Got the shorting RCA plugs I had ordered - hiss is almost completely gone. I can hear it still with the volume dial 3/4ths of the way, but that is way beyond any listening level I'd be driving it to. The hiss is now gone when turning the gain dial too.
The other thing that made big difference was leaving the tubes on 24/7. Might be partly due to some breaking in, but the preamp has now been on for the past week (standby mode when not listening) and that has made a significant difference in overall sound as well.
The other thing that made big difference was leaving the tubes on 24/7. Might be partly due to some breaking in, but the preamp has now been on for the past week (standby mode when not listening) and that has made a significant difference in overall sound as well.