Mesa Big Block 750 Fried?

[dgdamore]

I bought this amp used about a month ago. The first gig I played with it, it performed flawlessly. Great tone and gobs of power. No problems at all. Last night, while setting up for our gig, it didn't sound right. I tried two basses through it, (a Rick 4001, and an active Fender P) They both sounded distorted and the overdrive was NOT switched on. Even worse, the amp was making very little power. I increased the master volume and gain and tried switching on/off the overdrive and overdrive levels to get something out of it and the volume at the cabinet did not increase at all. Then... poof, a slight pop, much smoke and no more sound at all. It was enough smoke that people were yelling "fire"! It smelled like something fried, but I didn't see any fire.

Luckily I had my trusty SVT4 as a back up and the gig went off without a hitch.

Today I opened the Mesa expecting the worst but found nothing at all that appeared wrong, certainly nothing that looked burned. (and no burnt smell) I tried it again but still no signal to the cabinet. All three fuses appear solid gray (not like the usually clear glass I'm used to seeing on cars etc.) so it's hard for me to tell if they are blown.

I plan on visiting the authorized Mesa repair guy this week unless you guys have any ideas?

FWIW I run it into a 4ohm 210 via speakon to 1/4" from one output and an unknown ohmage 115 via speakon to 1/4" from the other output. I thought mismatched speakers could be the problem, but owners manual states that any combination of speakers can be used so long as their total combined are not less then 2 ohms. I've been using this same combo for years with the SVT4.

Thanks for reading.

 

[Nightlyraider]

Visit your tech, there absolutely shouldn't be pops and smoke. Especially the smoke.

 

[bass10bfb]

I owned the Big Block 750 for about 2 years (bought it used) and when I first bought it had what sounds like the exact same problem. I had my tech check it out for me (I honestly can't remember now what the part was that he replaced but he said it was a common problem with the Mesa's). The part and labor cost me right around $100. The amp kicked butt night after night from that point on.
I honestly don't think the cabs are an issue at all. That amp is made to push two ohms all night long. I pushed two of the Mesa Powerhouse 1000 cabs with it for hours nonstop with no issue. It is a super powerful amp. I would assume that the unknown ohmage of that speaker cab surely would not be lower than 4 ohms, which would make the load 2 ohms total at that point, which would be ok.
I wish I knew the part name for you that was changed out. Hope I might have at least helped some. Good luck with the head. It is a monster and will sound awesome when you get it fixed!!!

 

[RickenBoogie]

It need to see an amp tech, and that's the truth.