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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB: The Classic Live Audio Board => Topic started by: Mike Goodreau on November 27, 2015, 05:30:07 PM
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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?
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So far, mine are working like champs; I have yet to have a failure with QSC amps, though I have only owned about 15 or so.
I have five of the PLD amps, mostly used this past season. They are solid performers, sound good, and sip electricity. Sorry to hear you have had some trouble.
Cheers,
Nils
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We have 2 of the 4.2 series. No issues. Though, ours are used exclusively for monitor duty.
What kind of failures are you talking about (hardware? software?).
The firmware updated on all the amps?
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We have 2 of the 4.2 series. No issues. Though, ours are used exclusively for monitor duty.
What kind of failures are you talking about (hardware? software?).
The firmware updated on all the amps?
One made loud popping noises, the other gave error messages saying "outputs shorted" and shut down repeatedly for no apparent reason.
They also sound awful when clipped. Ours primarily run monitors as well.
I have updated firmware regularly.
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They also sound awful when clipped.
Um, so? Don't drive amps to clipping. Ever. Problem solved.
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Um, so? Don't drive amps to clipping. Ever. Problem solved.
Try telling that to the tour guest engineers!! But that's the least of my worries. I saw one of the install version shoot flames out of it!
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One made loud popping noises, the other gave error messages saying "outputs shorted" and shut down repeatedly for no apparent reason.
They also sound awful when clipped. Ours primarily run monitors as well.
I have updated firmware regularly.
Which (4.5 or 4.2) did what?
May i ask what monitors / speakers you are driving?
I have two 4.5's that have given no trouble, albeit with very light use...
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With a very broad stroke of the brush...over the past 4 decades we have powered our systems with Crown, Crest, QSC and Lab Gruppen amplifiers. While QSC have not been my favorite overall, they proved to be the most reliable, have the best service/support and generally be the greatest bang for the buck of the lot. YMMV.
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With a very broad stroke of the brush...over the past 4 decades we have powered our systems with Crown, Crest, QSC and Lab Gruppen amplifiers. While QSC have not been my favorite overall, they proved to be the most reliable, have the best service/support and generally be the greatest bang for the buck of the lot. YMMV.
I have also been a longtime QSC user, with few real problems. These new ones make me nervous,however. The 4.2's drive highs in bi-amp monitors. EAW micro wedges or Worxaudio Max1.5m's. The problems have been with 4.5's driving lows in wedges or EAW KF 364 House speakers in passive mode.
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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.
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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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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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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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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 [email protected], 1-800 QSC AUDIO (US and Canada only), or +1 714 957-7150.
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- 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 [email protected], 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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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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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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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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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.
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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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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.
Very cool, Greg! Thanks for the 'amplification'. ;)
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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.
Thx Corey,
Yes, I've read and studied the FAST paper a few times, and hold the same views about current vs voltage constraints you describe.
But I still have a hard time fully tying the PLD 4.5 specs with the charts in the FAST paper.....particularly the dynamic vs continuous numbers.
And if you'll note the continuous 2 channel outputs vs the FAST graph you posted, the 8 ohm output can only be obtained bridging a pair of channels, while the 2 and 4 ohm outputs need to be paralleled.
Seems like this should be footnoted or something, because it appears that you really need to know which side of the 5.5 ohm single channel peak the amps will be pushing.... when you go to combine channels...
Also seems like this means the amp might have a bit of difficulty with subs that have relatively large minimum and maximum impedances ???
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Thx Corey,
Yes, I've read and studied the FAST paper a few times, and hold the same views about current vs voltage constraints you describe.
But I still have a hard time fully tying the PLD 4.5 specs with the charts in the FAST paper.....particularly the dynamic vs continuous numbers.
And if you'll note the continuous 2 channel outputs vs the FAST graph you posted, the 8 ohm output can only be obtained bridging a pair of channels, while the 2 and 4 ohm outputs need to be paralleled.
Seems like this should be footnoted or something, because it appears that you really need to know which side of the 5.5 ohm single channel peak the amps will be pushing.... when you go to combine channels...
Also seems like this means the amp might have a bit of difficulty with subs that have relatively large minimum and maximum impedances ???
Hi All,
As the Product Manager who along with our engineering staff developed the PLD amps, I will try to answer some of the lingering questions.
First of all Amplifier Design: Corey appears to have a good understanding of the principles that govern our Flexible Amplifier Summing Technology. To add to what he has said, all single amp channels (from any manufacturer) run up against two limiting factors, the voltage rails and the current limits. In the PLD we chose to put the Voltage/Current Peak right around 5Ω to make it more flexible. When the load is above this peak the power amp output typically runs out of voltage rail before it runs out of current limit, and when the impedance is below this peak it will run out of current capability before it runs out of voltage. What this means in real world applications is that in the case of an 8Ω (or higher) loads the PLD voltage rails (PLD4.5 Vrails are +/- 155V) are more than stout enough to support the majority of applications. If you do want or need larger voltage, you can bridge two channels like any other amplifier out there – resulting in massive 310V potential. When the load drops to 4Ω (or below) we recommend putting two channels in parallel, this doubles the current capability. Again, in real world applications, even if you don’t parallel the channel the amp will run just fine, but the current limiters will kick in and you may not get as much power as you might like. This is a bit simplified because current limiting is not a dead stop the way voltage rails are, so there is some short term additional power capability that you can get with transient material.
Secondly Software/Firmware: Yes, this is a DSP driven amp and like any DSP product, there are bugs found and firmware updates that will squash those bugs along with providing greater functionality. We always recommend that you run the latest software version.
Third, and probably the biggest one of all, Power Ratings: Due to the flexibility of our FAST channel combining it was nearly impossible to post the power ratings for all channel configurations in the given space so we had to come up with a way to show the flexibility as well as giving the reader some idea of the capabilities of this amplifier family. What I did, was I chose from the various configurations in 4CH, 2CH, and 1CH and posted the power for those. In some cases this was a parallel channel combination, and in others this is a bridged channel combination. Of course the other big issue is the fact that our industry has gone away from continuous power ratings to a more “Dynamic” power testing. I put dynamic in quotes because the actual test method is called “Burst” (using tone bursts meant to emulate an actual dynamic audio signal to measure power instead of a continuous sine wave). One of the problems that we have as an industry is that we all do these tests somewhat differently so you can see where that is headed. We are actually working on a project with the AES, Crown, and Lab Gruppen to create a standardized dynamic power test, but it may be a while before this is completed.
I hope that answers the majority of questions.
Thanks,
Dale
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Hi All,
As the Product Manager who along with our engineering staff developed the PLD amps, I will try to answer some of the lingering questions.
Please go to your profile and change the "Name" field to your real first and last name as required by the posting rules displayed in the header at the top of the section, and in the Site Rules and Suggestions (http://forums.prosoundweb.com/index.php/board,36.0.html) in the Forum Announcements section, and on the registration page when you registered.
Also, as a representative of a manufacturer, please include that affiliation in a sig line.
Mac
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Great information Dale! Thank you for posting!
You mention terms of "burst" and "continuous". What amount of "time" was used when speaking of burst or continuous ratings. For example, is "bust" time a 20ms unit of time? How much time references "continuous"?
Thanks again,
Bob
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Thanks for your reply Dale,
And also thanks for the information you provide in your white papers....they really help trying to understand.
I wish all the manufactures published the voltages and currents available, and design vs impedance curve.
I've been very happy using the pld4.5 to triamp a MF/HF/VHF box, paralleling two channels for the MF.
I also use the amp to drive a sub with 2 channels, and a two-way top.
So I do use it for subwoofer duty....and with today's high power LF drivers it's made me question things a little
One horn loaded sub I use with the amp has a couple of impedance minimums of about 3.5 ohms, and a couple of maximums at about 15 ohms, within a 30-100hz passband.
Unless I'm missing something, if I parallel two channels, the 15 ohm frequencies will have about 800 continuous watts available.
And if I bridge two channels, the 3.5 ohm freqs will have about 1100 watts available.
(I used 17.7arms from the FAST paper ....and 109vrms from your post, assuming the 155v you mentioned is peak????)
Either way, at certain freqs the sub will be getting less than half the power i might have expected from just glancing at specs.
(Maybe this sub has unusually high impedance peaks??? I certainly dunno...)
But all this to me begs...don't all amps have this trade-off going on?
And is this the gist of what makes a "good" sub amp? Or knowing what amps can give headroom to high-power high-impedance compression drivers?
Sorry if this has been too much of a tangent to the OP's reliability questions.. but might reliability be a function of suitably matching channel combining to the load..?
Thanks again, Mark
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Great information Dale! Thank you for posting!
You mention terms of "burst" and "continuous". What amount of "time" was used when speaking of burst or continuous ratings. For example, is "burst" time a 20ms unit of time? How much time references "continuous"?
Thanks again,
Bob
Hi Bob,
Continuous power testing is a great way to find the long-term thermal capacity of the amplifier but it isn't the best way to measure the real-world power capability that can be put into an loudspeaker. When we do continuous power testing we typically do either an FTC or an EIA power test (sometimes both). Continuous power testing is done long term (many hours), so the the amp is essentially at steady state and will run indefinitely at those ratings.
Our burst power testing (I prefer the term Dynamic Power Testing) is done using a 30ms sine wave tone burst. These types of signals do a better job at emulating the duty cycle of dynamic music (LF in particular).
Thanks,
Dale
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I've been very happy using the pld4.5 to triamp a MF/HF/VHF box, paralleling two channels for the MF.
I also use the amp to drive a sub with 2 channels, and a two-way top.
So I do use it for subwoofer duty....and with today's high power LF drivers it's made me question things a little
One horn loaded sub I use with the amp has a couple of impedance minimums of about 3.5 ohms, and a couple of maximums at about 15 ohms, within a 30-100hz passband.
Unless I'm missing something, if I parallel two channels, the 15 ohm frequencies will have about 800 continuous watts available.
And if I bridge two channels, the 3.5 ohm freqs will have about 1100 watts available.
(I used 17.7arms from the FAST paper ....and 109vrms from your post, assuming the 155v you mentioned is peak????)
Either way, at certain freqs the sub will be getting less than half the power i might have expected from just glancing at specs.
(Maybe this sub has unusually high impedance peaks??? I certainly dunno...)
But all this to me begs...don't all amps have this trade-off going on?
And is this the gist of what makes a "good" sub amp? Or knowing what amps can give headroom to high-power high-impedance compression drivers?
Sorry if this has been too much of a tangent to the OP's reliability questions.. but might reliability be a function of suitably matching channel combining to the load..?
Great questions Mark,
Yes, every single amplifier out there has the same issues, balancing Low-Z current performance with high-Z voltage performance; the difference that we offer with the PLD amps is the ability to parallel channels for high current output.
Yes, reliability is absolutly a function of matching the drivers with an amp that can drive them well. Not to toot our own horn, but one of the major successes of the QSC K Series has been how well matched the drivers were to the amplifiers and vice versa - it creates a very robust system that repeatably sounds great.
If it were me, I would error on the Low-Z side of the impedance curve and parallel the channels. With a 155V rail there is almost always enough voltage to push a high impedance load but current limiting will steal your thunder. Yes, you can get quick transients through the current limiter, but with LF content there can be a lot of them and so at some point either the thermal or current limiter is going to kick in. When you parallel channels you have twice the current capability. Our own testing at QSC has shown me time and again that while bridging can be useful in some applications, paralleling outputs (especially with subwoofers) often produces more useful output. If you are using the latest firmware I would recommend you do your own testing and see. You will not hurt the amp to run into the current limiter, nor will you hurt it if you bridge into a 4 ohm load, in either case if you run into trouble the limiters will protect you.
Thanks,
Dale
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Hi Bob,
Continuous power testing is a great way to find the long-term thermal capacity of the amplifier but it isn't the best way to measure the real-world power capability that can be put into an loudspeaker. When we do continuous power testing we typically do either an FTC or an EIA power test (sometimes both). Continuous power testing is done long term (many hours), so the the amp is essentially at steady state and will run indefinitely at those ratings.
Our burst power testing (I prefer the term Dynamic Power Testing) is done using a 30ms sine wave tone burst. These types of signals do a better job at emulating the duty cycle of dynamic music (LF in particular).
Thanks,
Dale
This is like RMS, program, and peak ratings of the speaker. If you design your system so that within the continuous rating of the amp you are at or below the RMS rating of the speaker and you can achieve the maximum volume needed for your event, you will almost never have to worry about blown equipment. Thrown in low pass filters to prevent mechanical over excursion and you can create a system nearly DJ proof. :)
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Hi Bob,
Continuous power testing is a great way to find the long-term thermal capacity of the amplifier but it isn't the best way to measure the real-world power capability that can be put into an loudspeaker. When we do continuous power testing we typically do either an FTC or an EIA power test (sometimes both). Continuous power testing is done long term (many hours), so the the amp is essentially at steady state and will run indefinitely at those ratings.
Our burst power testing (I prefer the term Dynamic Power Testing) is done using a 30ms sine wave tone burst. These types of signals do a better job at emulating the duty cycle of dynamic music (LF in particular).
Thanks,
Dale
Looks good. Thanks Dale.
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Dale, your advice is appreciated.
One last question....when updating Navigator, I saw the latest release notes mention FIR filter capability.
How is this accessed?
Thx, Mark
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Dale, your advice is appreciated.
One last question....when updating Navigator, I saw the latest release notes mention FIR filter capability.
How is this accessed?
Thx, Mark
Bob/ Dale,
I too am interested in the answer to this question. Although, after previously sending a similar query to technical support with no response, I have a feeling I know the answer.
This would greatly increase their value to me, and I am sure for others as well, as many other manufacturers have allowed end users access to such features (e.g. powersoft, ashly, symetrix, bss, etc...) presumably based on a need. C'mon, all the cool kids are doing it. 8)
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I've have been looking at PLD4.5 for some time now and can't find any specs on the power rating for 3 channels in parallel running a 4 ohm load. Does anyone know where to find that?
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I've have been looking at PLD4.5 for some time now and can't find any specs on the power rating for 3 channels in parallel running a 4 ohm load. Does anyone know where to find that?
Page 15-16 of the user manual:
http://www.qsc.com/resource-files/productresources/amp/pld/q_amp_pld_usermanual.pdf
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We are in the process of testing PLD's. Application will be concert line array hangs. We're lucky enough to have a shop that permits the rigging of a "shop" stereo. Each hang needs 2 speaker lines for the L, M, & H. All of the 12 loads (6 Left and 6 Right) are a nominal 4 Ohm rated impedance. Right now we've got a 4.5 on lows, a 4.3 for the mids, and a 4.2 powering all 16 HF drivers. Again, each channel of each amp is loaded with 4 Ohms.
BTW, we've performed many amplifier "tests" over the years.
These amps sound fantastic. We are very impressed. It's been a long time coming for an amplifier upgrade / replacement for our rigs. These amps are the first amps that pass the test - for us. Other manufacturers charging $0.50 plus per Watt have not been contenders. We've just lugged the heavy amps, and enjoyed their tried and true sonic abilities. Enter the PLD's.... We're buying some.
We've installed some of these amps in their CXD format and obtained good results. Time this March has allowed for this 2 week test. We did test a 4.3 last winter and particularly liked its control over the subs on which we tested it. Our shop system has 6 21's handling the sub duty. I'll report the results of moving the 4.5 to the subs ( all 6 4-Ohm loads) and also making the 4.3 handle the lows and mids; which will load the 4.3 with 2 Ohm loads!
One more thing, we'll buy only 4.5 models. The 4.2 doesn't quite handle the highs at full full volume. While the 4.3 would, it just makes sense to buy all 4.5 models. Why not?
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We are in the process of testing PLD's. Application will be concert line array hangs. We're lucky enough to have a shop that permits the rigging of a "shop" stereo. Each hang needs 2 speaker lines for the L, M, & H. All of the 12 loads (6 Left and 6 Right) are a nominal 4 Ohm rated impedance. Right now we've got a 4.5 on lows, a 4.3 for the mids, and a 4.2 powering all 16 HF drivers. Again, each channel of each amp is loaded with 4 Ohms.
BTW, we've performed many amplifier "tests" over the years.
These amps sound fantastic. We are very impressed. It's been a long time coming for an amplifier upgrade / replacement for our rigs. These amps are the first amps that pass the test - for us. Other manufacturers charging $0.50 plus per Watt have not been contenders. We've just lugged the heavy amps, and enjoyed their tried and true sonic abilities. Enter the PLD's.... We're buying some.
We've installed some of these amps in their CXD format and obtained good results. Time this March has allowed for this 2 week test. We did test a 4.3 last winter and particularly liked its control over the subs on which we tested it. Our shop system has 6 21's handling the sub duty. I'll report the results of moving the 4.5 to the subs ( all 6 4-Ohm loads) and also making the 4.3 handle the lows and mids; which will load the 4.3 with 2 Ohm loads!
One more thing, we'll buy only 4.5 models. The 4.2 doesn't quite handle the highs at full full volume. While the 4.3 would, it just makes sense to buy all 4.5 models. Why not?
Were you able to drive the amps hard and judge their performance ?
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One more thing, we'll buy only 4.5 models. The 4.2 doesn't quite handle the highs at full full volume. While the 4.3 would, it just makes sense to buy all 4.5 models. Why not?
For tri-amp rigs I used to have the highest wattage amps for the subs, medium wattage for the lows, and lowest power for the mid/highs. But that meant carrying a spare of each.
These days I prefer identical model amps in the rack, each amp having all the presets I'll need (e.g. subs, low, mid/high.) Then just dial the appropriate preset and LOCK the front panel. If a mid/hi amp goes down, I can temporarily take one of the amps for the subs and get going in a couple of minutes. I still bring a spare, but just one, and it sits in the truck. So I think your logic of having all PLD4.5 makes perfect sense. Price difference between 4.3 and 4.5 is not so significant.
I've installed quite a few PLD4.3 and 4.5 -- they are light, great sounding amps and have been very reliable. The fans are quiet, but for longevity sake I just wish those fans don't run continuously (they run even when there's no input signal.)
John R.
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I test amps from the lowest level imaginable and also with the red lights on steady. The gain structure was matched to our normal amp racks. This was achieved at the PLD's input gain adjustment. The amp's limiters were set wide open (maximum power). We hit red on the highs, even with the loudspeaker controller doing its limiting. Again, the PLD4.2 is simply less power than what is needed for that duty. Red lights on the other amps were only obtainable by defeating the loudspeaker controller's limiters. We say amperage draws as high as 20A on the lows and upper teens on the mids.
The fans running continuous is bothersome; however, the amp does draw 0.8 Amps at idle. There must be a component requiring some airflow.