How do you compare 2 headphone amps?

Hi everybody,
 
I'm new here (sorry for my English), so please forgive me if it has already been discussed here... (and I hope I'm posting in the right section..)
I'm curious about how you compare 2 headphone amps in order to tell if you prefer A or B ...
I know that the levels must be the same on both amps, but I find that unplugging/plugging the headphone is very distracting and I find it difficult to objectively compare 2 amps.
 
Can you please share how you make your own comparisons?
 
Thanks in advance

It would be really hard to measure two amps objectively just by ear. All of the objective testing is done with equipment while matching the volume pot via dB using a measuring device. For A and B testing with just yourself, it would be more on the subjective side. Regardless of how unbias you want to be. Good luck. 

You can use a pre-amp with two sets of outputs to play the same music at the same output level on two headphone amps at the same time. If you have two of the same headphones you don't have to do any unplugging.

Here are my personal experiences... Of course YMMV.
 
First and foremost it has to be done "blind".  Blindfolded, eyes closed, back to the rig...etc.  So I always need the help of someone else (another head-fier) to plug and unplug without me knowing what I am listening too.
 
Secondly the listening environment needs to be completely silent for critical listening sessions.  So unfortunately this negates most of the larger convention hall venue head-fi meets.  Unless of course you are using IEMs.
 
Yes volume levels need to be equal.  Louder sounds will naturally sound more dynamic.  Really loud sounds (concert level) will sound more compressed.  On top of that, the equipment+headphones will exhibit different levels of harmonic distortions, and introduce other "signature" resonant overtones-undertones at different output levels.  It ALWAYS makes me nervous hot-plugging TRS connectors, so out of respect to others' equipment (any my own too!!) I ALWAYS plug/unplug with the volume at 0%.  Unfortunately by the time I have my head-fi buddy "re-normalize" listening volume, my brain to some degree, has re-acclimated and adjusted to the signature of rig or piece of gear I am comparing.
 
I also need to play the same exact music passage/tune. Again, almost impossible to do without the help of a buddy... unfortunately.

^ all true, but I'd add that there is a difference between blind a/b testing and comparing - sort of like critical listening and enjoying music.

parbaked said:

  ^ all true, but I'd add that there is a difference between blind a/b testing and comparing - sort of like critical listening and enjoying music.

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Absolutely... the OP uses the words "objectively compare".  That phrase in itself opens up a degree of subjective interpretation.  I took it to mean "without influence of ones eyes".  Hence my views/opinions on a blind A-B.

kramer5150 said:

  Absolutely... the OP uses the words "objectively compare".  That phrase in itself opens up a degree of subjective interpretation.  I took it to mean "without influence of ones eyes".  Hence my views/opinions on a blind A-B.

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Yes, but the OP is mrmagoo. All his testing is pretty much blind...
 

Side note... tube rolling is even harder because they (ideally) have to warm up and cool down every time.  That can be a ~10 minute turn around depending on the tube and amp.

Thank you all for your inputs,
 
[to parbaked: hahaha, no, I'm not as blind as the real Mr Magoo...]
 
In fact what I would like to do is choose the amp that I prefer between 2, which means for me that ideally I can swap from one to another and perceive immediately what difference there is regarding soundstage, bass... so I can say without any doubt "I prefer amp X". I agree with kramer5150 that it's better to do it in a blind test without knowing which one I'm listening to.
Some time ago I tried with a friend to make a comparison using his HD600 from the output jack on the front panel of his CD player (marantz) and using a 3 channel beta22 that he built, and honestly I couldn't find any (obvious) difference in the sound quality. But the time that it's necessary to unplug/plug and increase the volume again, as we swapped from one to another (he too reduced the volume to zero before unplugging !) makes it difficult to trust our own memory and do a reliable comparison.
If there was a way to swap instantly from one to another without stopping listening, that would be just perfect...

I have also read that some people write notes after listening to A, and then listen to the same track with B, and write some notes and then compare the notes. But for me personnally I'm not able to do that because I'm not able to describe what I hear and put it into words... and I'm not convinced it's a very reliable comparison method...

That doesnt surprise me vintage marantz receivers have long been known to have very good sounding headphone outputs.

Sometimes ill jot down notes when listening... Not always though.

kramer5150 said:

Side note... tube rolling is even harder because they (ideally) have to warm up and cool down every time.  That can be a ~10 minute turn around depending on the tube and amp.

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That's the reason I am going to stick to solid state amps. I drove myself crazy with my guitar tube amps swapping tubes!

Hi,
I made some research, and maybe found something that should work for what I want : do you guys think that this is what I need? http://www.head-fi.org/t/662441/fiio-headphone-signal-switcher-hs2-open-to-retail-now

mrmagoo said:

  Hi,
I made some research, and maybe found something that should work for what I want : do you guys think that this is what I need? http://www.head-fi.org/t/662441/fiio-headphone-signal-switcher-hs2-open-to-retail-now

Click to expand...

 
That would be useful. It's no longer being sold in the US, but it seems to be available from vendors in India and Hong Kong. You might also try the device mentioned here: http://www.head-fi.org/t/659603/introduction-about-hs2-headphone-signal-switcher/105#post_10262837.

jonbernard said:

   
That would be useful. It's no longer being sold in the US, but it seems to be available from vendors in India and Hong Kong. You might also try the device mentioned here: http://www.head-fi.org/t/659603/introduction-about-hs2-headphone-signal-switcher/105#post_10262837.

Click to expand...

Hi, thanks for the link, it seems very interesting and the price is very good because it seems to include shipping, but it also seems that no one has used it and commented yet so we can't know for sure if it is good quality... and I would also prefer if it had 1/4" jacks. But for the price it's probably worth a try..
If there is no other solution, I think I will buy one..
I would prefer the Fiio (and it has a 1/4" for the hp jack), but unfortunately, it has a shipping cost nearly as expensive as the device! (I'm in Europe).