Hi All;
This issue has been persistent for a while now, and I did talk briefly with MJMP about it a few months ago. I noticed it after I reversed the 3.666 mod on my first MP-1 (I have 3 now), so I probably messed something up, but maybe not, too. Here goes:
On any voicing (SS Clean, tube clean, or dist), if I run OD1 somewhere around 5.0, and give the guitar a hard strum, the OD1 LED goes on solid, and the whole thing gets distorted, in fact, even SS clean will act like I've stuck a fuzz box in front of the amp. If I stop playing, it will "calm down" after a second or two, as though extra voltage is being dissipated (bad cap?). When it started months ago, MJMP and I went through a few things, including measuring voltages at various ICs, and swapping chips between this unit and one of my working ones, to no avail. Then I gave up, thinking I could live with it - just use it in my studio, and not dial OD1 higher than the "tipping point", but now it's become problematic.
The tube board in this unit is in rough shape, with lifted and repaired traces everywhere, but it works OK (I don't trust it in its current state for road/live use though), and since this issue occurs even in SS mode, when the tube board isn't involved, I'm thinking the tube board isn't likely to be the source of he problem. I've ordered some VTL5c4/2's from Small Bear, just to have a couple on hand (they're getting harder to find, so thought I'd stock up), but I doubt they're the culprit. From what I understand, vactrols either work or they don't; they're not usually flaky like this. Maybe I'm wrong on that.
Any ideas? I'll also email MJMP later today.