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Author Topic: QSC PLD4.5 four-channel amplifier  (Read 382 times)

Jonathan Woytek

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QSC PLD4.5 four-channel amplifier
« on: September 22, 2017, 03:04:27 pm »

Hi all. What follows is an initial review after a couple of uses of the QSC PLD4.5 four-channel, 5000W (at 4Ω) amplifier.

I am a single-person owner/operator-style sound provider, rebuilding a PA rig after several years away from the work. I have been using systems provided in the couple of venues I was still working for theatre events, but those systems have gradually become more damaged/less usable, with no apparent plans for upgrades, repairs, or replacement by the venues. I was interested in doing some more of the small local festivals, and having a rig that would work for the theatre events I do, and so I started to go about putting together a new PA system.

Some of the goals for this system were:
* Components should be flexible and multi-use, when possible
* New technology should be preferred over old technology
* I will not have help at all events, so the system should be manageable by one middle-aged human who is not getting any younger
* Equipment should be evaluated with an eye to long-term reliability and longevity
* Used is OK, as long as it complies with all of the above
* I don't expect to recover costs quickly, but prices should be kept reasonable

I will have additional reviews of other components posted here in separate topics, to help people looking for specific information.

The main PA is powered by two JTR Noesis 3TX mains over two JTR Captivator 212pro subs. Two more Captivator 212pro's will be added to this rig within a year.

When looking for amplifiers, I had initially focused on amplifiers without DSP, since I was intending to have a drive DSP unit located with the amp. I was also looking at two two-channel amplifiers in fairly standard configurations, though I was looking at the newer lightweight technology.

During my evaluation, I came across the QSC PLD series, and found the features intriguing. Four channels in two rack spaces, lightweight, flexible configurations, DSP, computer control, and the cost was reasonable compared with purchasing two separate amps. The DSP became more interesting when I learned that I could set voltage-based regulators there, for really accurate protection of my new system. 

OK, enough about the decision process and background. Let's talk about the configuration and the amp in use!

First up, the on-board and computer user interfaces are both well done. The computer interface is via a USB port on the back of the amp. QSC provides the Amplifier Navigator software (Mac or Windows), which automatically finds the amp and can be used to control multiple amplifiers at once. The software is laid out well and seems stable. In addition to setup features, it provides for an off-board library of speakers and amplifier presets (in case you have more presets than memory will allow, and/or to copy presets and speaker settings amongst multiple amps), and a monitoring system that graphs system stats (temperature, voltage, amperage, impedance, etc.). The on-board user interface is operated by a few buttons and a single knob, and is likewise easy to navigate and use without a manual present, which is great. I was able to read the display in sunlight, too, which is also a helpful feature. I really wish that the amp had ethernet connectivity and the ability to modify settings and monitor the amp remotely. In the future, I may add a USB<->ethernet interface box to make this work.

The front panel includes the ability to mute individual outputs via simple buttons over each meter, and a global mute by pressing the power button once briefly (no joke--it goes into an all-mute standby state). There is a separate physical power interrupt switch on the rear of the amp, near the locking IEC power cord.

Amp channels can be configured as individual, paralleled, or bridged (to increase available voltage or available current). All output is via Neutrik NL4's. There are outputs for each individual channel, plus separate outputs for A+B and C+D if running in bridged mode. The outputs are clearly labeled with their pin-outs. If I remember correctly, they do include an option to power a bi-amped cabinet off of a single NL4 (not one of my use cases, so I didn't pay that much attention to that detail--sorry!). When channels are operated paralleled, one can use one or both of the NL4's for those two channels. In bridged mode, of course, one must use the bridged output.

All inputs are via XLR. Each input has a paralleled through to run to additional amps or other devices. The DSP provides flexible control of input to output routing, including the ability to combine inputs.

Since I would have control of my chosen system DSP from FoH (Xilica XP-4080, which provides ethernet connectivity), I decided to do only a couple of presets on the amp for the moment. First was a preset that had limiters configured, but no other processing. The other preset had limiters and crossover filters configured. Both presets had the amp configured as AB, C, D (paralleled channels for the subs, individual channels for the mains). My idea behind this was that I will use the first preset for first-time uses in the venues where I typically work, so I can decide on final crossover frequencies and any alignment delay needed for positioning compensation by using the system DSP. After I have my settings for those venues and configurations decided, I will create presets in the amp, and the system DSP will be handling room EQ, any system compression, and routing/processing to other systems.

I ran a test setup and a small outdoor festival with this amp in this configuration this past weekend. The amp performed exactly as expected, having plenty of power for the system, and power in reserve if needed. I was only running the system at the outdoor festival at about a third to a half of the available output, with the amp just loafing along, pulling around 2A@110V when things hit hard. I was really happy with this, especially since there were some power problems and I had to run FoH off of the same circuit as backline, which included powered monitors.

My future probably sees at least one more of these amps added to the inventory, to handle the additional subs and to serve as backup in case one goes down. If I go with passive monitors when I start to build out a monitor inventory, I could see another one of these added to handle monitor mixes (though perhaps one of the smaller models, like the 4.3 or 4.2). The fact that I could have my entire system powered in 6U is crazy by itself, then figure that there's a decent chance that it could live on a single 20A circuit for many shows, and I can move that box by myself (or easily have it split up in smaller rack cases if desired), and that's some great stuff.

I fully intend to add more details here after this gets used for a few theatre shows and at closer to max output for the system. In the meantime, if you have any questions, please feel free to shoot them my way here or in a PM!

Photo (and before you say anything, that thing at the top is a glorified power strip--it doesn't actually do anything else):

Jonathan Woytek
Dryrose Productions
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