Slight hiss coming from headphone amp's with no music playing on my desktop

[rilgon]

Hello. I own a couple of cheaper headphone amplifiers, being the ELE EL D02 amp/dac and the Fiio e11 portable headphone amp. I notice that when I do not have any sound going on my desktop there is a slight hiss in the background. When music starts playing the hiss is gone and the quality is fine. The hiss is a bit louder on the ELE, but it is present in both. The ELE also has a line out port and if I plug in my headphones through there then the hissing actually goes away, with the loss being that it seems the amplifier is not as loud, but the sound quality is comparable when the volume is turned up enough. The headphones that I use are NVX XPT100 and Creative Aurvana Live!, if that is of any use. I am just curious if this sort of hissing is common in cheaper amplifiers, or is it often attributed to some other issue? Thank you.
 
http://www.ebay.com/itm/PCM2704-USB-DAC-TDA1308-Headphone-amplifier-Volume-Control-ELE-EL-D02-BLACK-/230963476750
http://www.amazon.com/FiiO-E11-Portable-Headphone-Amplifier/dp/B0053KWDES

 

[NA Blur]

It is common in poorly designed and higher outout impedance ams. Expensive amps can suffer from this as well especially tube amps as they typically require more power to drive meaning more noise is in the board and they typically have higher out put impedances. You can read more about imedance, damping, and distortion if you need a refresher.

 

[fabio-fi]

Did the hiss started recently, or has it been there always? 

 

[rilgon]

I just got the ELE EL D02 about two weeks ago and the hiss has been there with those since I received them. The Fiio I mainly used with my ipod but since getting the NVX XPT100 I started to use them together at my desktop since it didn't feel like my on board audio was driving them enough for me at their 64 impedance, and the hiss was apparent there as well upon first use with my desktop. The ELE hiss is also present on my laptop, and the Fiio I can't really sense a hiss with on the laptop.