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I spent my Christmas cash on a Schiit Modi DAC and Vali headphone amp after reading some of the positive reviews here on Head-Fi.  They arrived at my office today, so I hooked them up, and there seems to be a lot of white noise coming out of the Vali amp.  I've read that Tube amps (even microtube ones like the Vali) have a "noise floor," but I feel like there has to be something wrong if it's putting out this much.

 

Here is how I've got it right now:

 

 

The DAC is connected to a MacBook Pro via USB, the amp is connected to the DAC via an Acoustic Research shielded RCA cable, and the Shure SRH440's are plugged in with a 1/4-inch adapter. With this setup, I hear a distinct static/white noise hiss whether music is playing or not.  It does not increase in volume when the amp's volume knob is turned up, nor does it change when I completely disconnect the DAC from the amp and run the latter without any input.  It's always there, as far as I can tell.

 

I tested the amp with another set of headphones, a coworker's Sony MDR-V6 set, and still heard the static.  I've also tried moving the amp away from other electronics (at least as far as I was able, since it's meant to be used with my laptop), but the static continued.

 

Is there something wrong with how I've got things set up?  Would headphones with more impedance help?  Is this level of white noise or hiss normal for this amp, and I just need to live with it? During some songs it's not that noticeable, but anything that has a quiet passage reveals it again.  Could there be something wrong with the amp?