Measuring Amplifiers - Page 56

Here is the basic S/N, Frequency Response, and 8 ohm power tests.



And here are the 4 ohm power tests.


You will notice that I was only testing at 1% THD levels. That is because without sophisticated filters any THD levels that I measured at .1% were very obviously just not true and were unduly influenced by the lack of test equipment. (When I would set the THD at .1%, power dropped so low it was just not true.)

With all that being said, I did try this amp in several of my systems at different operating points, i.e. sub amp, mid amp, full range amp. There is a lot more to it than the numbers reveal.

Chuck

This is where it gets more into the subjective a s opposed to the measuring of numbers that are straightforward. What follows are my opinions and impressions and should possibly be taken as the ravings of a lunatic fool!

I tried the IPR-1600 as a subwoofer amp in my dedicated 2 channel system that usually has a QSC PLX3402 driving a pair of sealed 15 inch subs which also have a Marchand Bassis being used to tune them. This is only 2 channel, not home theater so no WOTW bass stuff. Nobody could tell any difference whatsoever when the Peavey was being used vs. the QSC except when it ran out of power. Had I used one of the bigger Peavey amps, nobody would have been able to tell the difference at all between the 2 amps. My subs are crossed at 40 Hz and I am playing High Resolution (upwards of 44.1/16 KHz) music through this system. And yes, there are a lot of pieces with stunningly low bass that sound wonderful in hi res 2 channel music.

I used the amplifer for a while in my bedroom system that uses a pair of Dayton 3 way floorstanding speakers with dual 8 inch woofers, 5 1/2" mid, and Seas H1212 tweeters. Over the years I have used many different amps in the bedroom (usually cast offs from the main system) such as Onkyo receivers, Bryston 3B-ST, Hafler DH-220 modified, and currently a Harmon Kardon AV receiver. I heard a much cleaner upper mid range/high range than I have heard with any other of the mentioned units. I find it very hard to admit that the Peavey IPR-1600 sounded really good as a full range amplifier because my own built in prejudices formed over many years of using pro gear and home audio gear still tell me quite loudly that "PEAVEY IS NOT A HIGH FIDELITY AMPLIFIER". But my ears told me that I could hear more detail that was cleaner and more open than the other amplifiers. It has been quite hard to get over built in prejudices vs. what I heard.

OTOH, when I used the IPR-1600 in my system and pulled out my Pass amplifiers and inserted the Peavey, there was a difference between the two. The Pass amplifiers sounded much better in all areas. This was a comparison of a $3,000+ amplifer vs. a $300 amplifier. That being said, there was not a 10X difference between the two. Law of diminishing returns. And my class A Pass amps double as space heaters also

The amplifier sounds better than the numbers reveal, even the factory specs. If I had to criticize this amplifier, it would be external to it. GET RID OF THE BLUE LED's!!!! (marketing's fault) The thing lights up like a roadhouse in the middle of the night on a lonely southern road. Where are the binding posts? (a cost cutting measure). The fan in the amplifer is just too damn loud for the unit to sit in the same room. All of these criticisms are a moot point as soon as you use the amplifier for it intended purpose. Pro Sound Amplification. If you can work around these points, you have a damn good $300 amp that will play good high fidelity music.

Chuck

Yes, actually it is because of the way the amplifier works. There is a lot of high frequency in this amplifier (when I say high frequency, I mean much higher than 100 KHz). Part of my problem in measuring this amplifier is that I was able to use a 30 KHz filter in my HP to cut off some of the high frequency and try to just measure the fundamental, but it also allows the non audible harmonics to come through and be measured as THD+N at the lower frequencies. When measuring 20 KHz with a 30 KHz filter I was able to get "more" perceived fundamental than harmonics out of the amplifier so more voltage. Had I been able to switch the filter as I switched the fundamental, you would have seen a smoother response. I questioned JD and the factory about this and they confirmed what I saw on my scope. They use a very sophisticated active filter for their measurements.

Chuck

It doesn't really correlate to 'real full range usage' because it is an effect of my older test gear measuring this particuar piece of equipment. If I had the burst testing Audio Precisoin test gear with the active filter, this would not have shown up as much as it did. What you might find interesting is that the 8 ohm tests showed the 20 KHz measurement as higher than 20 Hz & 1 KHz measurement. But we are only talking about 1 to 2 volts. In the 4 ohm measurements there was a 2.5 volt swing in the other direction.

I could probably have come up with 10 different sets of figures on a single day and maybe showed a trend, but it is hard to say using 'hook up a load, steady state sine wave testing' method as opposed to computer controlled bursting.

To me it is a conundrum. Should the way you test a piece of equipment to get specifications matter? If Peavey chose to manufacture this amplifier and present its specifications using numbers obtained from steady state sine wave testing, would not as good a specification do the amp justice and then the amp would look unfavorable compared to the competition that did not use that method. And now you are back at the beginning wondering why or if there can ever be a common standard for measuring amplifiers? Wait till the next generation of technology is developed and the bursting method in current use does not apply, what next? How will you measure the wattage of a true digital amplifier that only puts out zero's and one's instead of analog waveforms but claims to have 100 watts per channel?

Sorry for the long windedness (sp).

Chuck

I never felt them get warm at all. As a matter of fact the fan would kick in very quickly when running a sine wave into a load and keep them cool.

Chuck