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Author Topic: QSC PLD amps  (Read 15848 times)

Tim McCulloch

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Re: QSC PLD amps
« Reply #10 on: November 29, 2015, 02:56:01 pm »

We've used QSC amplifiers for 20+ years (w/the occasional Crest and Crown).  Two issues in 20+ years with QSC... and support was great. 

We'll stick with QSC, but I'm a little nervous with our PLD 4.2 amps as well.  Mostly because these amplifiers are computers.  And I'm well aware of how computers are (they have become nothing more than commodities).  I trust QSC... what I don't trust is the computers.  This is why I will never go digital for a console (another story for another time). 

Don't recall where I read/heard this... class D amplifiers don't do too well for bass frequencies.

That's patently false.  Lab Gruppen, Crown I Tech and many other Class D amps have no problems on sub woofer duty.  It's not the class of output, it's the robustness of the design.
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Bob Faulkner

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Re: QSC PLD amps
« Reply #11 on: November 29, 2015, 03:26:37 pm »

That's patently false.  Lab Gruppen, Crown I Tech and many other Class D amps have no problems on sub woofer duty.  It's not the class of output, it's the robustness of the design.
Yes, robustness of the design.  I had only heard/read about that issue with Class D, but never delved further into it.  For "bar sized" gigs, we use a JBL PRX718 (class D), it's seems fine for how it's used.
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Mike Goodreau

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Re: QSC PLD amps
« Reply #12 on: November 30, 2015, 11:23:16 am »

Yes, robustness of the design.  I had only heard/read about that issue with Class D, but never delved further into it.  For "bar sized" gigs, we use a JBL PRX718 (class D), it's seems fine for how it's used.

Our LabGruppen PLM 20000Q amps will really drive SB1001 subs well. The QSC has done OK on subs in 2 channel parallel mode. The price is a bargain, by comparison to Lab.
I guess I will order some more and keep good track of my warranty expiration date.
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Bob Lee

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Re: QSC PLD amps
« Reply #13 on: November 30, 2015, 12:54:12 pm »

I own a half dozen QSC PLD 4.5 and 4.2 amps and am considering buying more. I have had to replace 2 of these and wonder how they have performed for others? QSC has been good about servicing these but I certainly don't need more amp failures. Anybody have experience with these they want to share?

Reliability in the PLD amps has been a problem but over time has been getting a lot better as we adapt to more and more real-world experience with them.

If you have a PLD or CXD amp, please do the following to help ensure that it continues to work well:
  • Check the firmware. Update it if it is not the latest. You can download both the firmware and the Amplifier Navigator software (Mac or Windows) from the QSC website. Use a USB connection between the amp and computer. If you have multiple amps, you can use a USB hub to connect to all of them simultaneously.
  • Especially if it's an early production amp, note the serial number and contact QSC Technical Services Group to see if it should get some hardware updates as well. You can contact QSC TSG at tech_support@qscaudio.com, 1-800 QSC AUDIO (US and Canada only), or +1 714 957-7150.
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Bob Lee
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Brian Jojade

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Re: QSC PLD amps
« Reply #14 on: November 30, 2015, 12:58:18 pm »


    • Especially if it's an early production amp, note the serial number and contact QSC Technical Services Group to see if it should get some hardware updates as well. You can contact QSC TSG at tech_support@qscaudio.com, 1-800 QSC AUDIO (US and Canada only), or +1 714 957-7150.

    Is there a particular serial number sequence we should be looking for?
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    Brian Jojade

    Mike Goodreau

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    Re: QSC PLD amps
    « Reply #15 on: November 30, 2015, 02:01:12 pm »

      Is there a particular serial number sequence we should be looking for?
    Thanks for posting, Bob! Your help is appreciated.  I wish more manufacturers would get involved in the LAB.
    2 of my 4.5's were some of the first made. My amp and Navigator firmware is the latest, but I will check with tech support and see if there are more updates needed.  [/list]
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    paul bell

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    Re: QSC PLD amps
    « Reply #16 on: November 30, 2015, 03:06:53 pm »

    Yes, thank you Bob for hopping onboard here. You get a gold star!

    I bought one of the very earliest ones and it was recalled back to the factory. I was sent a replacement BEFORE sending the original back. QSC even included a shipping label.

    I believe they discovered a hardware issue in the design and needed to fix all of them so to avoid the problems they had with the 9.0, they requested all of them back.

    And QSC gets a gold star too!

    The one I have has been great also although I don't use it as often as I'd like to.
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    Mark Wilkinson

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    Re: QSC PLD amps
    « Reply #17 on: November 30, 2015, 03:14:09 pm »

    Yes, thanks for joining in...
    Just updated software and firmware.

    One thing i don't understand about the PLD's specs is the relationship between continuous and dynamic wattages at given loads and channels (dynamic used to be called burst) .
    Table is in here ...http://www.qsc.com/live-sound/products/power-amplifiers/pld-series/pld45/

    For instance, the 4.5 in 4 channel mode says, 1150 W Continuous vs 1200 W Dynamic, into 8 ohms.
    In 2 channel mode, 8 ohms is 2250 Continuous vs 4000 Dynamic.. (I assume 2 channel means parallel channels????)

    Why is there essentially zero headroom in 4 channel mode and nearly 3 db in 2 channel?
    And why does this headroom pattern vs channel utilization reverse itself into 4 ohm loads?

    Oh, and I guess I should really ask what exactly does dynamic wattage mean?
    Many thx




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    Corey Scogin

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    Re: QSC PLD amps
    « Reply #18 on: November 30, 2015, 04:25:24 pm »

    One thing i don't understand about the PLD's specs is the relationship between continuous and dynamic wattages at given loads and channels (dynamic used to be called burst) .
    Table is in here ...http://www.qsc.com/live-sound/products/power-amplifiers/pld-series/pld45/

    For instance, the 4.5 in 4 channel mode says, 1150 W Continuous vs 1200 W Dynamic, into 8 ohms.
    In 2 channel mode, 8 ohms is 2250 Continuous vs 4000 Dynamic.. (I assume 2 channel means parallel channels????)

    Why is there essentially zero headroom in 4 channel mode and nearly 3 db in 2 channel?
    And why does this headroom pattern vs channel utilization reverse itself into 4 ohm loads?

    I'll defer to Bob Lee's answer if he posts one and I'll of course defer to JR or someone else with real electronic circuit design knowledge but I'll venture to guess...

    In instances where the "dynamic" or "peak" power is very close to the continuous power, the power is likely limited by voltage not current. It may not be possible for the amplifier circuit to produce more than X voltage per channel but it can produce that X voltage all day long. This corresponds to the area to the right of each peak in the chart below.

    When more "dynamic" power is available the power is likely limited by current not voltage. Running over current rating for brief periods can be handled because it's mostly a matter of dissipating that extra heat over time. Continuous power is limited by the heat dissipation rate. This corresponds to the area to the left of each peak in the chart below.

    This chart is helpful to look at some of the relationships. You can see Ohm's law at play.
    « Last Edit: November 30, 2015, 04:39:55 pm by Corey Scogin »
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    Greg_Cameron

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    Re: QSC PLD amps
    « Reply #19 on: November 30, 2015, 04:35:49 pm »

    That's patently false.  Lab Gruppen, Crown I Tech and many other Class D amps have no problems on sub woofer duty.  It's not the class of output, it's the robustness of the design.


    FWIW, the output stage on the Labs is actually class AB. The "class D" section is actually just used to feed the high voltage rail for the output devices, not for audio. Said class D section tracks the incoming audio signal and supplies rail voltage as needed in tandem. I emailed Lab's engineers several years ago to understand what was really happening in their amps as they were calling them "class TD" instead of just "class D." Interesting stuff.
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    Cameron Pro Audio

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    Re: QSC PLD amps
    ¬ę Reply #19 on: November 30, 2015, 04:35:49 pm ¬Ľ


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