Audison LRX 6.9 - Test Amplifier

Measurements: Redrock ElectronicsYou've got to love Italy. Great food, great wine, fast cars, mafia and mobile electronics. But just how seriously do Italians take their tunes? Audison, part of the Italian Elettromedia group, has been at it a long time. In this issue we take a look at the latest from the country known as "il Belpaese."

The Audison LRx 6.9 is a 6-channel, regulated Class A/B amplifier with rated 4-ohm power of 70 watts x 4 + 75 watts x 2. Each channel pair (A, B and C) has its own set of crossovers specific to its most likely use: Channel A has fullrange or highpass from 50Hz to 5kHz at 12dB/octave; Channel B goes a step further with fullrange or highpass between 50Hz to 1kHz and lowpass from 250Hz to 5kHz. The highpass and lowpass can be used together to create a bandpass - just make sure the lowpass crossover point is set higher than the highpass point. Channel C, obviously intended for subwoofers, has a lowpass from 50Hz to 1kHz at 12dB/octave or 24dB/octave, plus a subsonic filter selectable between 20Hz or 30Hz at 24dB/octave.

One of the most unique features of this amplifier is the signal input connector, termed ECI for Easy Common Interface. When an amplifier is capable of using both RCAs and speaker level inputs, you will usually see both sets of connectors on the endplate. The Audison engineers have come up with a way to have both (plus RCA outputs) without requiring additional endplate real estate. There are two ECIs that come with the amp - one is for RCA inputs and pre-outs; the other, for speaker level inputs and RCA pre-outs. The ECI modules plug into a multi-pin header in the end shroud, sending the signals to the appropriate pins on the circuit board. As an added benefit, the modules are symmetrical so that you can plug them in with the connections facing out, or with the connections facing in, which leaves a smooth surface on the outside of the amp. There are cable routing channels in the bottom of the amplifier for your RCA or speaker cables, resulting in a totally clean installation. Audison even went as far as to include a template for you to cut wiring holes in the amp mounting board exactly underneath the connector locations. The labels for the connections are printed on the amplifier itself, so connections are easy whichever module you use, and whichever way you turn them.

With rounded corners, strips of closely spaced heatsink fins on the main extrusion and rounded cast endcaps, this amplifier looks like a low-profile version of a bullet train. The main extrusion sports a textured metallic blue powdercoat, while parts of the endcaps and the full-length, backlit logo strip are textured silver. A black sheet-metal bottom plate keeps the insides clean.

Under one endcap you find the power and speaker connections, all using metric socket head screws into substantial metal slugs for terminal blocks. There are also terminals for remote on, remote out, speaker on and subwoofer volume. These terminals require that you assemble a crimp terminal and plastic housing to your wiring before you can make the connection. On the plus side, Audison supplies a handy 4-way tool with both required Allen drivers and two screwdrivers for all the connections and adjustments you'll need to make.

The opposite endcap is longer and houses the input connections (the aforementioned ECI modules) and all of the controls, which lie directly under the top cover. Audison supplies eight overlays for the control section, which correspond to eight different speaker configurations you can set the amplifier for. When you put the overlays on top of the control section, unused functions are crossed out and switch settings are specified right on the controls to help you make your settings very quickly. A very nice touch.

CircuitryI don't think I've ever seen as many daughter boards in an amplifier as there are in this one. The main pcb runs the length of the extrusion, actually protruding about an inch on the end with the power connectors. On the input end is a 4"-long daughter board that joins the main pcb by way of two multi-pin connectors. It's a big daughter board, but the cool thing is that the entire input section - crossovers, gain controls, input connections - is on this board. Besides the advantages of a totally modular setup, this format also isolates the low-level circuitry very effectively from the noisy power supply.

Each side of the main board is lined with additional vertical daughter boards. There are six amplifier stage modules (one for each output channel), six output device module boards, two power supply switcher/rectifier modules and two power supply control modules in the middle of the main board.

The power supply is perfectly symmetrical, occupying approximately one third of the main board nearest the power terminals. There is an 80-amp fuse bolted directly to the top of the B+ terminal, which transfers the juice to a heavy-gauge inductor. Four 1,500F capacitors filter the incoming current on the primary side of the transformer. Speaking of the transformer, this one starts out as a basic 2" Litz-wound toroid, but it's a little different. Usually the "legs" of the transformer connect to the circuit board pretty close to the transformer. The winds of this one are extended by about an inch and a half so that they contact the circuit board very close to the source (B+ and ground) on the primary side. This lowers the resistance into the transformer, allowing higher current flow. The transformer is "switched" by three pairs of transistors rated at 190 watts dissipation each. The switchers, in turn, are controlled by a surface mount TL494 PWM chip at a frequency of 39.6kHz. The PWM control circuitry is all contained on one of the vertical daughter boards, back to back with another daughter board holding a 16-bit programmable IC that presumably processes all of the protection circuit information and possibly enhances the regulating abilities of the TL494. I suggest that function based on my observations that this is the most precisely regulated amplifier I have tested.

The transformer feeds a set of high-current rectifiers that convert the AC voltage back to + and -26.7VDC rails for the output devices. A dual-toroid core inductor and a total of 12,000F worth of secondary capacitors stabilize the rails.

Jumping to the input end, incoming music signal is processed on the daughter board and fed to the vertical amplifier stage modules placed symmetrically down each side of the main board. Each stage module drives the output daughter boards on the very edge of the main board, allowing the output devices to be clamped to a horizontal step of the heatsink extrusion. The output modules also contain individual thermal sensors and good, old-fashioned bias controls for fine-tuning each channel. There is a single pair of 80-watt output devices for each of the first four channels, while channels five and six have two pairs per channel. Operating on the same rails as channels one to four, this is how channels five and six can put out more wattage at the same impedance, but more importantly, how they can be dropped to 1 ohm for almost double the output.

PerformanceThe LRx 6.9 performed very well on the bench. All of the crossover measurements were so close to the stated performance that the difference didn't matter and the frequency response was 3Hz to over 45kHz. While the power output was a tad low at 14.4 volts of input (maybe 4 percent or so), it was identical at 12.5 volts. The regulation of the power supply is designed to deliver the same output at lower voltages as it does at 14.4 volts, but I've never seen one do it better than this. My power measurements were EXACTLY the same at 14.4 volts as they were at 12.5 volts. I checked the readings several times and played around with the input voltage. In fact, the output power remained consistent down to about 11 volts of DC input - pretty amazing.

Thermal, short circuit and reverse-voltage protection circuits all worked very well, in fact quite intelligently. In most cases, the warning lights will come on to let you know something is up before the amplifier actually shuts down to prevent burning up. No turn-on or turn-off noises were present, and no audible noise when the amplifier is on.

ManualThe manual is more than adequate: 72 pages in all, though 36 of them are in Italian. It is long-winded and occasionally humorous, apparently having been translated by an Italian into the 36 pages of English information. In spite of that, there is a lot of good information, and everything is clearly illustrated and explained. If you are impatient, you'll probably read the manual when you get stuck (like I do).

ListeningI connected the Audison to my system with the A channels running the front separates, B channels on the rear 6 x 9s and C channels bridged to a single DVC 12" sub in a sealed box. I ran the front RCA to Channels A and B, and subwoofer output to Channel C for the subs. At least I thought I did.

I put in the usual Donald Fagen Kamakiriad to start my listening, only to discover that I plugged in the RCAs in reverse. After correcting the error, the whole system sounded much better. Go figure.

Back in the driver's seat, I went to track 4, "Snowbound," and heard the well-defined crunch of the low Fender Rhodes notes and very bass-sounding bass lines. I noticed that the highs of the cymbals seemed a little overbearing on this track, as well as on "Tomorrow's Girls."

I pulled out an old IASCA CD and played Jennifer Warnes' "Bird on a Wire" next. Warnes' voice was smooth and clear, and the highs seemed to be settling down a bit. Ever found an old CD and rediscovered all the great tracks? All you past IASCA folks, remember "Planet Krypton?" Played by the Cincinnati Pops, with a pipe organ, this track is unbelievable. It starts with some horns straight from a sci-fi theme, and builds as it goes. The fun part is the pipe organ bass notes that come in towards the end, descending down to the 16 to 20Hz region, when everything in the car is shaking but you don't really hear much bass. I ran this track three or four times, and way too loud. I took a break from listening, both for my ears and to let the amp cool off a little bit.

When I returned to listening, I played another old favorite - Flim and the BB's "Tricycle" - that is mainly a piano tune, but has a great upright bass and drum kit. It all sounded very good. Mary Chapin Carpenter's voice came through rich and clear on "Only a Dream" and I could hear individual guitar strings and a very present cello in "I am a Town."

After all the exercise the amplifier was getting, I went back to the original Donald Fagen tracks to find that the harshness in the high frequencies was gone. No, it wasn't because I blew out my tweeters. I have experienced this "burning in" with a few different Class A/B amplifiers in the past, but it has been awhile. The parameters of the output stages shift slightly during the first period of hard playing, as do the bias circuit parameters. It's nothing to be concerned about, and I was actually relieved that the sound quality came back into line. This is a great-sounding amplifier!

ConclusionI really like this amplifier. It has plenty of power to run the fullrange speakers to the limits before clipping and some very well-controlled subwoofer power. I found the sound quality to be in the upper echelon of Class A/B amplifiers, with precise and useful crossovers on all channels. It's not loaded with tricks, though the ECI is a very elegant solution to multiple input configurations. The max power is 913 watts, which, divided into the retail price of $999, gives you $1.09 per retail watt. That's above average for the power level, but the performance is worth it. This would be a great amp for a couple sets of nice fullrange speakers (say $200 per set or more) and a pair of 10" or 12" subs in the back. Throw in your preferred sound-deadening material and do as the Romans do.

Test Results