[blackzarg]

So, I just got my first amp, and I've been using my headphones with it. My setup is Macbook Pro 2007 > Nuforce uDAC > AV123 X-Head.
 
I've been trying my headphones out with it, and I noticed that I'm getting some hissing that wasn't there before from some of my headphones (in my signature). I get hissing from most of my headphones, except the AKG K240 Monitors, which are 600ohm.
 
The funny thing is, I had regretted getting the AKG's because they never sounded good, but now they sound great with the amp, and everything else has an annoying hiss.

 

[Ypoknons]

Try different outlets or a cheater plug (plug without a ground), it might be a ground loop.  wait, nvm... you're not getting it from the K240? hhmmm maybe not a ground loop then. 

 

[kboe]

Are your RCA cables directional? If so, check to see that you have them in the right direction, and then correct them if not.

 

[blackzarg]

I don't think they're directional... these are the ones that I have:
Monoprice Link
 
Thanks for your help in troubleshooting this, guys!

 

[High_Q]

The output of the amp is at high impedance if it is hissing.  Typically headphones around less than 32 ohms that have high sensistivity, will cause hissing because of the impdedance imbalance.  Is there impdedance setting on the amp?  If so, try lowering it low as possible.  Or maybe get an impdedance adaptor to increase the impedance of the highly sensitive headphones.

 

[blackzarg]

Thanks for that explanation. I wish I had another pair of low sensitivity phone to try them out with, but the main reason I got the amp was in preparation for an AKG K702, so I guess I'll just wait until I get that and solely use the amp for the two AKG's I have.
 
The other phones I'll just plug into my uDAC.
 
Quote:

The output of the amp is at high impedance if it is hissing.  Typically headphones around less than 32 ohms that have high sensistivity, will cause hissing because of the impdedance imbalance.  Is there impdedance setting on the amp?  If so, try lowering it low as possible.  Or maybe get an impdedance adaptor to increase the impedance of the highly sensitive headphones.

 

[kboe]

Id bet those are not directional.  You actually have a good enough entry level system and resolving enough headphones that a good set of RCA cables should make a noticeable improvement.  Your ears might just be sensitive like mine are.  I recently had to sell an amp because I could hear the background hiss.  Drove me nuts. 

 

[Ham Sandwich]

Did you get the x-head new or used?  The first version of the x-head was supposed to have a shielded transformer but got built with an unshielded transformer and that caused some hiss.  The second version of the x-head got a redesign and a relayout of the circuit board to fix the hiss.  The second version should sound clean and free of hiss.
 
The second version has a sticker on the bottom that will say "Rev B".

 

[blackzarg]

It's a Rev. B model. I had one new a year ago, sold it, but recently bought this one used (pretty much new/unused) for a good price.
 
Quote:

Did you get the x-head new or used?  The first version of the x-head was supposed to have a shielded transformer but got built with an unshielded transformer and that caused some hiss.  The second version of the x-head got a redesign and a relayout of the circuit board to fix the hiss.  The second version should sound clean and free of hiss.
 
The second version has a sticker on the bottom that will say "Rev B".

Gosh, the K240 Monitors had been sitting around for the longest time, but they are so fun to listen to now! I wish they were a bit more comfortable, though - the pads squeeze my ears. I just called AKG and ordered a pair of velour earpads to replace them.
 
Heh, I'm probably selling a few of my sets to get $$ for a K702.... I think the Denons and the Grados will go... (possibly a Sony V6 as well).

 

[Ham Sandwich]

If you use the x-head with no source connected do you still hear any hiss if you turn it up?
I have an x-head (rev b) and it is quiet, no hiss with my headphones.

 

[blackzarg]

Hmmm...Unfortunately, yes. Perhaps it's my power outlet. Well, this isn't too big of a deal for me - I have my uDAC for the high sensitivity phones. I'll just use the X-Head for the AKG's.
 
Quote:

If you use the x-head with no source connected do you still hear any hiss if you turn it up?
I have an x-head (rev b) and it is quiet, no hiss with my headphones.

Thanks for your help!

 

[angle_sh00ter]

I can't put up with even the slightest hint of hiss or noise coming from an amp.  If I'm gonna spend decent money on a headphone system I want a clean signal with a black silent background.  
In my experience tho it is low impedance headphones which are usually the culprits, not the high impedance phones.

 

[kboe]

Couldn't agree with you more.  Its why I just sold my last amp and am going to be buying a RSA XP-7, which is said to have a black background. 

 

[Skylab]

I think we need to differentiate "hiss", from "hum".  If we are talking about "hiss", then this is not a grounding issue.  Let's assume that is the case.
 
Some amplifiers have enough intrinsic noise that if you have a very high-sensitivity headphone, you might be able to notice it with no music playing.  With almost any amp, if you crank the volume all the way up to the top, you will hear some hiss through almost any headphone (again with no music playing).
 
Further, some SOURCES will have enough noise that this will be audible though the amp - and this is not the amp's fault!  Also, some amps will hiss when there is no source connected, but won't when the source is connected but turned off (this is an amp topology issue).
 
Finally, a very small amount of hiss may actually be a good thing, in that the way this is supressed sometimes is by using global negative feedback in the amplifier circuit, which many people (me included) believe had have a negative impact on the sound.
 
Bottom line - it's pretty common to have some level of hiss.

 

[angle_sh00ter]

I guess I mean audible noise.  With my Burson amp there is no noise or hiss (audible to me) even at the highest volume level with no music playing (with any of my headphones)