New Rachel and Monolith owner here testing out a ZStage addition to my already used system. Yesterday I noticed some background distortion that I had not heard before in one of me test songs. I took out the ZStage but the distortion remained, in the background but audible. Any suggestions where I might start looking for the source, I’ve heard this particular song many times and this was the first I’ve heard that grit in the background.

Hi Richard,
It was like old fashioned radio drift but it didn’t seem to affect the vocals or drums (but their dynamics are all peaks) just grit on the instruments. I was surprised to hear it or even that I could after a loud career. I’ll spin some other discs and then revisit that song. I don’t have a spare set of input tubes so I can’t really do a logical path thru the amp.

Might be several tubes at the same time. I’m pretty sensitive to wire routing and leaky digital pieces but just in case I pulled the ZStage out of the signal path and off the CD transport. No joy. The mail brought some new 6N2P input tubes so I was able to replace each section, as I did the EL-34s started sounding pretty janky. Eventually after swapping outputs twice I landed on KT-88s that weren’t too unhappy with a GZ-34 rectifier  so maybe the Valve Arts 274 is failing and the EL-34s are going with it. I don’t know the age or hours on anything which has prompted a tube order for the whole amp so I can start from the beginning.