I posted these observations in another thread, but perhaps it is worth repeating them here.
"A week or two ago I got my Yamaha C-4 pre back from a complete re-cap. This is a unit that is 35 years old, typically runs fairly warm and plays an average of 10 hours per day so the work was done as a precautionary measure. It had been problem-free and sounded good so I wasn't expecting much real change in performance. When I first hooked it back up in its usual system (C-4/Epicure M1/Vandersteen 2C) the bass was noticeably leaner than previously and the top end brighter. Over the intervening time the bass has returned to normal (perhaps even going a touch deeper), but the treble is still hotter than before. I'll give it another week or two and if it doesn't settle in I will turn back the tweeter control a bit.
In another aspect I really got a surprise, though. The sound stage with the combination has always been quite satusfying. The space the system is in is about 15' wide and 25' deep. I have the speakers about 9' apart on either side of a fireplace and generally sit about 8-10' away. The perceived stereo image has never extended much to the outside of the speakers. Imagine my surprise when listening to a favourite jazz quartet recording when the upright bass was suddenly positioned approximately 4' to the right of the right speaker whereas when listening to the same recording before it was always right at the speaker. The piano now seems extended from left of centre to perhaps 3' outside the left speaker. The image also seems noticeably taller and more coherent. Spatial detail is also clearly improved. Anyone have an explanation for this? I wasn't expecting anything of the sort, but it is impossible to ignore. Please note that none of the caps removed tested bad, not a one."