Hi Dean ...
Specifically, I don't know about adjusting the attenuators but given the experiences below I'm not sure this is the answer ... particularly given that it's only reported to be prominently noticeable when the TSP circuit is engaged
.
I wanted to be able to add something more constructive so I contacted the producer who had the "most" problems here. He says:
(1) The distributors (very good people over here ... which is helpful because we're on the other side of the world) suggested that there was in fact some sort of design issue where the L/R outputs would mismatch by around 4dB if the Input/Drive level was set to less than -10 (I think?) and the TSP circuit engaged. The fix is obvious but may not be what you want on every occasion.
(2) Initially, they advised him to swap the valves around (not replace them, just swap them). FWIW I think this may have cured the other studio's problem but I can't be sure.
(3) They also warned him that the units were sensitive to ventilation issues and that the TSP circuit was particularly vulnerable. In other words, make sure that it's not overheating. Come to think of it, I remember that they threw in a couple of ventilator panels for the rack when I bought my 747 (see, they are good people).
(4) Unfortunately, none of these fixes really helped ... his other problem was that after waiting the advised 20mins for warm-up the unit initially functioned OK. But, when he stopped "play" (he runs a big ProTools HD system) and restarted it again one channel ... usually the left ... would drop in volume by about 4-6dB and the "tone" would perceptually change. It was like a fresh signal somehow triggered the fault. Really weird and seriously annoying. Eventually, he ended up sending the unit in for service. Not really sure what they did with it there (the service centre is at the other end of the country) but they did acknowledge that there was some kind of issue and apparently fixed it. Because they were kind of vague about what was done, his cynical suspicion is that they just fooled around with everything in the TSP and really aren't sure themselves what they did to remedy the problem. Anyway, the box is running OK now but still displays some mismatch symptoms when the drive level is set "too low" and TSP engaged.
I haven't had a chance to try to replicate the "too low/TSP in" fault on my unit yet as I'm a bit pressed at the moment.
I hope this is of some assistance, Dean.
Kind regards,
Paul