A year ago, QSC debuted its PLD (for portable/live sound applications) and CXD Series (contracting/installed sound) amplifiers. Available in several power configurations, all are 2-rackspace, Class-D multi-channel amps with slight feature set variations catering to their intended use, but sharing a radical new channel-combining methodology, with flexible onboard signal processing as well.
The FAST Approach
Known as FAST (Flexible Amplifier Summing Technology™), this new technology platform offers improved power allocation by distributing the amplifier’s total power output across one, two, three or all four outputs. Any combination of channels can be assigned (bridged) to a parallel output for more power, at loads as low as 1 ohm.
Meanwhile, the high impedance performance has also been extended via a bridge/parallel combination. With a 4-channel amplifier, two pairs of channels can be independently paralleled, and the parallel combination is then bridged, providing double the voltage and current, with full amplifier power deliverable into an 8-ohm load. This FAST platform came about through QSC’s development of a proprietary high-power/high-current MOSFET output device, matched with a pair of high speed, low loss current steering diodes. QSC also developed a method of controlling the switching action within the individual Class-D modules to within 60 nanoseconds of each other. This timing synchronicity enables identical switching within the power modules, so the same amount of current is delivered to the load by each channel.
Depending on the model, 1,600, 2,500, or 5,000 watts of total power can be distributed across one to four outputs. On the mid-line 2,500-watt PLD4.3 we tested (625W @ 8 ohms continuous from a 21-pound package), setting up a 1,250W to drive a sub, with two 625W top cabinets was no sweat and the same applied to assigning all 2,500 watts to a single output.
Borrowing on its successful past products, PLD amplifiers use QSC’s proven PowerLight power supply and Power Factor Correction to align the current waveform with the AC mains voltage waveform. PFC lets the amplifier draw current from the wall in a more efficient, controlled manner resulting in very high power from a single standard AC breaker.
Efficiency, Defined
All of the PLD (and CXD) models have four channels and share a common 2U chassis. The PLD rear panels have four female XLR inputs (with four male XLR thru/parallel jacks), four Neutrik NL4 outputs to speakers and two dedicated NL4 outputs for bridging applications, along with power switch, fan inlet, locking IEC AC power connector and a USB port for connecting to a computer running the free (Mac/PC) Amplifier Navigator software. (The cousin CXD contracting models substitute features such as Euroblock I/O connectors, 70/100 volt direct drive, input mixing on each channel and are compliant for life-safety installs.) The front panel has airflow outlets, individual mute buttons for each amp channel, a 400 x 240 TFT informational screen, navigation buttons, channel meters/indicators and a secondary power switch. As long as the rear switch is on, this secondary front switch can select run, standby or mute-all modes. The rack handles are cramped and awkwardly designed — it’s no issue once the amp is in a case, but these need to be changed in the next run.
Speaking of cooling, the PLD ventilation is very efficient. In fact, even when pushing the amp hard (driving two 4-ohm bass bins bridged into a 2-ohm load), the amp remained fairly cool and fan never kicked into high speed. I do think that the amp could use a simple foam filter over the inlet, just for dust protection. However, the PLD uses a unique construction whereby the main circuit board hangs upside down within the chassis, so any dirt, or moisture encountered would settle amp’s bottom plate, rather than onto the PCB. It’s a simple idea, but smart.
A nice touch is a display of the operating temperature of the MOSFETs and power supply on the TFT screen, along with readouts of the line voltage and AC current draw. And if you plan to travel, the amps’ universal power supplies operate from 100 to 240 VAC, 50 or 60 Hz. Another useful feature is energy-saving, multi-stage sleep modes that minimize power consumption.
DSP to Go
Far beyond a card or simple plug-in module, the PLD’s onboard processing is deep and versatile, while integration of the DSP into the amplifier itself lets actions such as peak and RMS limiting to operate seamlessly and effectively. The DSP includes four channels of crossover filters (at 6 to 48 dB/octave slopes, with a choice of Butterworth, Linkwitz-Riley,or Bessel-Thomson variants), 5-band parametric EQ, alignment delay and more, including Intrinsic Correction™ for QSC arrays. A library of tuning profiles for more than 60 speaker systems from various manufacturers is included.
Management is via front panel controls. I will admit that I’m not much of a fan of the programming via small front panel screens, but in this case, QSC did it right. Navigation is fairly straightforward and I never felt lost or left wondering what to do. When I wanted to set up that bridged sub with two top cabinets, it was right there — hit button, load and go. A useful system setup wizard helps you select the right preset, or select one of the 20 configuration templates and create/save custom tunings in the user preset library.
Alternatively, you can connect a PC or Mac to the amp and use the free Amplifier Navigation software for large-screen setups or simply copying presets to/from the amp and PC. I wanted to run it on an older Mac laptop using Snow Leopard OS 10.6.8, yet nowhere on the QSC site could I find any mention of system requirements. I successfully installed the software, and found the menu telling me I could install on the computer I was running the software on. BTW, it’s 32- or 64-bit via Windows XP through Win8 Pro, and Mac Snow Leopard, Lion, Mountain Lion.
Other basic front panel functions — such as setting gain (-100 to +20 dB) or input sensitivity (+4/+14 dBu) were a snap and I appreciated the front panel output mute buttons for each channel. Every once in a while, there’s a immediate need to “mute everything” and it’s nice that function isn’t buried in a menu somewhere. Thanks!
The Wrap
Over a period of time, on a variety of systems — ranging from simple biamped monitors including QSC’s very nice, low-profile Acoustic Performance AP-5122m 12-inch two-ways) to tight and nicely damped LF from subwoofer bins, whether simultaneously driving top cabs or taking the 4-into-1 2,500W bridged feed. And it never hiccupped, even into 2-ohms. So in taking that famed QSC sound and reliability and putting it into a lightweight, flexible package with ample DSP, these guys have a winner with the PLD series.
At a Glance
QSC PLD Series Amplifiers: Power and Finesse
The PLD series are lightweight, Class-D power amps with powerful onboard DSP and flexible FAST-technology channel assignability.
Manufacturer: QSC
PROS
Great sound, versatile DSP, solid construction, easy programming, flexible channel assignments.
CONS
Awkward rack handles, could use a fan filter.
Street Price: PLD4.2, $1,399; PLD4.3, $1899; PLD4.5, $2,399.
More Info: www.qsc.com
