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How to accurately test headphone amp?

post #1 of 7
9/14/12 at 12:03am
Thread Starter 

Is there a way to test headphones amps short of setting up an oscilloscope at my house?  I downloaded RMAA software and have been playing around with that some.  Just using the Line In on my laptop.  I understand that without a nice sound card I might not be able to accurately compare my results with other more sophisticated set-ups, but I assume I could test different aspects for instance "burn-in", test between two amps. 

 

Is it fine to do it this way and what are your suggestions?  Do's or Dont's?

 

For instance is it safe to directly route my amp through the line-in?  How could i set this up for different impedance loads?

 

Are there better freeware programs to use? 

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post #2 of 7
9/14/12 at 12:34am

There is some discussion relevant to this topic here, and you may also want to read the "RightMark Audio Analyzer" article and comments at a certain blog (http://*******.blogspot.com/2011/02/rightmark-audio-analyzer-rmaa.html, I do not post the full link because of forum rules).

You probably do want a decent USB DAC/ADC for your laptop, as the onboard converter is likely to be worse than the amplifier you intend to test if it is a high quality one. "Burn-in" in modern solid state amplifiers normally has extremely minor effects at best, which would be hard to measure, let alone hear. With some minor investment (DMM, test loads, etc.), you could test some basic parameters of the amplifier, like the maximum power, output impedance, frequency response, and if it has significantly higher distortion than your laptop's onboard audio.


Edited by stv014 - 9/14/12 at 12:36am
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post #3 of 7
9/14/12 at 4:25pm
Thread Starter 

Thanks I will read through those two links.  I am sure I will have more questions as things progress. 

 

While I am not sure classic "burn-in" is real beyond some quick mechanical loosening, I have noticed that with my solid state amp after it has been on for a few hrs it sounds a little better to me, better bass response.  I think this might easily be some psychological thing, but would like to investigate, it is the scientist in me.  This sort of test seemed to me to be applicable even with a less than optimal onboard PC soundcard, seeing how that "variable" would remain constant btn tests.

 

I will test some of the other features with my DMM after I read more on how to exactly do it. 

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post #4 of 7
9/15/12 at 7:46am

You may also find the Audio DiffMaker utility useful, it allows for creating a difference signal between two recordings, while ignoring simple level, delay, and frequency response differences.

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post #5 of 7
9/15/12 at 10:52am
Thread Starter 
Quote:
Originally Posted by stv014 View Post

You may also find the Audio DiffMaker utility useful, it allows for creating a difference signal between two recordings, while ignoring simple level, delay, and frequency response differences.

Thanks I will test that to.

 

Just to be clear on something.  Before I plug amp into my Line-In on my PC I need to run it through some parallel resistors to force a voltage drop so that I don't burn up my soundcard?

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post #6 of 7
9/15/12 at 11:05am
Quote:
Originally Posted by icehole View Post

Thanks I will test that to.

 

Just to be clear on something.  Before I plug amp into my Line-In on my PC I need to run it through some parallel resistors to force a voltage drop so that I don't burn up my soundcard?

 

Parallel?

 

Depends on the output level, anyhow.  Yes, you want a voltage divider (two resistors in series with each other, that are in parallel to the load and hopefully higher values than the load) if you're testing output levels higher than the line input can handle.  First step is to check with a voltmeter anyway.

 

Be careful about grounding issues, some amps not liking being connected to a line input, and so on.

 

There are some cheap sound cards and interfaces you could use with a laptop, that should be quite a bit better than the integrated input on most laptops.  You might want to run the laptop off of battery power for tests.

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post #7 of 7
9/15/12 at 11:50am
Thread Starter 
Quote:
Originally Posted by mikeaj View Post

 

Parallel?

 

Depends on the output level, anyhow.  Yes, you want a voltage divider (two resistors in series with each other, that are in parallel to the load and hopefully higher values than the load) if you're testing output levels higher than the line input can handle.  First step is to check with a voltmeter anyway.

 

Be careful about grounding issues, some amps not liking being connected to a line input, and so on.

 

There are some cheap sound cards and interfaces you could use with a laptop, that should be quite a bit better than the integrated input on most laptops.  You might want to run the laptop off of battery power for tests.

Opps yeah, series for voltage divider.

 

Thanks for the information.  I will check output with voltmeter first. 

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