[High_Q]

I have this amp:
 
http://www.head-fi.org/forum/thread/410886/elekit-tu-882-vacuum-tube-5670w-x-2-headphone-amp
 
 
 

1. Vacuum tube / 5670W×2
2. Rated output / 200mW(RL＝6Ω or 32Ω or 600Ω)
3. Output impedance / LOW 4～20Ω、MID 20～100Ω、HIGH 100～1kΩ
4. Rate input / 400mV
5. Input resistance / 50kΩ
6. Frequency response / 20Hz～50kHz
7. S/N 102dB(IEC WEIGHTING)
8. Voltage / AC120V 50/60Hz
9. Dimension / W130×H120×D250mm
10. Power consumption / 10W

 
 

 
And I am getting distortion at low impedance setting(4-32ohm) for my HD800.  Can anyone explain how output impedance reacts with headphones of difference impedance?  HD800 is 300ohm. Why would it distort at low impedance setting, my HD650 doesn't, I though lowest output impedance setting is desireable for damping?

 

[Tilpo]

Unless there is an output transformer (which I don't think there is), then impedance settings usually just mean gain, i.e. high impedance is high gain. This should, however, not create any distortion as you described.
And with distortion, do you mean the sound is distorted, or do you mean that there is background noise?
Another thing to consider is: did you solder it yourself, or did you get the PCB assembled version? If you have soldered it yourself, it might be caused by some bad solder joint.

In any case, it'd be best to contact the manufacturer/supplier of the amp. This should not happen, and it might be a defect in the amp.