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Old 15th January 2008, 01:39 AM   #21
Eva is offline Eva  Spain
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A few years ago I used to work for a local band that had a few Peavey CS-800 in their PA setup, and other similar amplifiers. I mean the good old CS-800, the one with the fashion die cast front plate using 5U rack space and weighting approx 20Kg. It was really heavy and bulky for an amplifier producing only 250W per channel at 8 ohm and 400W at 4 ohm.

I can assure that carrying that kind of gear back and forth (truck, stage, truck, stage...) teaches you some very valuable lessons about amplifier design that can't be found on any text book or forum. Every amplifier designer should go through this experience.

I wish I had the class D knowledge that I have now back then... Now I'm working on reasonably "portable" stuff capable of producing 2KW or 3KW without even a fan
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Old 15th January 2008, 02:18 AM   #22
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I love my QSC's, I have 3 of the PLX1804 amps. thats 5.4kw of power. in 6 rack spaces and the whole things weighs under 40lbs!!!!

Thats HALF the weight of ONE old school amp! and you just got to love an amp that puts out 900 watts per channel at 4 ohms and weighs 13LBS!!!!

Not to mention that QSC has a KILLER employee Dealer program that allows people that work for QSC dealers to buy there amps and a huge discount. I got mine for half of street retail!

Not to mention QSC has the best support of there products! They even have an online forum for techs to talk to REAL techs about servicing there amplifiers. and not "just send it in" i mean, check q102 and r13 and voltages should be type real help. NO ONE else in the biz has that.
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Old 15th January 2008, 03:48 AM   #23
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I have a strong feeling that we have some of the staff members from QSC sales dept here on this very thread..........

This PL380 features all smd construction, good for marketing hype, but not that much reliable when it comes to survive transportation jobs loading, unloading. I have seen many bad smd components displaced/broken pcb pads just due to vibration on plx3602.

Evita this amplifier conducts huge EMI, we had it tested on live stage and found that it interferes greatly with cordless mics which are working in VHF band. Their is no proper uniform groundplane on the PCB, but it still amazes me that this thing uses 4-Layer board. . The Filter Toroids are mounted very near to the analog signal processing pre-amp opamps, therefore all the small-signal traces are highly contaminated. Idle Rails are +/-190V sag to 120V when subjected to 100mS brust of 1KHz at 2 ohms load. I can't understand how they are stating 4KW@2ohms per channel.
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Old 15th January 2008, 03:51 AM   #24
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Quote:
Originally posted by fredos
Still stable with no load? What happen if you drive it, maybe at 30% of full power and remove load? And if you drive it at HF and remove load? Just curiosity...

Fredos
They have used an aluminium encapsulted heatsink mounted 4.7E 200W resistor in Zobel just for that purpose............


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Old 15th January 2008, 05:11 AM   #25
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Quote:
Originally posted by Workhorse
Idle Rails are +/-190V sag to 120V when subjected to 100mS brust of 1KHz at 2 ohms load. I can't understand how they are stating 4KW@2ohms per channel.
yeah ... that is very suspicious indeed

from the layout it doesn't look like the amp was built from the ground up to deliver 8000 watts but rather looks like they simply took a PLX 3600 and turned it into a class D amp with some boost in output resulting from it

maybe they took 3600 watts multiplied by 85% efficiency and divided by something like 40% efficiency and declared that the new amp is thus 8000 watts lol ...

does anybody have an image of an I-Tech 8000 internal layout to compare this with ?
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Old 15th January 2008, 08:33 AM   #26
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Have a look on this: PowerSoft 2 x 9kw @ 2ohm....
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Old 15th January 2008, 11:42 AM   #27
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according to the website specs. the PL380 is rated for 2500 watts P/Ch at 4 ohms. and there is a note by the 2 ohms spec of 4000 watts that says *Burst mode testing required due to AC service current limitations.

So assume a very very short burst at that. what maybe 10-100ms or something? I wouldn't consider this to be a 4Kw per channel amp by any means. 2.5K yes.

Where do you find the 100 amp spec? i see a current draw listing of 18amps and there is a not that talks about a 30 amp cutback circuit. but im not sure where the 100 amp spec came from???



Zc
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Old 15th January 2008, 12:07 PM   #28
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The best way to understand this subject it to measure amplifier current consumption (peak and average) under real world working conditions (speakers and music). I encourage everybody to do so. Results have little to do with the assuptions commonly made by most people in these forums.
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Old 15th January 2008, 01:28 PM   #29
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Quote:
Originally posted by Zero Cool
according to the website specs. the PL380 is rated for 2500 watts P/Ch at 4 ohms. and there is a note by the 2 ohms spec of 4000 watts that says *Burst mode testing required due to AC service current limitations.

So assume a very very short burst at that. what maybe 10-100ms or something? I wouldn't consider this to be a 4Kw per channel amp by any means. 2.5K yes.

Where do you find the 100 amp spec? i see a current draw listing of 18amps and there is a not that talks about a 30 amp cutback circuit. but im not sure where the 100 amp spec came from???



Zc
What I read:
http://www.qsc.com/products/amps/pow...owerlight3.htm
Per channel it's rated.
4000*
EIA 1 kHz 1% THD
* Burst mode testing required due to AC service current limitations

And from: http://www.qsc.com/pdfs/manuals/PL3_...anual_RevB.pdf
Look for the table under "AC Mains Current Draw"
Which shows 2 x 2ohms at 100A for "Full Power Sine Wave"

So it's "EIA", and they may be on the loose side of the standard. I wonder what it would be for "FTC"? At least they're measuring to a standard.
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Old 15th January 2008, 01:38 PM   #30
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Ultimately I have no problem with designing a product to meet certain application specific performance requirements. However it is a slippery slope made even more slippery when the marketing people get their hands on things.

"Burst mode testing required due to AC service current limitations."

"Idle Rails are +/-190V sag to 120V when subjected to 100mS brust of 1KHz at 2 ohms load."

Put the two together and the first one needs to be restated as.

"Burst Mode testing required due to shoddy design of the SMPS operated open loop because we don't know how to design one and ripped off what everyone else is using"

Look at the flash presentation again.....

http://www.qsc.com/products/amps/pow...PL380_tour.htm

Can you see any output filter inductors in the power supply itself. You can't because they are not there. They are not there because the pro-audio johnnies don't have a basic clue. Let's not talk about capacitor lifetimes when you hammer them with extreme ripple currents.

Pre filter feedback indeed.

Someone else has mentioned EMC performance. The flash presentation proudly announces measures taken to deal with such issues. They don't work because the pro-audio johnnies don't have a basic clue.

I wouldn't push things but this might degenerate into another Nu-Force thread.

I'm a coward so I'll run away now.

DNA
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