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Discussion Starter · #1 ·
Here is a master index to all amplifier tests:


Behringer EP1500 8 ohm http://www.avsforum.com/avs-vb/showt...4#post10747784

Behringer EP1500 4 ohm http://www.avsforum.com/avs-vb/showt...2#post10748192

Behringer EP1500 2 ohm http://www.avsforum.com/avs-vb/showt...0#post10749440

Behringer EP1500 mono http://www.avsforum.com/avs-vb/showt...8#post10749998

Behringer EP2500 8 ohm http://www.avsforum.com/avs-vb/showt...3#post10753603

Behringer EP2500 4 ohm http://www.avsforum.com/avs-vb/showt...8#post10753638

Behringer EP2500 2 ohm http://www.avsforum.com/avs-vb/showt...7#post10755537

Behringer Ep2500 mono http://www.avsforum.com/avs-vb/showt...5#post10755565

Buttkicker BKA1000-4A 4 ohm http://www.avsforum.com/avs-vb/showt...6#post11032546

Buttkicker BKA1000-4A 2 ohm http://www.avsforum.com/avs-vb/showt...6#post11036186

O Audio 500 watt Plate Amp http://www.avsforum.com/avs-vb/showt...0#post11318800

Crown K2 8 ohm http://www.avsforum.com/avs-vb/showt...4#post11650994

Crown K2 4 ohm http://www.avsforum.com/avs-vb/showt...0#post11651100

Crown K2 2 ohm/mono http://www.avsforum.com/avs-vb/showt...0#post11660630

Crown K2 2 ohm 20 Hz http://www.avsforum.com/avs-vb/showt...9#post11661239

Crown XS900 8 ohm http://www.avsforum.com/avs-vb/showt...0#post12245500

Crown XS900 4 ohm/2 ohm http://www.avsforum.com/avs-vb/showt...1#post12245581

Crown XS900 mono http://www.avsforum.com/avs-vb/showt...6#post12246356

QSX PLX3402 8 ohm http://www.avsforum.com/avs-vb/showt...0#post12937520

QSC PLX3402 4 ohm/2 ohm http://www.avsforum.com/avs-vb/showt...8#post12938838

QSC PLX3402 mono http://www.avsforum.com/avs-vb/showt...1#post12939321

Dayton HPSA1000-R 8/4 ohm http://www.avsforum.com/avs-vb/showt...9#post13714349

Crown XTi1000 8/4/2 ohm http://www.avsforum.com/avs-vb/showt...6#post13869426

Crown XTi1000 extra http://www.avsforum.com/avs-vb/showt...4#post13877614

ED eQ.2 FR/distortion http://www.avsforum.com/avs-vb/showt...3#post13935023

ED eQ.2 filter response http://www.avsforum.com/avs-vb/showt...4#post13935034

Velodyne SC-1250 8/4 ohm http://www.avsforum.com/avs-vb/showt...9#post13990239

Audiosource AMP One http://www.avsforum.com/avs-vb/showt...9#post14135949

Techron 8506 http://www.avsforum.com/avs-vb/showt...5#post14230385

Peavey IPR-600 http://www.avsforum.com/avs-vb/showt...2#post18534472


I am starting a thread to post my measurements of various amplifiers that I own and that my friends own. I am posting this in the DIY forum because most of the amps are 2 channel professional power amplifiers like the type used in powering DIY subwoofers. I will also be emphasizing low frequency response measurements for these amplifiers.


The first few posts by me will lay out the methodology I am going to follow in measuring these amplifiers and the test equipment being used. I will be measuring power output in watts RMS, power output into various impedances (2, 4 and 8 ohms), THD+N or Total Harmonic Distortion, frequency response, and S/N ratio.


The first set of measurements I take will consist of duplicating what the manufacturer says the amplifier can produce, in other words, will it do what it says on the side of the box! After that, I want to see what it will do at maximum performance and, for instance, what the amplifier will do at 5 or 10 Hz.


Chuck
 

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Discussion Starter · #2 ·
Here is a list of the test equipment being used to perform the measurements.


The AC voltage must be constant and able to be regulated to compensate for line voltage variations. I am using a Superior Electric 136B Powerstat Variac. It is rated at 0-140 Volts AC and 22 amps continuous current. I have also built a digital voltmeter and ammeter to be able to adjust the AC voltage under load and measure the AC current being drawn by the DUT (Device Under Test). The voltmeter is capable of reading up to 600 VAC and the ammeter has the capability to read 50 amps AC current.




I have built a load bank and a load bank controller that I will be using to test the output of the amplifiers into constant known impedances. It is capable of switching between 2 ohms, 4 ohms, 8 ohms, and a totally open circuit. The power capabilities of the load start at 3500 watts RMS and have the capability of going up to 14,000 watts for checking those monster bridged mono units. The unit is water cooled.





The test equipment being used to generate the sine waves and measure the distortion are all made by Tektronix. I am using a SG505 sine wave oscillator that is capable of .0008% distortion from 10 Hz to 100 KHz, a SC502 15 MHz oscilloscope to view the distortion components of the DUT, an AA501 audio analyzer that has the capability of reading below .002% THD+N, a DC503A frequency counter that will measure from .01 Hz to 125 MHz. I am also using a Phillips PM3218 2 channel 35 MHz delayed time base oscilloscope to view the output waveform directly from the amplifier.




I am also using some switching components and a dual channel signal pad for setting levels on the amplifiers. The switching unit and the pad do not add more than .0002% THD+N to the overall measurements. All the interconnect cables are made by Pomona Electronics.





Chuck
 

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I am very interested in what you have to share. I know nothing about testing, that is why I turn to this forum to figure out what is the best bang for the buck.


Thanks for your efforts.
 

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More info on your resistor. Is it essentially metal rods of a givin resistance submerged in water?


*EDIT*

Ok, to not only help myself, but also others, I'm going to attatch come of Chasw's pictures. I can only attatch 10 pictures though.



















PLX 3402 Bridged



PLX-3402 stereo
 

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Awesome, having seen the set-up myself a few times, I can't wait for the info to be gathered. Looneybomber, his load bank is a bunch of heating elements (I think) in a 5 gallon bucket of water.



BTW, I sent you a pm a while back about prices of isolating transformers, don't know if ya read it.
 

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Friendly reminder. lol


Run the amp at lower power for a while to preheat your load as load resistance rises

with heat which make the power scores much better than it is. Preheat the load for

a while, then remove the load connections and use your DMM to verify that it's 2, 4 or

8 ohm. You don't want wacko load readings like 2.6, 4.7, 9.3 ohms, lol .. If you get

wacko readings like this, then your load is not stable.


Full power test. After you take your measurements, immediately use the DMM to take

load resistance readings. The readings can be higher as you crank up the power output.

Use these measured reading for the power calculation, ie if your load was stable in pre-flight and measured 2.1 ohms, but the full power test read 2.3 ohms, then use 2.3 ohms for final power calculation.


This is how other people fail when conducting amps tests, they don't follow this procedure

and the amp looks sweeter than it is.


For example.


You measured 50v rms and your load is really 4.0 ohms. That is 625 watts calculated.


But if the load was really 6 ohms during the test {due to heat}, the amplifier voltage

will be higher because the load is lighter, you may read 60v rms. Then you assume

the load is 4 ohms. That is 900 watts calculated.


Huge discrepancy that favors the amp because the load was not stable.


Last issue. Forcing the input AC voltage to 120VAC or whatever the manufacturer used

to rate the amp is not a realistic scenario. People who install audio systems don't

have variacs on each power amplifier to hold the voltage high.


A second test after the variac test would be to measure the amp output without the

variac and factor in typical AC line sag caused by typical home installation wiring

and circuit breakers.


A last test that is interesting is to determine how long the amp can run

at full power before going into protect mode {auto shutoff, fuse blowing, etc}.
 

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Do you have access to testing a PLX3402? I'd like to compare notes
 

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Discussion Starter · #11 ·

Quote:
Originally Posted by thylantyr /forum/post/0


Friendly reminder. lol


.

thylantr, I am surprised! It took you 3 1/2 hours to respond! I knew I could count on you for some tidbits. I haven't even posted my methodology yet and you are telling me where to watch out for the pitfalls. The funny part is that I agree with you on most of them. More to come.


Chuck
 

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We can also refer to binks proamp test as they are revealing. His test methodology is

pretty tight. AP analyzer, loads bigger and meaner than ours. lol ...
http://home.pacbell.net/lordpk/bink/bink.jpg


The biggest revealing issue is the AC line sag test at 20hz, 1% distortion. Notice how

all those amplifiers {except the regulated ones, PFC} had a big drop in power vs.

advertised.


Granted, playing continuous test tones is not a normal thing as people play

music instead {lower duty cycle}, but the test tone

is a good reference vs. random music for amp testing. Make the test more like

apples to apples.


Bink tested at only 4 ohms per channel and he got those results. Many proamps are

rated for 2 ohms per channel, a more difficult load. Imagine how bad many of these

amps would score if a 2 ohm per channel test was done. I have a theory as

to why he didn't do a 2 ohm per channel test, I will be brave and say that the

risk of blow up the amps rises alot if you use a rms test method on these amps at 2 ohms... [because I blew up my amps doing this type of test, lol] ..You

can probably perform a burst test to protect the amp.


It would be nice to correlate EP2500 test results to Binks Tapco J2500 tests

because it's rumored that J2500 is a RMX2450 clone just like EP2500 is a clone

of RMX2450.


Bink has no PLX2402, 3002, or 3402 test, those would be nice to test as you can snag those

amps used now for a good price. I have my own 3402 'clipping' test results.


Crown XLS would be nice to test because version D [new ones] has a new

look inside that might make these amps perform better than older versions [A - C].


Crown XTI is new, but one issue bothers me. Crown said it's class AB, not class H.

Looking at gut pics, this has me concerned about it's advertised power. Running a high

powered amp in class AB mode is just a big generator of heat, hence why high powered

proamps are class H, at least 2 tier. When I tested my PLX3402, I bypass the class H

and force it to operate at class AB 100% of the time. The results were disturbing. The

amp fans at idle operation went into high speed mode as the heatsink got very hot. lol


EP2500, PLX's, XLS's, XTI's, would be a nice addition to add to Binks test. The amp test

list would be sweet.


Anyone going to volunteer their amps for testing - harrr...................


Amp guts pics {many snagged from cyberspace}
http://home.pacbell.net/lordpk/proamps/
 

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Discussion Starter · #13 ·
There will be 2 parts to the testing of amplifiers. The first part involves verifying whether or not the amplifier meets the published specs of the manufacturer or not.

The test equipment will be turned on and allowed to warm up and stabilize for at least 1 hour, if not longer. The DUT will be hooked into the test bench and will run at 1/2 power into an 8 ohm load with both channels driven for at least 1 hour to make sure it has settled in. When possible, I will try and duplicate the published specifications of the unit. For instance, if you read the specification sheet below taken from the Behringer website, most specifications are given as 'X' ohms, 'X' watts at 'X' % distortion. But if you read down to line 15 in the left hand column it reads "DISTORTION
 

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Discussion Starter · #14 ·

Quote:
Originally Posted by thylantyr /forum/post/0


We can also refer to binks proamp test as they are revealing. His test methodology is

pretty tight. AP analyzer, loads bigger and meaner than ours. lol ...


The biggest revealing issue is the AC line sag test at 20hz, 1% distortion. Notice how

all those amplifiers {except the regulated ones, PFC} had a big drop in power vs.

advertised.


Granted, playing continuous test tones is not a normal thing as people play

music instead {lower duty cycle}, but the test tone

is a good reference vs. random music for amp testing. Make the test more like

apples to apples.


Bink tested at only 4 ohms per channel and he got those results. Many proamps are

rated for 2 ohms per channel, a more difficult load. Imagine how bad many of these

amps would score if a 2 ohm per channel test was done. I have a theory as

to why he didn't do a 2 ohm per channel test, I will be brave and say that the

risk of blow up the amps rises alot if you use a rms test method on these amps at 2 ohms... [because I blew up my amps doing this type of test, lol] ..You

can probably perform a burst test to protect the amp.


It would be nice to correlate EP2500 test results to Binks Tapco J2500 tests

because it's rumored that J2500 is a RMX2450 clone just like EP2500 is a clone

of RMX2450.


Bink has no PLX2402, 3002, or 3402 test, those would be nice to test as you can snag those

amps used now for a good price. I have my own 3402 'clipping' test results.


Crown XLS would be nice to test because version D [new ones] has a new

look inside that might make these amps perform better than older versions [A - C].


Crown XTI is new, but one issue bothers me. Crown said it's class AB, not class H.

Looking at gut pics, this has me concerned about it's advertised power. Running a high

powered amp in class AB mode is just a big generator of heat, hence why high powered

proamps are class H, at least 2 tier. When I tested my PLX3402, I bypass the class H

and force it to operate at class AB 100% of the time. The results were disturbing. The

amp fans at idle operation went into high speed mode as the heatsink got very hot. lol


EP2500, PLX's, XLS's, XTI's, would be a nice addition to add to Binks test. The amp test

list would be sweet.


Anyone going to volunteer their amps for testing - harrr...................

I have a Sam Ash right down the street from me and a slush fund for buying and returning amps, so we will see what we can dig up. I might even talk them into loaners for an afternoon on the weekends. I also have a lot of friends that play live for a living and can probably borrow an amp from them during the week. Right now, I have the EP1500, the EP2500, and the Crown K2 for sure so I will get those done and then proceed from there. I fully intend to test with 2 ohm loads. Those loads are not out of line for real world usage for a lot of users. And I am using my amps to start with so if I blow them up I only have myself to blame.


Chuck
 

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Quote:
As far as AC voltage goes, I differ with thylantr. The 1st part of the test will be to published specs. If the specs say 120 VAC, then I will adjust the line to reflect that. In the 2nd part of the test though, I can run the DUT off the outlet (a dedicated 20 amp circuit) and monitor voltage and current without voltage adjustment

Found a one word typo in my post, but this above is what I meant. Test the amp using

your variac, then do a test using your 20A circuit only.


Bonus: Score an Itech for testing
 

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I am excited to hear your results for the EP2500's, I am using a whole lot of those to power some line arrays this summer/fall. I doubt the amp would do much for 2ohm loads below 20Hz, thats why I am using them above 80Hz. Also wondering if it might be possible to do super low impedance testing with high frequencies, I am really curious if it could handle something like a 1 or 2ohm load bridged for my tweeters.
 

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Discussion Starter · #18 ·

Quote:
Originally Posted by armystud0911 /forum/post/0


I am excited to hear your results for the EP2500's, I am using a whole lot of those to power some line arrays this summer/fall. I doubt the amp would do much for 2ohm loads below 20Hz, thats why I am using them above 80Hz. Also wondering if it might be possible to do super low impedance testing with high frequencies, I am really curious if it could handle something like a 1 or 2ohm load bridged for my tweeters.

The first amp I am going to test will be the EP1500. I am doing this amp first to sort of get my methodology down pat and see what works and what doesn't. Since a lot of people own an EP2500, that will be the 2nd amp I am going to test. I am planning on a 2 ohm load test at 10 Hz and I can probably add a 2 ohm bridged in the 10K to 20K range if you want.
 

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Discussion Starter · #20 ·

Quote:
Originally Posted by Scott Simonian /forum/post/0


Can't wait to hear the results on the 2500, myself.


How's the progress on that sub EQ going if I may ask, Chuck?

The SUB EQ project has been sidetracked waiting for the circuit to be approved and transferred to printed circuit board design. I have just been told that the design for screening the boards will be done the last week of June and we should see boards by the end of July if all goes well.
 
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