[ZianC]

Based on Wikipedia and an article on Head-Fi (http://www.head-fi.org/a/explanation-of-amp-pre-amp-headphone-amp), my understanding is that a headphone amp takes a signal (say, from a computer's built in 3.5 mm jack) and amplifies it. This is very helpful for "bigger" or "more demanding" headphones and is a necessity with certain types of headphones.
 
My IEMs sound fine without an amp and certainly aren't big. Therefore, I've never been interested in amps.
 
However, I need a DAC that connects by USB to get around hissing noises from my ThinkPad that are somewhat perceptible with a pair of Senneheiser PX100 and are truly awful with Brainwavz IEMs.
 
I would like to believe that I do not need to get an amp to go along with a DAC based on the following reasoning:
 
Given:
- Tiny IEMs
- A USB-powered DAC provides a bit of power (though not necessarily a ton)
 
Then: A USB-powered DAC should provide enough power for a pair of IEMs.
 
Is this reasoning sound?
 
Let's say that I buy...an ODAC...Is the reasoning still sound?
 
I'm going to do a little number crunching based on info from Brainwavz and info from Northwest Audio Guy but I'm new to this sort of mathematics so I don't want to use my calculator without a "sanity safety net" in case I screw up.

 

[fluffygdog95]

If you buy a pure DAC, you will need to have some form of amplifier to which you connect the line level outputs. A DAC alone can not be used with headphones, or is highly not advised. I recommend browsing the forums for some amp/DAC combination units if you're looking for a one box solution to your noise problem.

 

[PurpleAngel]

  Based on Wikipedia and an article on Head-Fi (http://www.head-fi.org/a/explanation-of-amp-pre-amp-headphone-amp), my understanding is that a headphone amp takes a signal (say, from a computer's built in 3.5 mm jack) and amplifies it. This is very helpful for "bigger" or "more demanding" headphones and is a necessity with certain types of headphones.
My IEMs sound fine without an amp and certainly aren't big. Therefore, I've never been interested in amps.
However, I need a DAC that connects by USB to get around hissing noises from my ThinkPad that are somewhat perceptible with a pair of Senneheiser PX100 and are truly awful with Brainwavz IEMs.
I would like to believe that I do not need to get an amp to go along with a DAC based on the following reasoning:
Then: A USB-powered DAC should provide enough power for a pair of IEMs.
Is this reasoning sound?
Let's say that I buy...an ODAC...Is the reasoning still sound?
I'm going to do a little number crunching based on info from Brainwavz and info from Northwest Audio Guy but I'm new to this sort of mathematics so I don't want to use my calculator without a "sanity safety net" in case I screw up.

 
An external DAC with a built in low impedance headphone amplifier should improve the audio quality of any IEM or headphone, used with your Thinkpad.
Fiio E17 external DAC/Amp, should be able to find a used one on eBay for around $100 to $110.

 

[kraken2109]

A DAC will give you a line level output with no volume control. That's not exactly ideal.

 

[PurpleAngel]

  A DAC will give you a line level output with no volume control. That's not exactly ideal.

 
I use an external DAC and can still adjust the volume thru Windows.

 

[kraken2109]

   
I use an external DAC and can still adjust the volume thru Windows.

Software volume control isn't ideal in terms of S:N ratio, but I guess it would work. It's certainly a faff not having a dial to use though, e.g. when playing a game there would be no easy way to adjust volume.

 

[vkalia]

A DAC may have a higher output impedance than ideal for headphones.
 
However, you are correct - as you have (most likely) sensitive IEMs, you dont need a brawny amp.  What you need is a DAC/amp unit that has a high S/N ratio and gain that is suitable for IEMs.