[a44100Hz]

Our brain is a processing center that automatically makes corrections for us when we are listening, such as with volume matching between your ears or spatial imaging. Sometimes new headphones sound bad the first time you try them because your brain is tuned for your old set. Ignoring the brain as a significant component of our hearing seems silly. As far as I know rapid A/B testing allows you to discern changes in frequency response but not much else; your brain needs time to adapt. For me that process sometimes takes days. But try it for yourself. Listening to the same album start to finish, changing equipment, and listening start to finish again should make the full suite of differences between equipment presentation more apparent than fast toggle A/B switching.

 

[gregorio]

Our brain is a processing center that automatically makes corrections for us when we are listening, ...

 
That's apparently not true for some audiophiles who according to them, have two ears which tell them the absolute truth and no brain!!

 
G

 

[watchnerd]

As far as I know rapid A/B testing allows you to discern changes in frequency response but not much else; your brain needs time to adapt. For me that process sometimes takes days. 

 
Other than frequency response, what else are you hoping to hear?
 
Phase? Distortion?

 

[a44100Hz]

Other than frequency response, what else are you hoping to hear?

Phase? Distortion?

It definitely takes my brain some time to re-adjust for things like presentation perspective or soundstage imaging, PRAT, an overall sense of immersion and becoming lost in the music rather than being aware I'm listening to a recording on headphones. The first time I put on an HD650, same system, it sounded nothing like it does now -- it sounded boring, dull. Now it sounds lush, ethereal. Did the technology change? No, but my end processor did.

Similarly, I have a pair of headphones with a channel volume imbalance. Over time my brain compensates for me and I forget about the imbalance and hear them as centered. If I change to matched headphones, the matched headphones sound skewed for a while.

 

[cjl]

   
Other than frequency response, what else are you hoping to hear?
 
Phase? Distortion?

To be fair, distortion is an important factor. However, it's by far the most detectable when testing via fast-switch A/B. Levels of distortion that are inaudible if just listened to in isolation can be detected if you have the contrast of an A/B. You can experiment on yourself here: http://www.klippel.de/listeningtest/lt/

 

[watchnerd]

It definitely takes my brain some time to re-adjust for things like presentation perspective or soundstage imaging, PRAT, an overall sense of immersion and becoming lost in the music rather than being aware I'm listening to a recording on headphones. The first time I put on an HD650, same system, it sounded nothing like it does now -- it sounded boring, dull. Now it sounds lush, ethereal. Did the technology change? No, but my end processor did.

Similarly, I have a pair of headphones with a channel volume imbalance. Over time my brain compensates for me and I forget about the imbalance and hear them as centered. If I change to matched headphones, the matched headphones sound skewed for a while.

 
The easiest way to adapt your brain processor more quickly is with mind altering substances.
 
With enough practice you'll eventually be able to do it sober.

 

[dcd564]

The easiest way to adapt your brain processor more quickly is with mind altering substances.

With enough practice you'll eventually be able to do it sober.

Ha!!! And quote of the night goes to... watchnerd!

 

[asymcon]

To the OP question, an amp should be added to a setup where the source used doesn't have adequate voltage swing, current driving capabilities or high output impedance for a specific set of headphones at given volume. Ideally, an amp, just like source gear should be transparent, e.g. "wire with gain" without any sort of coloration. When one strives for coloration, there are DSP designed for that, but an amp should always be as neutral as possible. 
 
Real world example:
Sansa Clip+ with VE Monks+ (64Ohm) = no amp necessary, Clip+ provides 15mW into 32Ohm load, has 1Ohm output impedance and enough voltage/current driving capabilities for 64Ohm/112dBm headphones. 
 
Sansa Clip+ with AKG K240DF = amp is useful, while Clip+ has enough current drive capabilities, its voltage caps at 0.82Vrms, which may or may not be enough for 600Ohm/88dBm headphones. Therefore an amp provides extra voltage (volume) headroom for high impedance/low sensitivity headphones.
 
Sansa Clip+ with AKG K701 = amp is useful, Clip+ has adequate voltage capabilities for this 55Ohm/91dBm pair, but may start to distort as current limit kicks in. So an amp may act as a buffer and provide K701 with enough current to cover even the highest peaks in volume.
 
As for myself, I'd recommend an O2. You can get one finished, or you can opt in for a little DIY exercise and build one on your own. Price varies between $69 - $129 for the one JDSLabs make. O2 perfectly fits the bill for truly neutral amp with enough potential to drive almost anything close to damaging levels.
 
PS: I consider 100dB peak as "enough". Some may prefer 105dB or 110dB peak. 

 

[dcd564]

  To the OP question, an amp should be added to a setup where the source used doesn't have adequate voltage swing, current driving capabilities or high output impedance for a specific set of headphones at given volume. Ideally, an amp, just like source gear should be transparent, e.g. "wire with gain" without any sort of coloration. When one strives for coloration, there are DSP designed for that, but an amp should always be as neutral as possible. 
 
Real world example:
Sansa Clip+ with VE Monks+ (64Ohm) = no amp necessary, Clip+ provides 15mW into 32Ohm load, has 1Ohm output impedance and enough voltage/current driving capabilities for 64Ohm/112dBm headphones. 
 
Sansa Clip+ with AKG K240DF = amp is useful, while Clip+ has enough current drive capabilities, its voltage caps at 0.82Vrms, which may or may not be enough for 600Ohm/88dBm headphones. Therefore an amp provides extra voltage (volume) headroom for high impedance/low sensitivity headphones.
 
Sansa Clip+ with AKG K701 = amp is useful, Clip+ has adequate voltage capabilities for this 55Ohm/91dBm pair, but may start to distort as current limit kicks in. So an amp may act as a buffer and provide K701 with enough current to cover even the highest peaks in volume.
 
As for myself, I'd recommend an O2. You can get one finished, or you can opt in for a little DIY exercise and build one on your own. Price varies between $69 - $129 for the one JDSLabs make. O2 perfectly fits the bill for truly neutral amp with enough potential to drive almost anything close to damaging levels.
 
PS: I consider 100dB peak as "enough". Some may prefer 105dB or 110dB peak. 

Wow.  This is extremely helpful.  I was a little aware of the O2, but never considered it due to it being an amp only and not a DAC.  In your opinion, would the O2 amp be more than sufficient, and I should just rely on the DAC from my Retina MacBook Pro or any future computer?  Again, awesome feedback.

 

[watchnerd]

 
Wow.  This is extremely helpful.  I was a little aware of the O2, but never considered it due to it being an amp only and not a DAC.  In your opinion, would the O2 amp be more than sufficient, and I should just rely on the DAC from my Retina MacBook Pro or any future computer?  Again, awesome feedback.

 
What year is your MacBook Pro?
 
Recent Macs have excellent measured jitter performance for the S/PDIF output.
 
Coupled with a suitable outboard amp, if needed for headphones that are harder to drive, it's hard to argue that one really needs more.
 
Also, take a look at the Fulla 2.  I prefer it to the ODAC/O2 for ergonomic reasons, and it's both an amp and DAC so if you need to bypass the DAC of some source that is kind of crappy, it can do that, too.

 

[asymcon]

As for one-size-fits-all, IMHO CEntrance DACPort Slim is the best semi-portable solution for both laptops and smartphones. 

 

[dcd564]

What year is your MacBook Pro?

Recent Macs have excellent measured jitter performance for the S/PDIF output.

Coupled with a suitable outboard amp, if needed for headphones that are harder to drive, it's hard to argue that one really needs more.

Also, take a look at the Fulla 2.  I prefer it to the ODAC/O2 for ergonomic reasons, and it's both an amp and DAC so if you need to bypass the DAC of some source that is kind of crappy, it can do that, too.

2014 Retina MacBook Pro. Ha... the Schiit Fulla 2 is what I was I initially contemplating. I wasn't sure if it was powerful enough for the 400i. Some people say planar headphones need at least 1 watt of power to "get the most of out it." Im not sure why if you know the specs and it seems they should match up with the numbers of a particular amp. That's what made me think of the Magni/Modi stack. The bad thing is it's not as portable, and may be an unnecessary upgrade. Then there is the can't mis NFB-11. If money was no object, that would be safe bet. Could it be overkill? Yes, but at least I know it would a good investment. But money is an issue and it also may have no audible differences between it and the Fulla 2 for the 400i.

So, you think the Fulla 2 would be more than enough to drive the 400i without distorting?

As for one-size-fits-all, IMHO CEntrance DACPort Slim is the best semi-portable solution for both laptops and smartphones. 

Thanks for the recommendation. That thing looks pretty sick! It looks like it's not available for purchase right now.

 

[watchnerd]

Schiit Fulla 2 is what I was I initially contemplating. I wasn't sure if it was powerful enough for the 400i. Some people say planar headphones need at least 1 watt of power to "get the most of out it." Im not sure why if you know the specs and it seems they should match up with the numbers of a particular amp. 

 

 
I have both.  Haven't tried them together yet, will do so this weekend.

 

[dcd564]

I have both.  Haven't tried them together yet, will do so this weekend.

Oh man, I didn't even know it was you who replied! I was on my way to teach my next class and was just trying to respond. I apologize, I didn't mean to pressure you to test them/give me an answer right away. I appreciate you listening to them this weekend and giving me your impressions later. Looking forward to it!

 

[watchnerd]

Oh man, I didn't even know it was you who replied! I was on my way to teach my next class and was just trying to respond. I apologize, I didn't mean to pressure you to test them/give me an answer right away. I appreciate you listening to them this weekend and giving me your impressions later. Looking forward to it!

 
No worries!