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[Nathan Short]

The bucket was set up to run 2 elements per load in parallel.  4ohm.

I will go ahead and type up my full measured list for the 3602.

since the amp has no "0" level the near "0" measurement was set to at "no clip" "solid -6"  The second measurement was taken as an average of moderate clip light flashing, but not solid or heavy.

It will go as follows  Noise     Vat"0"/V at "clip",  amps/amps

Pink 6db crest    33v/45v    15a/21a
30Hz              na   /60v     na  /33a
50Hz              40v/60v     24a/33a
85Hz              50v/60v     27a/32a
1kHz              45v/60v     24a/31a
15kHz             na/na          33a
Dance Music    
Light ,hard, limit   20v/41v/50v    10a/21a/26/

[Mac Kerr]

Nathan Short wrote on Mon, 22 February 2010 16:21

since the amp has no "0" level the near "0" measurement was set to at "no clip" "solid -6"  The second measurement was taken as an average of moderate clip light flashing, but not solid or heavy.

This would have been a lot more useful if instead of "no clip" and "solid -6" that have no real reference you measured the actual input voltage and the actual output voltage at each frequency, and looked at the waveform on a scope to determine the onset of clipping. The actual input and output voltages at clipping at each frequency would also be good to know, as would the line voltage at each point.

If you are going to all the trouble of making measurements you may as well make complete measurements.

Given complete information on the test procedures Bob could duplicate the test on another amp and perhaps tell you whether your amps are broken or if it is a problem in the deign (or not).

Mac

[Elliot Thompson]

Nathan,

I don’t see anything wrong with the amplifier. If you look below QSC states the PLX 3602 will draw 33 amperes when you feed it sine waves.

If the PLX 3602 was drawing 33 amperes, that would equate to 3960 watts on a 120-volt line source. It seems to me it exceeds
it's advertised wattage of 3600.  






Best Regards,

[Art Welter]

Nathan Short wrote on Mon, 22 February 2010 14:21

The bucket was set up to run 2 elements per load in parallel.  4ohm. I will go ahead and type up my full measured list for the 3602. since the amp has no "0" level the near "0" measurement was set to at "no clip" "solid -6"  The second measurement was taken as an average of moderate clip light flashing, but not solid or heavy. It will go as follows  Noise     Vat"0"/V at "clip",  amps/amps Pink 6db crest    33v/45v    15a/21a 30Hz              na   /60v     na  /33a 50Hz              40v/60v     24a/33a 85Hz              50v/60v     27a/32a 1kHz              45v/60v     24a/31a 15kHz             na/na          33a Dance Music     Light ,hard, limit   20v/41v/50v    10a/21a/26/

Nathan,

I can’t tell from what you wrote if these test results are both channels driven at 4 ohm, or just one channel.

Also, the PLX 3602 has no -6 indicator, it has SIG, -10 and CLIP.

The 60v sine wave figures you posted above would be a bit below the 1100 rated 20-20kHz output, 60 v at 4 ohm would be 900 watts.

By the current draw and output voltage you state, sounds like you were not quite hitting clip.
Always a question whether an amp’s clip lights come on a bit before or a bit after onset of clipping, from my experience with the PLX 3602, they come on before, but that is just “by ear”.

As Elliot pointed out, the PLX 3602 specifications state that with both channels driven with sine wave, it draws 25 amps at 8 ohms, 40 at 4 ohms, 63 amps at 2 ohms.

Back to the previous anomaly causing your concern, 81 volts into 2 ohms would be about 3280 watts, not an “abnormal” amount if the amp was hard clipping, 60 volts would be 1800 watts at 2 ohms, less than a 3 dB difference.
An amp producing a square wave can produce almost double the power output as a sine wave.

33 amps at 120 volts would not be out of line for 3280 watts delivered, 82.7 % efficiency.

Granted, both sides should perform the same, but the difference sounds like it could be a funky Clip Limiter on /off switch, with the limiter engaging on channel 2, but not on channel one.

The limiter only responds to actual clipping. When the limiter is engaged, the CLIP light indicates both clip and limit.

Art Welter

[Bob Lee (QSC)]

Nathan, you keep saying that one channel behaved normally but you don't tell us how you define that.

And you complain that one channel will put out 81 volts, which is entirely possible. With no load and a normal mains voltage, yeah, it'll probably clip at around 81 V rms. With a load it'll clip at a lower voltage but can put out a higher RMS voltage by running it into clipping. You don't tell us anything about that 81 volts, like whether it's clipped or not, whether below clipping it's proportional to the input signal

[Nathan Short]

Hey guys, I am ordering this http://www.syscompdesign.com/OrderStep1.html

I have heard great things about it.  

Once I have my scope set up, I should be able to very much further refine my process.  

Thanks for all the replies, but this is beating a dead horse now.  The people who obviously have the rest of the proper testing equipment I do not have, want answers I cannot give them at this time.  I am slowly building my equipment up.

Maybe we could approach this more constructively with a full set of amps from various brands, and set some sort of "real world" standard.

I approached this out of frustration from what I believe to be inflated specs from manufacturers.  And wanted to gather my own tables of real output voltage at common levels of use and abuse.

IE see the performance of low and high level gear in my own situation.  

Plain and simple 3602 has an issue.  So I will be happy and glad to continue putting PL340's and 380's on my rigs.  They are rock solid, and a joy to work with.  

[John Roberts {JR}]

Nathan Short wrote on Mon, 22 February 2010 20:19

Hey guys, I am ordering this http://www.syscompdesign.com/OrderStep1.html I have heard great things about it.

I'm not familiar with that brand.. USB scopes range all over from crap to OK. You can probably get a real scope used for that, but if you know folks who have checked that one out and like it, go for it.  

Quote:

Once I have my scope set up, I should be able to very much further refine my process.   Thanks for all the replies, but this is beating a dead horse now.  The people who obviously have the rest of the proper testing equipment I do not have, want answers I cannot give them at this time.  I am slowly building my equipment up. Maybe we could approach this more constructively with a full set of amps from various brands, and set some sort of "real world" standard. I approached this out of frustration from what I believe to be inflated specs from manufacturers.  And wanted to gather my own tables of real output voltage at common levels of use and abuse.

Please understand and take this the right way. There is frustration also from amp makers, some who have had to deal with uninformed criticisms for decades about amp specs with suggestions that the amp makers are dishonest.

I applaud you willingness to educate yourself and folks here will help you, but I would suggest a starting from a more neutral premise than manufacturer's specs are "inflated".  

Quote:

IE see the performance of low and high level gear in my own situation.   Plain and simple 3602 has an issue.  So I will be happy and glad to continue putting PL340's and 380's on my rigs.  They are rock solid, and a joy to work with.

I would also suggest doing a search and checking out the power amp test series that Bink did several years ago. There was a great deal of useful information in the advance work, and I probably wrote too many words on the subject of possible new ways to characterize duty cycle for audio amps.

Good luck. I expect you'll find this isn't as simple as you suspect.

JR

PS: You are starting from a good place with a good distro (I think). That is a common mistake made by many who blame their amps for things caused by bad mains power. Of course the scope will be useful to help confirm the quality of the mains too.

[Brian Seefeldt]

Nathan Short wrote on Mon, 22 February 2010 20:19

Plain and simple 3602 has an issue.  So I will be happy and glad to continue putting PL340's and 380's on my rigs.  They are rock solid, and a joy to work with.

Well...I'll buy Bob Lee and the guys @ QSC a beer anytime.
I have (4) 3602's and they have been damn near flawless for 3.5 years. (1 had a power supply go down) It was fixed under warranty,
(Very quickly i might add)
And these are amps that do not live in a perfect studio environment. There out working sometimes 4-5 nights a week.

I will be buying 2 more here very shortly.

[Bob Lee (QSC)]

Nathan, what do you mean by "current management"? The PL340 doesn't have any "current management" that the PLX3602 doesn't have. They're actually very similar in their core power supply and audio circuitry, and differ mainly in the features. You can download and compare the schematics if you like.

[Nathan Short]

Sorry Bob,

As I am not an EE, this is just a losing conversation for me.

I wish you would be more helpful, but at the same time, I guess that other people have actually helped me more understand what I am trying to explain, so all in all, I have my answers.  

To put it better.  The PL380 and 340 both do excellent jobs of only drawing a certain ammount of amperage under a heavy load.
They do their jobs well, and with repeatable results that satisfy my needs.  

And to be very hones, I have had zero failures of PLX and PLX2 in the last 7 years. Good power, good ventilation, and proper wiring on the installs, and bam the amps do their job.

The 3602 testing I did just confirmed my personal experience that every now and then, with the right DJ doing the right thing.  Ch1 will blow a VC right out of the basket, while Ch2 will not.  Clip limiter on Ch1 not effective. But who knows.  Evidently not me.