Distortion in the upper bass/mid frequencies

[Souter]

Hi, I'm getting distortion (sounds like the music is breaking up) in the upper bass/mid frequencies when playing loudly.
It is not noticeable at low volumes.

I'm using a modded t50rp headphones for listening.

Any ideas anybody? Could it be the tubes? (stock)

Advice would be much appreciated.

[Doc B.]

The T50RP is  50 ohms impedance and the Crack is designed for headphones of 200 ohms or higher impedance. That mismatch is likely the root cause of the distortion you are hearing.

[Souter]

Thanks Doc, would you not recommend the HD700 or HD660s then? (both 150 ohms)

[Paul Birkeland]

Those will work well with the Crack as well.

[Souter]

Thanks a lot.