Jump to content
lukeamdman

Luke's basic amplifier tests

Recommended Posts

...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

Share this post


Link to post
Share on other sites

Received the Smith and Larson WT2 today.  Neat!

 

This is certainly a lot easier than doing impedance sweeps one frequency at a time with a pair of DMM!  lol

Share this post


Link to post
Share on other sites

Good, now we can see peavey numbers :-p

 

Today is the day!  Getting things setup to test it right now. 

 

4ohm 1ch driven

4ohm both ch driven

8ohm bridge

frequency response

Share this post


Link to post
Share on other sites
On 5/27/2016 at 11:45 PM, Stormwind13 said:

Good, now we can see peavey numbers :-p

 

Peavey 4080 is a beast!

 

jgD2Nk8.jpg

 

 

Testing done at 20hz. 

  • Like 3

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.....

Share this post


Link to post
Share on other sites

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

  • Like 1

Share this post


Link to post
Share on other sites

Nice.  Hopefully spreading the power out across a lot of drivers helps minimize the impedance changes that occur.  How much excursion do you think the drivers were seeing for these tests?

Share this post


Link to post
Share on other sites

Nice. Hopefully spreading the power out across a lot of drivers helps minimize the impedance changes that occur. How much excursion do you think the drivers were seeing for these tests?

For 10hz maybe 1/2"?

Share this post


Link to post
Share on other sites

Here's a test notnyt wanted me to run on a channel of the 12k.  

 

20hz at 3.5ohm for 12 seconds:

 

DS1Z_QuickPrint1_zps23hguu7b.png

 

 

 

DS1Z_QuickPrint2_zpszxr05io3.png

 

 

 

Maintains 356Vpp (125.8Vrms / 4,521w) for the entire 12 seconds...

 

Amp ice cold, fans idle.  

  • Like 1

Share this post


Link to post
Share on other sites

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. 

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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. 

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites

Here's an updated comparison between the scope and the flukes now that high resolution is turned on.

 

scopevsfluke_v2_zpsbu1k6pwy.png'

 

 

The 87V definitely has less fluctuation than the 117, but at 5hz it's still not great.  

Share this post


Link to post
Share on other sites

How much power do you plan to put into one of those?

 

There will be 5 per channel, so the most power one should see is about 1,200w for 4-5 seconds. 

 

They'll be in a 5 gallon bucket of water as well.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×