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Measuring Amplifiers

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#21 ·
Hi Chuck,

About 5 weeks ago I talked to you about coming over to your house with some of my amps. I want to see how your test results will compare with mine. My amplifiers have been through some pretty severe physical abuse when they were out on loan. They didn't sound that bad when they came back, but I'm still interested in seeing bench tests. I'm really more interested in the performance at 1W and 100 mW because that's where the amplifier spends most of its time in a control room or a HT if it's not driving a passive subwoofer. I also want to see you test your other amplifiers to see if I can get the same results with more modest test gear. Let me know when it's a good time to meet.
 
#22 ·

Quote:
Originally Posted by chasw98 /forum/post/0


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.
Click to expand...

2ohms bridged at 10Khz would be absolutely perfect!


I am afraid the EP2500 won't be able to do much for bass, I wouldn't be surprised if it only did half spec or even less, but even still, it is a good value.
 
Discussion starter · #23 ·
Yuriv:

Not this weekend, but the one after will probably be a good time if you want to bring some gear by. PM me.


armystud:

Obviously, I have been running some preliminary tests and have an idea how these amps will perform. You might be very surprised! Should have the EP1500 done before Friday.


You know what they say, the first one takes forever, the rest are easy, I think.
 
#24 ·
any new news?
 
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Discussion starter · #25 ·
Got real busy this week. I will have my first testing done tomorrow for sure.

Hopefully it will get posted in a readable form!
Image


Chuck
 
Discussion starter · #29 ·
Here are the results of the first round of measurements of a Behringer EP1500 at 8 ohms. I have found that I must let the load bank cool down and stabilize betweeen each frequency check, so it has taken approx. 3 hours to do the first round at 8 ohms. I will plod along and get the measurements done for 4 ohms & 2 ohms as the day goes on. Here is a chart of the first round.

Image



You will notice that at 20 KHz the distortion is out of bounds. In order to get the distortion down to a reasonable level, I had to drop the voltage to 43.7 volts which equates out to 225.4 watts at this frequency. Then the distortion dropped to .057 (L) and .042 (R). I was not sure whether this was the fault of the amp or my test rig or what so I spent a lot of time checking and I have no problem measuring .000X% THD at well above 20 KHz and I pulled out my 2nd EP1500 and it displayed the same behavior as the first. I do not believe that this amplifier likes to be tested with a 20 KHz sine wave, even for a short period of time.


I have attached the PDF of this chart for those that wish to save it or print it.

Chuck

 

EP1500-8ohm-060907.pdf 65.0849609375k . file
 

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Discussion starter · #32 ·
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.
 
#35 ·
Hi Chas,

When you find an amplifier that tests "out of bounds" for THD as you've indicated the EP1500 did, is it possible to find out at what frequency the distortion level starts to rise? Would that take up too much time?

Have you set an arbitrary limit as to what level of THD distortion you consider to be "out of bounds" and what is that limit?

Is there a way to run a high/max wattage (sweep) to test for THD levels?

The project you have started will be of very valuable interest to a lot of DIYers AND professionals.

Thank you for your time and expertise in assembling and building the test equipment. I will be patient in waiting for future results of your testing.

Phil
 
#36 ·

Quote:
Originally Posted by rlj5242 /forum/post/0


Has anyone used or even heard of Powersoft amps ? The Q4004 (4x1000 @ 4 ohms) goes for about $550 plus shipping from Germany on Ebay. I've looked for some US retailers but couldn't find them.


-Robert
Click to expand...

Definitley. Mark Seaton would know more, as he's had some hands on experience with the Powersoft DIGAM K10.


And how much is shipping?
 
Discussion starter · #38 ·

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


Hi Chas,

When you find an amplifier that tests "out of bounds" for THD as you've indicated the EP1500 did, is it possible to find out at what frequency the distortion level starts to rise? Would that take up too much time?

Have you set an arbitrary limit as to what level of THD distortion you consider to be "out of bounds" and what is that limit?

Is there a way to run a high/max wattage (sweep) to test for THD levels?

The project you have started will be of very valuable interest to a lot of DIYers AND professionals.

Thank you for your time and expertise in assembling and building the test equipment. I will be patient in waiting for future results of your testing.

Phil
Click to expand...

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
 
Discussion starter · #40 ·
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.
 
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