Hum and Hiss from Sonic Frontier Preamp

Last night was the first time I used my head phone jack from my SF line 2 pre amp. There's a subtle hum and an occasional hiss when the pre amp is on. Does any one have this problem or know what causes this problem? The only upgrade I made were changing the standard 6922 tubes to valvos tubes. Thanks in advance for all your help. Btw, there's a slight hiss when I play my front speakers as well, but it's not as noticable or as anoying as when I use the head phone.

Showing 2 responses by 7p62mm

I agree completely with Sgmlaw. I have a line three and there is a slight hiss that is audible if you place your ears next to one of the speakers with no active source. Increasing the volume control does not change the hiss amplitude appreciably which indicates that the hiss is part of the noise floor. I used to own an ARC LS22 and it acted the same way. I have no experience with solid state preamps but my experience with SS amps indicates that their noise floor should be inaudible. I am curious as to how the sound quality of a good quality SS preamp compares to my Line 3 (which sounds great).
I forgot to mention that I have never used headphones with the Line 3.