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Measuring Amplifiers - Page 42

post #1231 of 1913
7/18/08 at 5:57pm
What would happen if you measured the output using a constant amplitude note from a musical instrument?
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post #1232 of 1913
7/18/08 at 7:31pm
Quote:
Originally Posted by arande2 View Post

What would happen if you measured the output using a constant amplitude note from a musical instrument?

1: apart from a synth there isn't a musical instrument with a constant amplitude (at least the potential for one) and 2: how would this be any different from using a sinewave or multiple harmonically related sinewaves at once?

Best power measurement system that reflected real life loads was the Powercube that Peter Aczel used. The Audio Critic blog with results is down for maintenance so I can't link directly. The other is Audio Precision and their burst testing. Stereophile does these tests on amps usually.
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post #1233 of 1913
7/18/08 at 7:54pm
Quote:
Originally Posted by armystud0911 View Post

LOL, I love reading those PMPO specs (meaning "Peak Moment Power Output") In other words, someone, somewhere, somehow, got the amp to do what looks like 1000watts to them, before it went up in flames forever. Now that spec is on every box they sell, it has to be about the most useless spec in the history of audio. On the other hand, I generally assume that they can do about 1-3% of the PMPO and do it with under 10% THD. So it might be ok for powering the midrange on my little nieces boom box (she just turned 3).

Funny thing is ...do you think they even got this much output for one nanosecond? It is an estimate,best case in theory. As the lousy parts and design would not permit this in the real world.

The amp would become a blue smoke generator well before the PMPO advertised rating would be reality and so would the trash can quality speakers it drives.
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post #1234 of 1913
7/18/08 at 8:03pm
Quote:
Originally Posted by fbov View Post

I was asking the question because of the great deal of hand wringing when performance falls short - dramatically short in some cases - of published specs.

I guess the question is if I should care? Will you hear a difference when using actual program material between two 1000W amps if one delivers 1000w at 2 ohm resistive and the other only 500w at 2 ohm resistive. Will the actual SPL be different when both are driving reactive loads?

I hear you and I agree with you. While I also appreciate the effort and thorough documentation Chuck has done and continues to do, I don't really believe they are the best representation of real world amp performance. As to why people are quick to shoot down a company or product based on the results of this type of testing, my guess would be because it is easy.
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post #1235 of 1913
7/18/08 at 11:32pm
Chuck,

Have you tried testing amps capable of parallel-bridging in parallel mode to compare it to driving one channel with the same load and also the results with half the load?

Some people might use it for low-impedance applications or just because they like having high-current capability.
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post #1236 of 1913
7/19/08 at 10:53am
Thread Starter 
Here are some pictures of the inside of a Face F1200TS.





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post #1237 of 1913
7/19/08 at 10:54am
Thread Starter 
Here are some more.





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post #1238 of 1913
7/19/08 at 10:55am
Thread Starter 
And the last of them.





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post #1239 of 1913
7/19/08 at 11:26am
One of the caps went POUF!
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post #1240 of 1913
7/19/08 at 12:03pm
Wow, did that thing get the whole top blown off? That amp looks very beefy in side though.
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post #1241 of 1913
7/19/08 at 12:17pm
Quote:
Originally Posted by TheEAR View Post

One of the caps went POUF!

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post #1242 of 1913
7/19/08 at 12:35pm
Very familiar looking inside when comparing to the T.AMP TA2400 MK-X.
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post #1243 of 1913
7/19/08 at 12:48pm
Thylantyr,

The origin of that blown cap should be verified ! May have the markings .... IED Saddamster Edition Mk. 3

The first prize goes to ButtKicka for the smoke generator amp and its extreme low distortion.
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post #1244 of 1913
7/19/08 at 12:57pm
Face amp (Chucks' pic)










Mystery amp #1 (not T.AMP)








Mystery amp #2 (Yes, a different brand than mystery amp #1)






A little bird sent me those last two pics on another forum.




/muah
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post #1245 of 1913
7/19/08 at 1:43pm
Chas, how long do you run sine waves in your tests, and/or what's the standard industry test duration for max sine wave power?

Thanks
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post #1246 of 1913
7/19/08 at 1:47pm
"Will you hear a difference when using actual program material between two 1000W amps if one delivers 1000w at 2 ohm resistive and the other only 500w at 2 ohm resistive. Will the actual SPL be different when both are driving reactive loads?"

Since subs demand the most power, I'll assume low freq are of primary interest and weird high freq oscillations from reactive loads aren't the concern.

Therefore reactive loads make the amps job *easier*, because they raise the impedance above the minimum established by Re.
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post #1247 of 1913
7/19/08 at 1:52pm
When an expensive amp goes POOF is the quality of the POOF better than a clone amp?
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post #1248 of 1913
7/19/08 at 4:07pm
Thread Starter 
Quote:
Originally Posted by noah katz View Post

Chas, how long do you run sine waves in your tests, and/or what's the standard industry test duration for max sine wave power?

Thanks

In todays world it all really depends on the amplifier. I say that because older amplifiers would run all day long with a sine wave at just below clipping. OTOH, the old amplifiers were not capable of the power levels available today. A good solid amplifer will run just below clipping all day with adequate cooling. That being said, there are not too many good, solid, high power amplifiers. Because of the different types of amplifiers (A, AB, H, D, E, F,G, etc.) they are not all meant for long duration sine wave testing. Some will only pass a 20 ms on/ 100 ms off burst test and call it a day. Some people think that is closer to 'real world' testing and is more meaningful. When an amp will run a sine wave for more than 30 seconds or longer, I will usually let it go for 5 minutes and monitor the heat build up on the chassis with a non contact infra red thermometer. You tend to get a feel for when a protection circuit will kick in and turn the amp off. Most amps won't go for more than a minute at full power these days without a protection circuit kicking in, usually thermal.

You also have to look at a big difference between a home amplifier and a pro amplifier. Most home amplifiers use only passive cooling. If they have the capability to put out large amounts of power (over 500 watts), they usually weigh a lot (approaching and over 100 pounds) but will usually run a sine wave all day long. For a sound system operator, this would be ridiculous to haul around because of space limitations, heat, and fuel costs. But a pro amp that is actively cooled, weighs 20 pounds, can be stacked 7 units high in a portable rack and has the capability to run all day at over 1000 watts makes a lot more sense.

When you adapt a pro amp to your home environment and then want it to perform like a home amplifier, you must give some leeway in measuring the specifications. kind of like wanting a sporty model of a Peterbilt.

Chuck
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post #1249 of 1913
7/19/08 at 8:55pm
Very interesting, thanks, Chuck.
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post #1250 of 1913
7/21/08 at 1:22pm
Quote:
Originally Posted by chasw98 View Post

In todays world it all really depends on the amplifier. I say that because older amplifiers would run all day long with a sine wave at just below clipping. OTOH, the old amplifiers were not capable of the power levels available today. A good solid amplifer will run just below clipping all day with adequate cooling.
...
Chuck

This may be the piece I was missing - your experience.

May I assume this isn't the first time you've done this type of testing? Prior results are a powerful validation of a test process, especially if, in the past, the equipment did sustain power output just below clipping for extended periods of time.

Add that to the home vs pro discussion of physical requirements and one can see that this is one time the pro equipment has the performance tradeoffs - sustained output power for lower weight/transportability and active heat dissipation.

As Noah said, very interesting ...

Frank
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post #1251 of 1913
7/21/08 at 3:37pm
Look at this from a different point of view.

Approx same price range:

Any good home amplifier

vs.

Any good pro audio amplifier

///////// Test #1 100w/ch @ 8 ohms //////////
Home amplifier: Runs all day playing back sine waves,
it's laughing at you because this is so easy to do.

Pro amplifier: Runs all day playing back sine waves,
it's laughing at you because this is so easy to do.


///////// Test #2 500w/ch @ 8 ohms //////////
Home amplifier: Sorry Charlie, the comparible amp in that
price range can't do this.


Pro amplifier: Struggles with continous sine waves as the amplifier
runs into thermal protect eventually, but playing back music is
not a big deal running it all day.


Which amplifier is better? //harr//


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post #1252 of 1913
7/21/08 at 6:26pm
Harrr captain

The pro amp is not audiophile approved! It lacks the beauty plate,fancy connectors and ballast with the blue lights and large dancing meter.And a certificate to get two jars of Poupon mustard at half price.

Harrr
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post #1253 of 1913
7/21/08 at 8:01pm
I have never tried out one of my pro-amps for my mains but I just might one of these days.

I have to admit that with the High End amps a lot of the price goes to cosmetics. I have had some great looking amps that just did not sound as good as advertised but came with the High $$$$ price tag.

Case in point is the Earthquake Cinenova amp which I never wanted to try due to the looks. After getting some advice on the sound from Sherv and knowing that Chas and a few others with a good ear like it, I picked one up. It replaced a very well known MCH amp that retails for about $7,500 depending on how it is configured. To say I preferred the Cinenova over the other amp would be putting it lightly and that was with 2 different sets of speakers from Von Schweikert and Aerial.

If you put these 2 amps next to each other in a rack most people would pick the other amp everyday based on it's looks and reputation without listening to either. Could this be the case with some pro amps? hmmmmmmm
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post #1254 of 1913
7/22/08 at 2:44am
EP2500's get poo poo'd all day long because of Behringer's reputation, the loud fan noise, and their fugly chassis. However, once the fan is dealt with (and its an easy operation) the SQ from them is extremely good. I have been impressed 100x over with how good the cheapy EP2500 can sound on mains duty compared to much higher priced offerings.
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post #1255 of 1913
7/22/08 at 12:52pm
Chuck,

Do you have an ETA for the replacement F1200TS?

Larry
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post #1256 of 1913
7/23/08 at 6:06am
Thread Starter 
Quote:
Originally Posted by 04FLHRCI View Post

Chuck,

Do you have an ETA for the replacement F1200TS?

Larry


I received the replacement amplifier on Friday afternoon, July 18, 2008. If you are wondering when I will get the bridged measurements done, that will be by Saturday, I think.

Chuck
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post #1257 of 1913
7/23/08 at 2:35pm
After reading your amp test, I decided to compare my QSC 2502(450w/ch) to my Carver TFM-45(375w/ch) using my main speakers.

Outcome,,,, the QSC has more base and the Carver sounds sort of hollow in comparision..

So now I'm going to replace 3 of my Carver amps.

I'm on a budget and I'm considering the following:

EP2500 $309 450w/ch 8ohms
QSC RMX 1850HD $350 450w/ch 8ohms

would like to get a QSC PLX1804 $569 600w/ch 8ohms
not sure I can swing this one because I need 3 amps..

I have a 5.1 system...

What do you guys think ?

Regards,
Jose
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post #1258 of 1913
7/23/08 at 3:29pm
Jose,

Pull the cover off of the Carver amps. In series with the speaker output is a 1ohm or so power resistor. Jumper a thick wire across this resistor. This will lower the output impedance of the amplifier a lot and improve the sound quality. With most full range speakers the primary effect will be to increase the midbass output.
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post #1259 of 1913
7/23/08 at 4:44pm
Quote:
QSC RMX 1850HD $350 450w/ch 8ohms

Is that shipped? I know the EP2500 is shipped for under $300 so why not just get 3 EP2500s, you wont be disappointed if you like the QSCs already.
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post #1260 of 1913
7/23/08 at 5:21pm
a QSC RMX1850HD is 350 watts per side at 8 ohms not 450 watts and at 350$ please forward the address i want some because they are 500-600 a pop new on flea bay or at my favorite store :-)
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