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  • QSC PLD 4.5 Digital Processing Power Amplifier

    By Craig Vecchione |

    Four 1,250-Watt Channels with DSP Processing, but only 22 Pounds?


    Many of us use powered speakers, but there are a huge number of passive boxes in use, and we need to power them with something. We all like to get more from less, right? Why not have four channels of amplification in a 2RU space? While we’re at it, let’s throw in all the speaker processing needed to drive those amps correctly and safely. And let’s keep it light and small…our backs aren’t getting any younger. QSC has answered this call in a big way with the PLD Series power amplifiers. With maximum 4-channel power ratings ranging from 400 watts continuous (PLD4.2) to 1,250 watts (PLD4.5) these amps can handle most any power requirement we’re likely to encounter. Let’s have a closer look at the PLD 4.5:



    What You Need to Know


    • Four amplifier channels feature Flexible Amplifier Summing Technology™ (FAST). FAST allows the total available amplifier power to be distributed across one, two, three or four channels. No need to bridge channels, or waste an unused channel.


    • Four channels of DSP speaker processing: crossover, parametric EQ, limiter and alignment delay are available on each channel.


    • 50 user presets and 20 factory presets that can be modified. Different venue and rig settings can be saved and recalled as needed.


    • Preset Wizard with a selection of settings for commonly used passive speakers.


    • Universal switchmode power supply with power factor correction allows light weight and can be used with any available power supply from 120-240 volts, 50 or 60 Hz. The IEC power inlet socket is locking, reducing the danger of unexpectedly unplugging the unit mid-show. The power supply is from the fairly legendary PowerLight series amps. That’s nice lineage, to say the least.


    • 2RU (3-1/2”) height and 16 inch depth, weight 22 pounds.


    • An LCD display and series of controls allow navigation through the processing menus and displays system status, available voltage, current draw, and amplifier processing configurations. I found these to be fairly intuitive, but navigation speed was limited by the simplified button/knob arrangement.


    • In four channel mode, power output is 1150 watts (continuous) into 8 ohms, 1250 watts into 4 ohms, and 625 watts into 2 ohms. Yes, power is reduced into 2 ohms due the current limiting protection, which will reduce or eliminate the overheat problems often encountered when running low impedance speaker loads


    • In 1 channel mode, power into both 8 and 4 ohm loads is 4200 watts, 4250 into 2 ohms, and there’s even a 1 ohm rating of 3700 watts.


    • Typical distortion is 0.01 – 0.03% at 8 ohms, and 0.03 – 0.06% at 4 ohms, with maximum distortion of 1%.


    • Gain at the 1.2v setting is 38/4dB


    • Damping factor is >150


    • Maximum input level at 1.2v setting is 3.88v (+14dBu) and at 3.9v setting is 12.28v (+24dBu)


    • The four XLR input channels can be soft patched to the 6 NL4 outputs to run one channel of amp/output each, or paired up with any combination of amp/output, with or without crossover, limiting, delay, and/or EQ. The ability to use any number of channels and make full use of available amplifier power is pretty neat, and makes the PLD a good choice for users who need the versatility of changing speaker configurations to meet various show requirements. No more swapping amps out of racks or hauling unused amps to that small show.




    • The user interface is somewhat hampered by the control knob programming which changes velocity proportional to the speed it’s turned. So a short quick turn does as much as a long slow turn, but it’s hard to judge how far and fast to turn the knob for a given desired change. The result is feeling somewhat disconnected from the control.


    • A copy feature would be nice to have in order to speed up the creation of multiple channels with identical settings, as would be used for monitor mixes, etc.


    • I would be remiss if I didn’t mention that it took three tries to get a working sample of this amplifier from QSC. The first two suffered the same problem; both had an “amp boot failure” message upon startup. The first unit was a pre-production prototype that had obviously been around the block a few times, and the second was a production unit.




    My experience with QSC has been that they have very good products and excellent service, so the failures were surprising. As a result of this, the sample unit has been in my possession for several months and many hours have been put on it. Basically I’ve pounded it as hard as possible without abusing it. It hasn’t skipped a beat at all, powering 2 ohm subwoofer loads for hours in hot conditions while also powering the mid-highs. I’m certain the demons possessing the early models have been vanquished.


    The uses for this type of amp are many. Obviously one PLD 4.5 can easily power a complete club system with two subs and two mid-highs. Another unit would also run the typical four monitor mixes found in many systems. With four channels and complete speaker processing, a club system could consist of two PLD amps in a 4U rack. And of course for the minimalist, one channel on mid-highs, another on subs, and the other two for monitors would make a great bar band rig. Considering what four channels of driverack would cost, plus the cost of four 1200 watt amps, the price is very competitive.





    Musician’s Friend QSC PLD 4.5 Product Detail Page - MSRP $2,933.33 Street $2,399.99


    QSC PLD Amplifier Page


    QSC Home Page





    Craig Vecchione is an IT professional by day, and dabbles in pro audio and bass guitar in his spare time. He’s been the moderator of the Live Sound Forum since 2006.



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