A couple of thoughts: 1) You shouldn't get audible hiss from 9ft away at normal listening levels from ANY amp
2) the hiss reduces with new valves then quite rapidly comes back (2 months?) 3) the output impedance of the 2.5 is 200 ohms, the input impedance of VTL's own power amps is 100k 4) hissing noise is not due to impedance problems IME - and according to the specs you shouldn't have a problem anyway if everything is working properly 5) I suspect that you have a faulty resistor or capacitor in the pre-amp - or possibly a fault in the valve heater circuits. New valves cause a change in bias conditions but over time the underlying fault causes the new valves to deteriorate. I've seen this in valve guitar pre-amps. 6) It is possible a fault is damaging the valves - do you have an old set? - swap them out with the current set and see if the old ones immediately hiss. H 7) How does the hissing change with the volume and mute controls on the pre-amp? is the hissing identical on left and right channels? 8) You commented that the top end sounds rolled-off... but the specs say the preamp goes to 60kHz -3dB... that seems odd. Finally, try this. I believe your preamp has two 12AU7 and 2 12AT7 valves - try swapping the valves of the same type with each other. It's very rare for more than one valve to develop an identical fault at once in a pre-amp. If the hiss stays the same I'd strongly suspect a faulty resistor. It's hard to diagnose/suggest further without a circuit diagram. I urge you to get the pre-amp serviced professionally. -- Phil Leigh You want to see the signal path BEFORE it gets onto a CD/vinyl...it ain't what you'd call minimal... SB3 (wired) - TACT 2.2X (Linear PSU) + Good Vibrations S/W - MF Triplethreat(Audiocom full mods) - Linn 5103 - Aktiv 5.1 system (6x LK140's, ESPEK/TRIKAN/KATAN/SEIZMIK 10.5), Townsend Supertweeters, Blue Jeans Digital,Kimber Speaker & Chord Interconnect cables Outdoors: Boom ------------------------------------------------------------------------ Phil Leigh's Profile: http://forums.slimdevices.com/member.php?userid=85 View this thread: http://forums.slimdevices.com/showthread.php?t=63739 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
