.

First up was Steely Dan's Two Against Nature. All of the tracks were impressive with tight bass and kick drums, very present vocals and superb cymbals to polish things off. Of special interest were the female harmony vocals, which were reproduced flawlessly. Music seemed to work fine, so I put in The Matrix and went straight to the lobby shoot-em-up scene. From the tinkling of shells on the marble floor to the rich bass line, everything was clear and loud. The drums in the kung-fu fight scene were especially rich. I was able to drive the system very hard before any graininess occurred -- a much higher volume than most people would listen to.

Conclusion
This amplifier exhibits superb sound quality throughout the audio range, with well-controlled bass and clear mids and highs. Both the power supply and output sections are somewhat overbuilt, so it behaves predictably under stress. The differential-type input section keeps the signal path very true, and all the nice cosmetic details add up to a very satisfying amplifier indeed. All of these things come at a price, however, and at $950 retail the amp's value works out to about $1.31 per watt at maximum output. Though you could certainly make more noise for less money, I consider this amplifier to be ideal for mobile surround applications where sound quality, style and reliability are paramount issues.