Measuring Amplifiers - Page 14

Here are the 8 ohm and 4 ohm bridged mono measurements.

This puts out quite a bit of power.... but getting it to do it at a steady state was another matter. Since this amplifier belongs to WillD, I did not feel that I had the right to take it apart and burn it up. He might get upset. But with steady state 4 and 8 ohm bridged mono, I could hear the amp trying to do it and only really being limited by the circuit breaker in the amplifier. It would have run and run at temperature just fine with a bigger breaker. No, it would not do it for 4 hours straight, but I bet it would do it for 10 minutes or so. That is pretty impressive for a modern day amp.

Chuck

Here is what this amplifier looks like.
Left front -


Right front -


Center Indicators -


Left rear -


Right rear -

You are close. If an amplifier says it can do 100 watts at 8 ohms at .1% THD, then you can hook it up to an 8 ohm load bank and raise the level until it reaches 100 watts, then read distortion, or raise the level until it reaches
.1%, then read wattage. This works well when you have a well behaved, low wattage unit. Fast forward to 2007 with class H behemoths that are not meant to put out constant power for any given amount of time. AT most you get much less than 30 seconds of measuring time at full power to check distortion or vice versa before the unit self destructs and protection systems kick in or the amp smokes. These amps should be checked with a burst cycle that will automatically raise the power level into the stratosphere and then lower the power back into A/AB range where it will do steady state sine wave. It is very easy to see any change in the waveform at all in a class H amplifier. Most of the time instead of clipping some form of oscillation will appear on the waveform. When they do clip (it is very apparent) they do not 'hard' clip by cutting the tops and bottoms off of the waveform, but they distort the waveform.

Most of these amps I am testing are made to be used in a professional sound system environment where they should work when you turn them on 24/7 and they should be lighter weight for travel purposes. It would then make sense that to be able to double the power of an amp, you would have to carry half as many of them in a truck, thereby saving fuel costs.

These amps were not meant to find their way into the living rooms of American Home Theaters. If you were to judge this amplifier against a boutique audiphile amplifier that cost $5,000 or more, the boutique amp would put out its rated power all day long into a load and have unmeasurable distortion. There would be no forced air cooling in the boutique amp. But the boutique amp would not put out the massive watts needed by the subs we use. Pro amps do not have to have the pedigree for S/N and distortion that home amps can have. That being said, the pro amps being built today are so much better, quieter, powerful, and robust that there is no comparison.

Think about carrying 200 Crown DC300A amps at 4 rack spaces high and 150 watts per channel versus an XS900. No comparison.

I was asked by a guy who's name starts with W and ends with D to check the frequency response of the XS900 to see what it down in the lower regions.
Here it is:
100 Hz - 0.00 db
020 Hz - 0.00 db
015 Hz - 0.00 db
12.5 Hz - -0.10 db
010 Hz - -0.20 db
009 Hz - -0.40 db
008 Hz - -0.50 db
007 Hz - -0.80 db
006 Hz - -1.50 db
005 Hz - -2.3 Hz
004 Hz - WILL NOT REPRODUCE!

At any frequency under 5 Hz the amplifier will not reproduce that frequency. It appears to be a protection factor. At 5 Hz, the amp acts normal, at 4 Hz, it starts the fans whirring and then turns the signal off. Move it back to 5 Hz, everything returns to normal.

Chuck