When I first heard that QSC was going to offer a “low cost” audio power amplifier, my first instinct was how much lower from the RMX models could they go? Then they mentioned that they will adopt the new PLX2 cosmetics and limit the recommended load impedance to 4-ohms and up, and a “great idea” light bulb lit up in my head. And when QSC management said the amplifier would suit MI users and “oldsters” like me, I knew something good was afoot.
This result was the introduction of the GX3 and GX5 audio power amplifiers with $399 and $499 manufacturers suggested list prices. The GX3 is a Class AB amplifier with a stereo 4-ohm power rating at 425 watts, and the GX5 is a Class H amplifier with a stereo 4-ohm rating at 700 watts. The GX3 and GX5 numerics have some meaning in that the GX3 delivers 300 watts per channel into 8-ohm loads, and the GX5 delivers 500 watts into 8-ohm loads. What is great about these amplifiers is that they are not skimping watts needed to drive MI speakers to full excursion, like many competitive amplifiers.
The Gear
The QSC GX series of amplifiers shares the same front and rear panel features. On the front panel, your basic power on/off rocker switch is followed by two detented gain controls for individual channel level adjustment. Each channel gets two LEDs for signal present (green) and clip threshold (red), beside a common AC power on LED (blue). What is different about the GX series from all other QSC amplifiers is that the split grille intakes cooling air from the left side and partially exhausts heated air on the right side. Some remaining heated air does exit a smaller grille on the rear panel.
The rear panel is a thing of beauty from a techno-geek perspective. On the left side, the input signals have a triple redundant choice of inputs with XLR jacks, balanced or unbalanced TRS phone jacks and unbalanced RCA phono jacks for the DJ gear interconnects. Accompanying the jacks is a crossover switch to choose from normal-full range operation to a 100-Hz crossover split with channel 1 getting the subwoofer signals and channel 2 getting the top-box signals.
Also on the rear panel, combo Neutrik NL2/Phone Jacks plus binding post handle the speaker cable interconnect tasks. With the Phone Jack feature using center orifice of the NL2, means that QSC is acknowledging our bad history of using guitar plugs and small gauge speaker wire for MI speakers. Rounding out the rear panel features, an IEC power jack and resettable circuit breaker handle the AC power chores.
Other than the previously mentioned power ratings, the GX5 provided to me for this review has pretty standard specifications with less than 0.1 percent distortion ratings at 4-ohms, and a frequency response of 20 Hz to 20 kHz at the +0, -1 dB points. Damping factor is a barely adequate 100, but that is an okay trade-off for a cost sensitive amplifier circuit. And the six ampere draw at stereo 4-ohm loading to 1/8th power shows club power friendliness of the Class H amplifiers. Of course, the conventional transformer-based power supply does impact the chassis weight of 26 pounds.
My curiosity got the best of me, due to what makes the GX5 a low-cost power amplifier offering with the QSC branding. After popping off the lid, and noting the “Made in China” labeling on the rear panel, I saw the reality of the technology. By designing the amplifier for only 4-ohm or higher speaker loads, the heatsinks could be reduced considerably along with the power transistor count. And the well-executed ducted fan cooling into the heatsinks puts the reliability concerns to rest, even with the expected torture from inexperienced sound system users.
Another aspect came from the well thought-out owner’s manual, in that the 2-ohm rating is 350 watts per channel; assuming you ignored the rules and wired up four 8-ohm loads per channel. So, instead of getting the 700 watts per channel at 4 ohms, or 350 watts per 8-ohm speaker, the 350 watts per channel at 2 ohms places only 81 watts per 8-ohm speaker; an audible reminder that things get wimpy on loudness when you disobey the rules.
The Gigs
I took the QSC GX5 out to a couple of gigs and placed the amplifier in both the top-box application and the stage monitor application. The 700-watt rating at 4 ohms makes a nice top-box amplifier for your typical dual 12-inch plus horn, or dual 15-inch plus horn full range speakers for club applications. In this situation, the GX5 kept cool all gig long and had enough snort for a rock ‘n’ roll club gig. The next test was handling a pair of wedges per side, in a similar rock ‘n’ roll/screaming vocalist kind of gig. Again the GX5 handled the chores of making the wedges scream back at the vocalists without running out of headroom or thermaling out.
Many shop tests were equally torturous and the GX5 passed with flying colors. While the design of the GX5 does not compare with RMX and PLX design in terms of extra heatsink and parts, I could not find anything wrong with its performance or design. And I think the GX amplifiers deserve good marks in delivering on the low-cost attribute without suffering on the cheese factor many other MI market competing models show.
What it is: QSC GX5 Power Amplifier
Pros: Compact and rugged, enough power, price point.
Cons: Nada for the price.
How much: QSC GX5 $499 MSRP
Web site: www.qscaudio.com.
