[SunshineReggae]

You should ask yourself why you would expect to hear a difference. There is a very good reason they sound the same. If you read up on amp science, you will understand that it's extremely logical the way these things are turning out for you. It's only audiophiles who believe there is more to the sound who now have you questioning why you don't agree with them. It's also only audiophiles who consider science incapable of explaining the differences in audio quality between amps... Go figure.

 

[Claritas]

Stay in reality - and try EVERY HP unamped (well...externally unamped) first.

That's good advice. It's also good advice to try everything amped too.

 

[Headzone]

If your HD600s have only had 8 hours of play then that explains why they sound similar when plugged into a cheap speaker amplifier. New headphones often sound terrible before they loosen up. Once they cohere after 100 hours and you get used to their sound you will notice a difference if you plug them into your speaker amplifier.

That's BS in my opinion.
 
If they sound bad out of the package, they sound bad. Maybe they are broken!

 

[TheInquisitive1]

That's BS in my opinion.

If they sound bad out of the package, they sound bad. Maybe they are broken!

It's not that they sound 'bad', heck, they sound great! But they sound the exact same level of greatness without the O2...but my £10 Ozone are identical also....I'm thinking it's the FLAC files that are making them good. It's driving me crazy- It just feels different, but sounds the same. I didn't pay £220 for 'new pads'. I just don't understand.

 

[SunshineReggae]

That HD600 sound same as your Ozone is absolutely strange. That is unimaginable.

 

[depleted]

Try get someone blind test you with FLAC and 256/320kbps mp3, I'm guessing you'll not score more than 50%. FLAC difference is harder to hear than amped/unamped. For what it's worth my E10K doesn't make my X2 sound that much different, there is just no background noise and details seem a little more defined, but in a blind test I'm not sure to score well. By the way until 3 weeks ago I was about to buy HD600+O2/ODAC myself..

 

[Headzone]

Well O2 and your computers soundcard probably both measure flat. So they sound "the same". 
 
In fact they don't. With O2 you get much lower distortion and more gain. Listen to some uncompressed music with some peaks, it should become REALLY noticeable. Try playing some (uncompressed) real hard hitting drums for example. Without amp there is not much dynamics and the HD600 will sound like a pair of cheap cans. With O2 the HD600 will sound just as big as the drums were recorded.
 
Another thing amp should affect is bass tightness. Some people claim to hear tighter bass with some amps which is true.
 
Difference with very compressed music and low listening levels is lower. But some people can still hear if amped or not.
 
HD600 is not "awe-inspiring"-can so maybe you're expecting too much. They are very transparent.

 

[Head Injury]

  Well O2 and your computers soundcard probably both measure flat. So they sound "the same". 
 
In fact they don't. With O2 you get much lower distortion and more gain. Listen to some uncompressed music with some peaks, it should become REALLY noticeable. Try playing some (uncompressed) real hard hitting drums for example. Without amp there is not much dynamics and the HD600 will sound like a pair of cheap cans. With O2 the HD600 will sound just as big as the drums were recorded.
 
Another thing amp should affect is bass tightness. Some people claim to hear tighter bass with some amps which is true.

They'll only sound different if one can't swing enough voltage to reproduce peaks without clipping, one's noise and distortion etc. is actually audible, or one's output impedance is very high (this is what might account for less tight bass). Otherwise dynamics should be exactly the same. As we don't know the specs of what else the OP is using, we can only assume these are issues. As he presumably can't hear a difference between his headphones even using the O2, I think the quality of the rest of his gear is the least of his worries right now.

 

[Head1]

There was a guy on youtube who built his own "o2" and found no difference to the iphone.
 
Try different amps and go by what your ears tell you. If possible, get someone to do blind listening tests with. It looks like you might be giving it back anyway but it's better to know rather than being told what they should sound like. 

 

[Posam]

If you really don't think it makes enough of a difference, sell/return the amp. I've been running my Grado RS1i without them for years and I enjoy them plenty fine. I have a small portable amp that didn't add or detract much to my ears and buying an amp for my Grados has just never interested me. 
 
Trust your ears and I'll say to stick with the amp as long as you can before any return period is up so that you don't make a decision too quickly.

 

[Sundown]

My phone ran the HD600's all the way one down from max to an appropiate volume. One click more was max and was too loud for my taste.

 

[StudioSound]

This seems rather unusual. With the HD600's 300ohm impedance they are hard to drive and require a dedicated amplifier to drive them well.

No, high impedance headphones are easy to drive. The only difficulty with them is getting enough volume.
Low impedance headphones are difficult to drive, since they need to be paired with a low impedance amplifier to work well.
As a general rule, amp impedance must be lower than 1/8th the headphone impedance.

300/8 = 37.5 ohm. Something needs to have a really bad headphone output to be greater than 37.5 ohms. Generally this will be older AV Receivers.
16/8 = 2 ohm. Low impedance headphones require a very low output impedance to be properly damped.

The biggest difference I noticed switching to a good amp/dac is that the background noise completely disappears. There is no hiss at any volume or with any headphones connected to my Benchmark DAC2.
With lower impedance headphones like my MDR-7520 (24 ohm) there is more bass, it's less distorted, and much better controlled. The headphones also sound a lot more "dynamic" with good tracks.

https://cdn.shopify.com/s/files/1/0321/7609/files/Headphone_Amplifier_Performance_-_Part_2.pdf


I also agree that if you were happy with things before, and you are not bothered by, or notice what may be more subtle changes to some people, it may not be worth buying an amp/dac.
Most headphone outputs are of a good standard now (though not as good as a dedicated amp) with the main issue for most people being they don't get loud enough.

I'd suggest trying listening to more dynamic albums at louder volumes and see if you notice a difference.

 

[TheInquisitive1]

So I was listening to various non-FLAC songs on Spotify (Mainly to see if there was a difference), UNAMPED...

Mos Def ft. Ronny Jordan - A Brighter Day
Ella Fitz. - Give Me The Simple Life
Max Romeo - Chase The Devil
Rainbow - Gates Of Babylon
Grateful Dead - Friend Of The Devil


They all sounded DIFFERENT from what I REMEMBER from my Ozone. I'm trying to 'get used to' them and then try the ozone instead of frantically swapping back and forth.

I'm yet to try the O2 with mp3's, but at least I'm hearing SOMETHING else (I think...)

 

[Brooko]

What you need to do (trust me - this works).
 
Spend at least 48 hours with just the HD600 and O2/ODAC.  Don't swap anything else.
 
At the end of that period - first try HD600 with different source (ie unamped).  A/B them.  If you don't notice a difference - celebrate, and sell the O2/ODAC.  They'll sell pretty easily on here - always in demand.
 
After that, try A/Bing your HD600 vs Ozone.
 
If you're still adamant that there are not enough difference to warrant the purchase - sell or return the HD600.  Then log off from Head-Fi and delete your history 

.  You'll keep your sanity and your money.
 
I think you'll find that after 48 hours with the HD600 (amped properly), and not continually A/Bing, you'll finally get to hear the differences we're talking about.

 

[Headzone]

Running HD600 without amp? No. Just keep the O2 in the chain, trust me.
 
Also the method Brooko said I recommend trying that. There IS difference, maybe you will not hear it yet but then your wasting part of HD600's potential anyway.