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I have a question. I have my HK 3490 acting as a preamp for my headphone tube amp. I'm using the tape out of the HK to the input of the tube amp. And I have the speakers selected to OFF on the HK.

 

I have my LCD-2's attached to the tube amp and my Grado's attached to the HK headphone input. Everything works fine but I noticed if I remove the grado from the HK that my tube amp gain drops a little. Plug the grado back in and the HK switches into HP mode and the tape out sends a stronger signal, in turn my LCD-2 gets louder.

 

Can anyone explain to me why this is happening? Should I not have the HK in HP mode? It's a pretty big difference in output VS the HK not being in HP mode. (output to the tube amp via tape out that is.

 

One of you smart audio guys should be able to answer this one.