JL Audio 500/1
www.jlaudio.com

JL Audio’s sub amp offers an adaptive and tightly regulated output.

The 500/1 is a single-channel, class D subwoofer amplifier with a power rating of 500 watts into any load between 1.5 ohms and 4 ohms. Features include the Regulated Intelligent Power Supply, which is responsible for the single power rating, differential inputs, buffered preamp outs, internal crossovers with variable cutoff frequencies and selectable slopes, a parametric bass boost circuit with wired remote, and a variable infrasonic filter.

Performance
The 500/1 is the first class D unit that we’ve seen from JL Audio and, like the rest of their amplifier lineup, this unit can vary its output voltage potential to match the load being driven, thereby producing essentially the same output power into a wide range of loads. In the class A/B amps, this is accomplished by reducing the amp’s rail voltage when driving lower impedances. In the class D amps, the duty cycle of the high frequency carrier signal is reduced when driving lower impedances, which produces the same effect.

The sidebar with the specs pretty much speaks for itself. The 500/1’s adaptive and tightly regulated output appears to work quite well, providing about 600 watts into resistive loads under a wide range of test conditions. The amp also seems more than happy driving reactive loads and posted an impressive 733 watts into 2 ohms.

The only performance shortcoming appears to be efficiency. At 1/3 of its maximum output, the 500/1 measured 57 percent efficient, which is somewhat lower than the rest of the class D units that we’ve seen to date. In addition, the efficiency remains in the mid 50’s all the way to full output rather than increasing to the 80-percent-plus that we’ve seen in other units. The result is an amp with efficiency that’s about 30 percent better than a class A/B unit at 1/3 output and roughly equal at full output. Efficiency is the main advantage to class D amplification, but this amp is likely small enough to get away with compromising a bit.

Connections & Adjustments
All connections to the 500/1 are nickel-plated and include chassis-mounted RCA’s for input and preamp outputs, and captive terminal blocks for all power (4-gauge) and speaker (8-gauge) connections. Adjustments to the 500/1 include variable input sensitivity with high/low range selector, input signal sensing enable, infrasonic filter enable and variable cutoff frequency (15 Hz-60 Hz), crossover, and bass boost adjustments. There are two onboard crossover sections, one for the amp and one for the preamp outs. Both have variable cutoff frequency (40 Hz-200 Hz) and switchable roll off slope (12 dB- or 24 dB-per-octave). Both crossovers can be completely disabled and the preout unit can be configured for either high pass or low pass operation. The preouts can also take their signal from the amp’s low pass filter when daisy chaining multiple amps. The bass boost circuit provides parametric operation with variable adjustments for center frequency (20 Hz-80 Hz), filter bandwidth (or “Q”) (0.5 to 4), and boost (0 dB-+15 dB).

Installation
When it comes to installation considerations, it’s damn hard to find anything about the 500/1 to not like. For a start, there are the chassis-mounted RCA connections. By comparison, the input connectors on most amps are unimaginably flimsy.

The preamp section of the 500/1 is also quite impressive. Much like the 300/4 that we reviewed a few issues back, its flexibility and degree of control are head and shoulders above anything else that I’ve seen in an automotive amplifier. Among my favorite features are the detented frequency controls found on the crossovers, bass boost, and infrasonic filter. Rather than continuously variable pots, these controls utilize stepped adjustments and the owner’s manual lists the exact frequency at each click. The parametric bass boost is another very cool gadget. The center frequency adjustment covers a wide and sensible range of 20 Hz to 80 Hz, the bandwidth adjustment (Q) ranges from very narrow to ridiculously wide and the circuit can be completely bypassed if you so desire. Equally impressive (in a test-bench-geek kinda way), is that the circuit doesn’t effect the amp’s response at all if the boost knob is dialed to 0 dB. All of the amp’s filters are similarly well behaved. The infrasonic filter covers a far wider range than typical, so wide in fact, that it overlaps the lower half of the crossover’s range. It’s possible to nearly eliminate all output from the amp by misusing these controls. How’s that for flexibility?

On top of all that, you get a pair of buffered RCA outputs with an independent crossover with the same cool controls, a heat sink that’s more than just a heat storage device, and an amp that won’t quit no matter how heartlessly you drive it. The amp’s protection circuits cause it to reduce output rather than shut down completely. What else could you ask? Well...I’d really dig a cut/boost control on the parametric, but beyond that, I’m really drawing a blank.