I installed some NOS RCA VT-231's in my LS100 yesterday. The first thing I noticed was a low level tone that would rise in volume with the music. It sounds like a test tone and is in the right channel only.
I decided to let the tubes run in and hooked up a DAC to play continuously via the XLR inputs. The right channel tone went away. Now the left channel is clipping with strong bass notes, but that's an issue for another thread...
Getting back to the test tone issue, I looked up the output impedance of my Zesto Andros phono stage and it seems pretty high at 10k. The input impedance of the LS100 is listed at 39k, which seems pretty low. I have read that that the general rule of thumb is 1:10 (output:input) so I suspect I've just created an expensive compatibility problem.
I haven't tried any trouble shooting yet (swapping tube positions, swapping tubes, etc) although I can say the tone was not present with the Russian current production tubes that came with the used LS100.
Does anyone have experience with the Zesto/LS100 combo or suggestions on what to try?
Todd