OK, so yesterday I acquired a second hand set of KR 242's. Put them in my B7, waited half an hour for warm up, and then started playing some music. It was instantly obvious that they reveal more detail and have a more palpable 3D effect than the 101D's but . . . on some tracks (seemingly those high with higher peak output) louder higher frequency sounds were distorting quite badly.
I have read throughout the various Lampi threads that the 242's output is an issue, and can overdrive the input on a pre-amp - is this what might be happening here? I did have to reduce the preamp volume from about 38 to 30 (max is 80), but that volume was otherwise fine at that level.
The input overload limit on the ML 585 I was using is 5.5v (44k Ohm input impedance). Is it likely that the 242's in the B7 (which has a 600mV output with KR 45's installed as per the Lampi measured spec sheet) is over-driving the input on the 585, or could there be an issue with the tubes? If it was an issue with the tubes would they distort on all tracks, rather than just the dynamic peaks of certain tracks?
Once I secure a new power amp, I can revert back to my ML 326S, which has a max input of 13.2V (100k ohm input impedance), which should give more headroom for the 242's, if that is the issue.
I do have some 20dB inline XLR attenuators - not something I would want permanently in the signal path, but would they allow me to reduce the signal from the B7 into the 585 to see if it eliminates the distortion?
Another option is to engaging headroom management in Roon to reduce the input level of the tracks going into the DAC - or is this unlikely to affect the output from the B7 into the 585?
Any thoughts from technically minded folks who can calculate such things? Is there a way for an end user to test the output voltage of the B7 with various tubes installed?