I just played a gig yesterday with my very small "B" rig which consists only of an MP-2 and an old Carvin DCM150 power amp. These are housed in one of those 2-space padded rack bags which are very shallow, just enough space in back to close behind the units.
I'd played a few gigs with this setup previously, and all went well. At yesterday's gig, we played outside in the sun, and it was very hot and humid. About half way through the first set, my amp started sounding weird. It seemed to lose all body, and had only a very harsh high-end. I remembered reading about something called "thermal distortion", and guessed that something was overheating. When the set ended, I grabbed a screwdriver and took the units out of the rack and placed them on top of the rack (back-to-back since I had only a short cable to connect the two), hoping that the added ventilation might solve the problem. And it did seem to work, as I didn't get that weird tone the rest of the gig.
I'm wondering what I might do to ensure I don't have such a problem again. I'm assuming the problem was in fact overheating, caused by the direct sun, high temps and humidity, and the close, tight rack enclosure which offers virtually no ventilation.
First, which piece do you think was the main source of the problem, the MP-2 or the power amp? If I bought a different rack case, say a 3-space one and put one unit on top and the other on the bottom with a blank space between them, would that likely do the trick? Or maybe another 2 space rack (I'm trying to keep things as small as possible) that is deeper, allowing more air? Maybe a fan of some kind?
Thanks for your thoughts on this!
~Rick