ProtectionTo be honest, we did not try to drive the amplifier into thermal protection. While we have massive loads and supplies here, they aren't that massive. I'm certain you won't be able to even warm up this amp either, but if you do there is a good possibility you will have some hearing damage (considering how much power is on tap). The only way we were able to get a rise in temperature on the amp was from drawing over 14,000 watts on our three-phase service through our power supplies - yeah, it gets a tad warm in our lab.
After some searching, we found someone brave enough to short the outputs of the 8,200 watt A6000GTi. Really, we had no reason to be afraid; it shut down the outputs perfectly with direct shorts and went into current limit protection when the load dropped below 1.5 ohms. The big JBL also shut down with (battery) voltages higher than 15.4 or lower than 9 volts. In addition, this amp has a magnetic safety interlock switch that keeps one from being electrocuted by the extraordinarily high voltage available. This is a great idea especially since the A6000GTi can develop over 220 volts on its speaker leads. While the amplifier may protect you from shock with its protective cover off, the connections to the speakers are not usually protected.
Internally fused at 600 amps, JBL recommends an external 500-ampere fuse near the batteries (yes batteries - one will not suffice), as in any quality installation. And taking the cover off to replace the internal fuse is not an easy task to perform on a mounted 88-pound amplifier, especially if it is in a small compartment.
CrossoverThe crossover has selectable slope with adjustable frequency and damping. JBL calls this DBO, or "Dynamic Bass Optimizer." (See graph, "DBO Frequency Response.") This is the first I've seen of adjustable damping. It's a neat feature, as you can purposely under-damp the crossover to get a bass boost effect right above the crossover point, theoretically, right where you'd want it. Additionally, as the boost comes just before the low frequency cut-off, this effectively acts as a steep filter to prevent unwanted output below the speaker's port resonance. This will prevent excessive cone excursion at frequencies where the cone is unloaded.
Front Panel ControlsThough understated compared to the rest of the amp's design, the front panel display and controls are clearly labeled, and allow you to tweak the unit for a precise match for your speakers, enclosures and vehicle. Blue LEDs report status and accent the connection for the remote level control, giving it a sleek clean look.
The included remote level is functional, but expect to see 3rd party panels for this amp soon. JBL kindly put extra connections on the remote level port, so it is not only a remote input, but also has status lines for voltage, current, and temperature of the amp to connect to gauges or displays.
ManualThe manual supplies plenty of technical information to hook up this amp in the best way for the equipment that you have. There are some contradictions such as the cable used for the remote (though this may have been cleared up in the final printed version).
PerformanceThis amplifier has two power output channels, but is actually a mono amplifier. It cannot be configured as two independent stereo channels since the left and right audio paths are summed in the preamp stage. These two channels can drive two 2 ohm loads independently; they can be run in parallel into a single 1 ohm load; or bridged for 8,200 watts into a single 4 ohm load. When driven into slight clipping (1 percent THD), this amp drew a whopping 760 amps! We did not drive it into hard clipping, as we were bumping into the limits of our bench supply (four 240 volt, three-phase supplies in tandem). This low-frequency amplifier delivers more that 8,000 watts at very low distortion, typically below 0.05 percent, another benefit of Class I over Class D. The A6000GTi exceeded the factory power rating by over 2,000 watts.
JBL's beast is no doubt powerful, low in distortion, with very versatile output configurations. Yet that's not all-this amp's efficient, too. Efficiency at full power into 2 ohms was a highly acceptable 76 percent! At 4 ohms per channel efficiency climbed to an astonishing 85 percent. This is the best efficiency we've measured for any amplifier under these conditions. Even the damping factor was impressive at an astounding 1015, especially for this class of amplifier.