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Author Topic: How to test amps properly?  (Read 723 times)

Nathan Riddle

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How to test amps properly?
« on: November 09, 2019, 11:36:14 pm »

tl;dr -> Can someone do a simple writeup of the most important features to look at in an amplifier?


So I've always wanted to learn more about testing amps. Then this thread popped up.

When I say learn more, I'm saying I don't want to continue reading about this, I want to put some stuff into motion.
What excites me is that amps don't make noise (much) unless they explode :P
I've wanted to test more speakers, but I don't have an easy close place to take speakers to and blast music.
I have a number of various amps from low-end Behringer to high-end LineaResearch.

Anyone care to walk me through the process?

Materials:
Software: Smaart, REW, RITA.
Interface: RME/UMC404
Hardware: Linear-X
DUT: D50, NU4-6000, RMX2450, XTI-4002, PLD4.5, iTech8k, DNA20K4

Resources:
I know there is CAF
Data-Bass has some good testing methodologies, but they are for subs not amps.

Personally I'm most fond of this style:
http://diy.poweraudio.ro/albums/userpics/10001/BENCH_COMPARISON_TEST.pdf
I can't find/remember the source.
But this method of testing makes sense to me and is easy to read/understand.

Other resources:
https://www.prosoundtraining.com/2010/03/11/big-dummy-load/
http://www.prosoundtraining.com/site/wp-content/uploads/2014/01/L1109_Amped_Up.pdf
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John Roberts {JR}

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Re: How to test amps properly?
« Reply #1 on: November 10, 2019, 10:00:21 am »

I don't know how good your search skills are, or the old forum data here, but Bink did a very extensive amplifier testing "shoot-out" a number of years ago right here.

There was much discussion about difficulties getting objective results.  Hint- it isn't trivial.

JR
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Nathan Riddle

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Re: How to test amps properly?
« Reply #2 on: November 10, 2019, 12:29:08 pm »

I don't know how good your search skills are, or the old forum data here, but Bink did a very extensive amplifier testing "shoot-out" a number of years ago right here.

There was much discussion about difficulties getting objective results.  Hint- it isn't trivial.

JR

Thanks John,

I think this is what you were referring to: http://forums.prosoundweb.com/index.php?topic=70922.0

Finding the actual files and testing procedure is proving to be more difficult.

---

Let's set some parameters.

I don't want to exhaustively test equipment.
I don't want to spend too much money.

I know I'm not at the same level as anyone of these guys or y'all here.
My goal is to do some simple tests that help me grow in my skill and understanding of the equipment we use.
I dream of being mentored by someone like Langston, Bink, JR, et alia.

Just get a little dirt under my fingernails ;)



---

Other resources:
http://forums.prosoundweb.com/index.php?topic=74914.0
http://forums.prosoundweb.com/index.php?topic=90765.0
https://forums.prosoundweb.com/index.php?topic=76266.0
https://forums.prosoundweb.com/index.php?topic=97418.20
http://forums.prosoundweb.com/index.php?topic=73706.30

This guy is amazing... GEQ testing too.
https://web.archive.org/web/20090317091210/http://binkster.net/geq_shootout.shtml
« Last Edit: November 10, 2019, 02:58:35 pm by Nathan Riddle »
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John Roberts {JR}

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Re: How to test amps properly?
« Reply #3 on: November 10, 2019, 01:41:43 pm »

Thanks John,

I think this is what you were referring to: http://forums.prosoundweb.com/index.php?topic=70922.0

Finding the actual files and testing procedure is proving to be more difficult.

---

Let's set some parameters.

I don't want to exhaustively test equipment.
I don't want to spend too much money.

I know I'm not at the same level as anyone of these guys or y'all here.
My goal is to do some simple tests that help me grow in my skill and understanding of the equipment we use.
I dream of being mentored by someone like Langston, Bink,

Just get a little dirt under my fingernails ;)



---

Other resources:
http://forums.prosoundweb.com/index.php?topic=74914.0
http://forums.prosoundweb.com/index.php?topic=90765.0
https://forums.prosoundweb.com/index.php?topic=76266.0
https://forums.prosoundweb.com/index.php?topic=97418.20
http://forums.prosoundweb.com/index.php?topic=73706.30

This guy is amazing... GEQ testing too.
https://web.archive.org/web/20090317091210/http://binkster.net/geq_shootout.shtml
I worked for years as product manager over all power amps for Peavey. It is all too easy to draw incorrect conclusions from flawed testing.

Modern amplifiers are quite good (better than decades ago) so I wouldn't expect to easily find objective differences between them in casual testing that would represent actual real world performance. Bink and others attempted to use rigor and discipline in their old tests.

This has been pretty much beat to death here over the decades.

JR
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

Nathan Riddle

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Re: How to test amps properly?
« Reply #4 on: November 10, 2019, 03:07:09 pm »

I worked for years as product manager over all power amps for Peavey. It is all too easy to draw incorrect conclusions from flawed testing.

Modern amplifiers are quite good (better than decades ago) so I wouldn't expect to easily find objective differences between them in casual testing that would represent actual real world performance. Bink and others attempted to use rigor and discipline in their old tests.

This has been pretty much beat to death here over the decades.

JR

1) I respect you, your experience and what you're saying. Thank you for your help.
2) I am listening to you, but sidelining my request due to a lack of rigor & discipline isn't fair. I want to get started. The intellectual journey is long and full side quests. Help me get the basics?
3) I agree the statements have been made about modern amps ad nauseam. I disagree that it wouldn't be helpful to ME to learn some simple tests that are useful.

Perhaps let me rephrase.

JR, would you kindly tell me the first 3 simple tests you would do if you had two amps on the table and wanted to compare the major differences.
Given the following test equipment: o'scope; dual FFT; and a 1ch 4kw 2ohm load bank; w/ voltage & amp probes rated for 4kw.
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John Roberts {JR}

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Re: How to test amps properly?
« Reply #5 on: November 10, 2019, 03:49:28 pm »

1) I respect you, your experience and what you're saying. Thank you for your help.
2) I am listening to you, but sidelining my request due to a lack of rigor & discipline isn't fair. I want to get started. The intellectual journey is long and full side quests. Help me get the basics?
3) I agree the statements have been made about modern amps ad nauseam. I disagree that it wouldn't be helpful to ME to learn some simple tests that are useful.

Perhaps let me rephrase.

JR, would you kindly tell me the first 3 simple tests you would do if you had two amps on the table and wanted to compare the major differences.
Given the following test equipment: o'scope; dual FFT; and a 1ch 4kw 2ohm load bank; w/ voltage & amp probes rated for 4kw.
I would plug them in and see if they make sound.

As long as modern amps are operated in their linear region (not clipped or over loaded), they should exhibit pretty much the same transfer function (sound the same).

JR 

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Frank Koenig

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Re: How to test amps properly?
« Reply #6 on: November 10, 2019, 07:14:18 pm »

To test modern amplifiers to their full capability you're going to need a way of generating tone bursts. The amps can put out far more power for some tenths of a second than they can continuously, which is just fine for (most) music. If you try to run them to full output into a load for longer than that they'll go into thermal limit, pop breakers, and will undergo a lot of unnecessary stress.

The tone bursts don't need any sort of fancy window function for the envelope, a rectangle will do. Some "function" (sine, triangle, square, pulse) generators have a gate input that can be driven from a separate pulse generator. That's what I use. Alternatively you could use an "arbitrary waveform" generator, or a computer audio interface (sound card) along with some programming to generate sound files with the waveform you need. There are no doubt other ways, too. I suppose you could build a gate using an analog switch, or even a small, fast relay.

If you're just looking for clipping a digital scope will show that. If you want to do detailed distortion measurements you'll need to use a computer audio interface and analyze the recorded waveforms somehow, or an expensive analyzer such as Audio Precision.

For load resistors look for heating elements that have the right resistance. You can submerge them in water to extend their power handling and reduce the increase in resistance as they heat up.

A trick, that I've mentioned before, is to make a high-power voltage divider so that you can run the amp at full tilt boogie while critically listening at a pleasant level.

--Frank

It occurred to me that you could use the gate function in a digital mixer with the side chain coming from a pulse generator to generate tone bursts. Many ways...

Another thought. Don't forget to examine distortion at very low power levels. Some amps might do fine near full output but exhibit a dead-zone or "crossover distortion" (a terrible term) near zero. This might matter more than you think even for live sound. A dynamic program that hits peaks of several 100 W might have quiet parts that are 10s of mW. This was a common problem with old class AB continuous (non-switching) amps, both vacuum tube and semiconductor, if the output stage bias circuit got wonky.  --Frank
« Last Edit: November 10, 2019, 07:34:03 pm by Frank Koenig »
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ProSoundWeb Community

Re: How to test amps properly?
« Reply #6 on: November 10, 2019, 07:14:18 pm »


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