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Overheating

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rickeb1:
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

Harley Hexxe:
Hey RickeB,

    A fan is always a good idea in a rack. I like my rack cases with front and rear rails because I can mount rack panels with fan cutouts in the back and place them where they need to direct air the most. I don't space my rack units apart, so it was planned that way.

     Harley 8)

rnolan:
Hey Rick, what a bugger... Was the DCM150 hot when you took them out ?  MP2s get very hot and IMO need a little air around them, my guess is that's where most of the heat was coming from (apart from the sun), not sure of the symptoms though, where the bad sound was coming from, maybe the amp ? I've never had that with a MP2 but then I've never put mine quite in that situation (padded bag/rack, sun).
You should be ok with a 2RU normal rack (skb, gator etc). I put my MP2 at the top as then there's a reasonable gap (~3/8" ish) above it for the heat to dissipate.  The MP2 is quite a deep unit.  I've been looking at racks lately and there seems to be 3 common depths:
Shallow - 10.7" (27.48cm)
SKB ATA cases - 15.94" (40.48cm)
Deep - 17.6" (44.7cm)
The SKB ATAs are the perfect depth, the shallow may not close on the cables comfortably ?? and also has no room for a power board and the deep ones are way to deep.
A 3RU would be nice and give you a space for a multi FX, but then why not 4RU (space for a B200s LoL).  My feeling is the padded bag/racks are more designed for low power SS gear, not tubes.  With a decent rack you shouldn't need a fan, but it can't hurt, mounting it is another story...or buying a rack with a built in fan $$$ ??

MarshallJMP:
Like R says,those MP-2 get hot after a while so I also have a fan in my rack because else it will overheat.

rnolan:
Hey MJMP, have you ever had a MP2 overheat ? does it go all thin etc like Rick is describing ?
I think the only thing I've got that gets hotter than the MP2 is the B200s, you can cook your breakfast on it...

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