[ctviggen]

Hi All,

I've used two different tube-based headphone amps.  My current headphone amp is the Little Dot I+ 6JI X2 Tube standard Hybrid Headphone Tube Amplifier:

http://www.amazon.com/gp/product/B00A2QM5O6?psc=1&redirect=true&ref_=oh_aui_search_detailpage

I'm using the AUDIOQUEST - DRAGONFLY V1.2 USB DAC before the tube amp. See:

http://www.theabsolutesound.com/articles/audioquest-dragonfly-usb-dac/

The chain of music is as follows:  I go from music player through USB to the Dragonfly DAC to the tube amp to my headphones. 

The problem is that I go through tubes quickly, sometimes in a few weeks or less.  When my last set of tubes started making strange noises, I took the tube amp out of the chain, connecting my headphones back to the Dragonfly DAC.  (So, music player -> USB -> Dragonfly DAC -> headphones.)  The sound was LOUDER than when the tube amp was in the loop!  That is, the tube amp had actually decreased the loudness. 

Could I be going through tubes quickly because the Dragonfly DAC is over driving the tube amp?

Unfortunately, I have no tubes right now, so I can't test what would happen without the DAC in place.  Plus, I like using the DAC, as it makes things sound better.

[kingdeezie]

If I read the dragonfly specs right, it outputs 2Volts. That's the digital output standard I think. That shouldn't overdrive a headamp.

If you are burning tubes like that, I would suspect something is wrong with the headamp itself.

[FullRangeMan]

Avoid chinese tubes if possible, look for US tubes.

[JohnR]

I'm inclined to agree with kingdeezie, there has to be something wrong with the amp. Tubes should last a long time regardless of signal level.

[raindance]

What happens that makes you think your tubes are bad? These tubes should last a long, long time - like 100,000 hours - are you perhaps rolling tubes that are not exact substitutes for the originals?

No, you cannot mess up your tubes by overdriving them. All you'll get is distortion. In this amp the tubes are not used for power output, they use transistors for that. Did someone perhaps swap out the op amp with one that isn't working right?

Volume levels are meaningless as they are dependent on gain structure. Where the knob is set means nothing.

This isn't a tube headphone amp. It is a tube hybrid meaning the tubes are used to slightly "flavor" the sound.

[ctviggen]

Sorry, I posted this before I went on vacation.

I've had multiple sets of tubes fail within a few weeks at most. 

Maybe I have to buy a better tube-based headphone amp?  They get to be a bit expensive, though. 

[raindance]

Please answer this question: what makes you think the tubes have gone bad?  What tubes are you using? These are decent amps.