[Arran]

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Results: the base of this thing is overpowering. Has to be subdued with the bass knobs, or it is really booming. Also need some weatherstripping under the glass: it vibrates when the base is strong. But I do like the sound.

Mike;
  You probably would not wish to do this now, but there is something you could try to deal with the overpowering bass. I would suggest experimenting with the tone correction capacitors C35 and C36, either by taking C35 out of circuit, and or changing the value of C36. I think that the issue is that these are cutting the treble down too much and accentuating the low end.
Regards
Arran