Everyone forgot one thing. Turn off your preamp and clean the pins of the tubes. Use an exacto knife and then clean with a contact enhancer or alcohol. Shake dry then re-insert tubes. Turn the unit on and let it sit for about 15 to 30 minutes. Test tubes! Try some different ECC88 / E88CC / 6DJ8 / 6922 / E188CC / 7308 / CCa / E288CC / 8223 tubes. You may want to check your music store(s) for some of these tubes so you won't have to wait for them to arrive.
Last, check to see if the unit has been modified, etc. There are some parts swappers out there that will make changes and won't tell you. One other thing. . . take it to a local dealer for audiophile friend that has some tubes and listen to it there.
The preamp should not have any brightness or extra sibilance in it's sound. That's not an Audible Illusions trademark. If all fails that unit is defective!!!!
Good Luck
Last, check to see if the unit has been modified, etc. There are some parts swappers out there that will make changes and won't tell you. One other thing. . . take it to a local dealer for audiophile friend that has some tubes and listen to it there.
The preamp should not have any brightness or extra sibilance in it's sound. That's not an Audible Illusions trademark. If all fails that unit is defective!!!!
Good Luck