Measuring Amplifiers - Page 2

Here is the 2nd round of measurements completed at 4 ohms. Again, the high frequency is not up to par.

Just a note..... After finishing the measurements at 4 ohms, I used a non contact infra red thermometer to measure the temperature on the case where the heat sink is bolted to the cover. The thermometer was reading between 110 degrees and 115 degrees. This is with an unmodified fan system, BTW.

Phil:
There is no 'arbitrary' limit. It is based upon published manufacturers specifications. I consider the amp out of bounds when it will not meet the manufacturers specification. In this case the EP1500 should be able to do 260 watts into an 8 ohm load with less than .1% THD from 20 Hz to 20 KHz. I could make the amp do 260 watts at 20 KHz with outrageous unlistenable distortion or I could run the amp at .1% THD and measure the watts
As far as running a high/max wattage on amps, I have tried it on the EP1500 and it is barely worth noting. This unit barely meets factory specs much less outperforms the specs. I am sure on units like a QSC or a Crown you will see performance above and beyond the published specs.

If I had the time, I would 'play' with the amps all day long. As it is, it has taken me since 10 AM this morning to get 2 sets of measurements. Thats 6 hours. For an amp like the EP1500 I wil not go much farther than checking it for meeting specs. You can tell when you are setting up and testing if an amp is worth investigating any further and this one is not. I will probably go deeper with the EP2500 and the Crown K2 when I test them.

Chuck

Just an update.............. I am in the process of testing at a 2 ohm load, both channels driven, at 1 KHz. In 20 minutes of test time, I have blown the dedicated 20 amp breaker 5 times attempting to get the amp up to clipping and just take a reading of voltage and distortion. In that time the case of the amp has registered 125 degrees fahrenheit on the top cover. So far it will only do approx 500 watts at .5% distortion. I am going to let it cool for a few hours and rerun the test to see if it will meet specs. Very disappointing so far.

It is on the menu. Have patience. I am still letting the amp cool down from the 2 ohm attempted test. After I get the 2 ohm results, i will get some bridged results.

OK, here is the 2 ohm testing results for the EP1500 amplifier. I only did one test at 1 KHz full power, both channels driven. Behringer specifies that this unit will do 700 watts RMS at 0.1% THD both channels driven. I could not get the amp to go past 35 volts per channel before it would blow the circuit breaker on the amp itself. Here is the report. For the record, the amplifier is drawing 16.4 amps from the outlet at this power level. (BTW, the manual states that it will draw 6.7 amps at 120 VAC, the circuit breaker supplied on the amp is 15 amps!).



It took less than 30 seconds for the amp to go from 70 degrees fahrenheit to 110 degrees when under power. After the amp cools down, I wil perform some bridged mono tests.

All the tests I am doing will be in this format being presented so that you can compare apples to apples. Same frequencies, same loads, same methodology. One thing to realize is that to put the amps on the bench with a static load and a pure sine wave at high voltage and let them cook is far more punishment than they wil ever see when playing music in our homes. OTOH, the manufacturers publish the specifications that say what theses pieces of equipment are capable of.

If you want to send a Buttkicker, PM me and we can work out details. I will gladly put it on the bench and test it.

All AC voltage is 120 VAC as output by the variac. It has taken me 10 hours to get this far on 1 amp. I will have to investigate what it takes to add a '96 VAC' portion to the test. I will look at Bink's testing again so I can see what is common between our tests. Since this is my first test it is easier for me to change to follow Bink now than later down the road.

And actually, many proamps don't even care about running 20 Hz for an extended period of time with pure sine waves if they are designed well. Crown DCA, Yamaha P series, Crest, QSC, etc. I even remember a Phase Linear 700 able to passs 20 KHz without a sweat for an hour at a time!

Here is the final test of the EP1500. I have tested both 8 & 4 ohms bridged mono. The 8 ohm test went well but the 4 ohm test did not fare too well even at 1 KHz so I did not even go any further with it. The circuit breaker on the amp kept blowing just as I would aproach ful power in 4 ohm bridge mono. Note the increased distortion at 4 ohms also.



Ok, that is it for the first amplifier in my tests. If you have comments, gripes, suggestions, or preferences for a format let me know now or forever hold your peace (yeah, right, on AVS ). I am going to try and fashion some tests to fit with Binks spreadsheet but that may be down the road.

Chuck

For those that have not seen it, here are Bink's tests.

No, no weighting curves are being used, but a 30 KHz LO PASS filter has been engaged for all tests. I did put an A weighting filter in this morning and checked the distortion. It dropped to .0002% at 20 KHz. Not very realistic. If you want to learn more about the quandry of amplifier measurement, especially as it applies to pro units, then read this article.

http://www.soundandcommunications.co...6_06_audio.htm

Here are the 8 ohm results for the EP2500 amplifier rated at 450 watts/channel 20-20KHz at <0.1%THD both channels driven.



If you are wondering how much more power this amplifier will give up before shutting down, it won't! This is the ragged edge for this amp. It will either go into oscillation or shutdown from thermals before giving more power.

Here are the 4 ohm results for the EP2500 amplifier rated at 650 watts/channel 20-20KHz at <0.1%THD both channels driven.



Some interesting notes. The digital ammeter connected to the amplifier registered 17.2 amps at full power 1 KHz. The thermometer registered 158 degrees fahrenheit on the top case of the cover where it is attached to the heat sink. It was cookin'.

Chuck