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Luke's basic amplifier tests


lukeamdman

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...but I ran into the issue again with bridged amps since in that configuration there isn't a "ground level" connection...

 

Aw nuts.  Yes I suppose bridged would be a problem.  It's too bad differential probes are so expensive.

 

Do those flukes have any kind of data out feature?  I know my cheapy tekpower does.  It's actually pretty decent.  I think it captures 10 samples per second if you pick low precision:

 

www.amazon.com/TP9605BT-Cellphone-Connection-Interfaced-Multimeter/dp/B00SGKR9FA

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  • 1 month later...

Looking at your previously posted results, you show resistance values of between 5 and 6 ohms at 40 Hz, which is much less than what you show here which is close to 15 ohms.  Unless I'm misinterpreting your data, the implication is that the currents you are measuring at the resonance are way higher than they should be.  Of course, one should expect some impedance difference in drive level, but I wouldn't expect it to be that far off.

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  • 5 weeks later...

I've been messing with the scope again this week and I think I (well not really me, but a suggestion from notnyt) found out why the Rigol was reading a little higher votages than the Flukes.  Here's what I measured before:

 

 

 

scopevsfluke1_zpsewqhvyit.png

 

 

 

 

scopevsfluke2_zps9t4r1weq.png

 

 

 

 

Apparently there's a High Resolution setting on the Rigol and that seemed to level the playing field between the scope and flukes.  I'm going to to re-test the above numbers and report back. 

 

Also, and it's unfortunate, but the 87V doesn't oscillate any less than the Fluke 115/117 at 10hz and 5hz...arggg.....

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Did some CEA burst tests for the first time.  This is on a single channel of a SP2-12K.

 

First I wired all eight 21s into a single 1.5ohm load and ran an impedance sweep in WT2:

 

All%208%20-%206-30_zps6fhavpzd.jpg

 

 

All%208_zpsw2jfqlbe.jpg

 

 

 

 

I did some CEA testing at 10hz (2.36ohm) and 20hz (3.54ohm).

 

 

10hz:

 

DS1Z_QuickPrint6_zps6e2fq6to.png

 

 

290Vpp = 102.5Vrms into 2.36ohm = 4,451w

 

 

 

20hz:

 

And I somehow deleted the first screenshot!?!?!?

 

Anyway, 358Vpp clean with no clip lights

 

358Vpp = 126.5Vrms into 3.54ohm  = 4,520w.  Also, the spec sheet for these amps says 127Vrms, so this test seems spot on. 

 

 

I then pushed 0.5db further and got 384Vpp and a brief flicker of the clip light.  Sure enough, tiny bit of distortion in the peak of the wave form:

 

DS1Z_QuickPrint4_zps5rrrgtro.png

 

 

DS1Z_QuickPrint5_zpsvp85dzzk.png

 

 

384Vpp = 135.7Vrms into 3.54ohm = 5,201w

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Luke... does this mean the testing you did with the Crown XLS was flawed?  I'm a bit over my head here so wanted to just double check if that was the case.

 

Those tests are good.  The "High-Resolution" thing did lower the voltage a bit, but for the voltages the XLS was putting it was probably only ~2v. 

 

For the CEA burst stuff I just tested, those are the starting resistances, and with a reactive load like my subs the resistance will go up with more power.  Think of those CEA numbers as a best case number. 

 

Maybe I should get some heater elements and a bucket!  That's was nice about a non-reactive load, the impedance doesn't change with frequency. 

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Those tests are good.  The "High-Resolution" thing did lower the voltage a bit, but for the voltages the XLS was putting it was probably only ~2v. 

 

For the CEA burst stuff I just tested, those are the starting resistances, and with a reactive load like my subs the resistance will go up with more power.  Think of those CEA numbers as a best case number. 

 

Maybe I should get some heater elements and a bucket!  That's was nice about a non-reactive load, the impedance doesn't change with frequency. 

 

Ok, thanks.  I was mainly making sure the XLS stuff was "close" since your testing somewhat invalidates the whole subsonic filter debate. For the sub I'm building now its ported too so it will need a subsonic filter, but I'm using EQ that would potentially go lower than 20hz

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Ok, thanks.  I was mainly making sure the XLS stuff was "close" since your testing somewhat invalidates the whole subsonic filter debate. For the sub I'm building now its ported too so it will need a subsonic filter, but I'm using EQ that would potentially go lower than 20hz

 

Absolute worst case those XLS numbers may be 45-50w high. 

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Absolute worst case those XLS numbers may be 45-50w high. 

 

Yeah... since I need 200-400 wpc max @ 8 ohm from the entire amp (ie bridged) I'm not worried....

 

I am thinking about a 2500 later on to maybe a HST-15 or 18 or some other larger sub in a sealed box trying to enter the depths of ULF but thats likely a pipe dream till my new home pipedream materializes.

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Now you're getting somewhere...WT2 and actual impedance curve FTW.

 

Torpedo amps are high current beasts...Are you going to repeat the tests on your other amps on hand?

 

I'll definitely test some other amps this way, BUT, I think I'm going to put together a non-reactive load with some heater elements and a bucket first.

 

A CEA burst happens way too fast for me to measure the current across my resistor with a DMM.  With a dummy load, since the resistance won't change with frequency or as the power increases (well, not NEARLY as much as a driver will), I won't have to measure the current during the actual testing.

 

Anyone have any input/disagreements with that?

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