Mesa Boogie Big Block 750 at 2 ohms?

[JosephLB]

Yeah, I know the 750 watts is for a 2 ohm load but has anyone here ever actually done it? I just got a second Ampeg 212AV and I'd love to use them both but the head is old and I really don't want to damage it. I figured I'd ask here before I try it.

 

[agedhorse]

We no longer recommend any of the MOSFET bass amps into a 2 ohm load.

The MOSFETs ended up being inconsistent across multiple production lots and we didn't discover this for several years after the original manufacturer went out of business and follow-up manufacturers didn't quite get it right.

Also note that in some cases we can no longer repair these amps because some parts are no longer available. Those that we can repair tend to be expensive repairs.

 

[JosephLB]

We no longer recommend any of the MOSFET bass amps into a 2 ohm load.

The MOSFETs ended up being inconsistent across multiple production lots and we didn't discover this for several years after the original manufacturer went out of business and follow-up manufacturers didn't quite get it right.

Also note that in some cases we can no longer repair these amps because some parts are no longer available. Those that we can repair tend to be expensive repairs.

Thank you! I'm really glad I asked before diving head first into it!

 

[SteveFromBerlin]

Yeah, I know the 750 watts is for a 2 ohm load but has anyone here ever actually done it? I just got a second Ampeg 212AV and I'd love to use them both but the head is old and I really don't want to damage it. I figured I'd ask here before I try it.View attachment 7355653

You could use something like a Palmer Cab Merger. It doesn't cost much and brings the impedance back to 8 Ohm. It will still sound a lot fuller / better dispersion / more 3D when using 2x212 vs only one.

 

[KevInDaBassment]

You could use something like a Palmer Cab Merger. It doesn't cost much and brings the impedance back to 8 Ohm. It will still sound a lot fuller / better dispersion / more 3D when using 2x212 vs only one.

If they made a SpeakOn version with genuine Neutrik plugs I'd buy one immediately.

Noob, non-electrician question but would something like that have a wattage limit on how much it can handle? I'm guessing any wiring that's too thin will fail if you put too much into it, but I didn't see anything mentioning like "Do not exceed 300w of power" on it.

 

[blr2]

If they made a SpeakOn version with genuine Neutrik plugs I'd buy one immediately.

Noob, non-electrician question but would something like that have a wattage limit on how much it can handle? I'm guessing any wiring that's too thin will fail if you put too much into it, but I didn't see anything mentioning like "Do not exceed 300w of power" on it.

Palmer don't specify max power for this box, but it's logical to have a certain power limit. Best write to them and ask. Make sure to get both continuous and peak power ratings.

 

[agedhorse]

Just beware when using devices like that on an amp with bridged topology (like most class D bass amps). If the case is tied to the speaker minus terminal, and it touches anything grounded (like any amp chassis), it could damage the amp.

These are made for used with guitar amps that rarely use a bridged topology.

 

[blr2]

Just beware when using devices like that on an amp with bridged topology (like most class D bass amps). If the case is tied to the speaker minus terminal, and it touches anything grounded (like any amp chassis), it could damage the amp.

These are made for used with guitar amps that rarely use a bridged topology.

Very good advise. IMO, this box was made primarily for guitar tube amps up to 100 W, so you can mix and match cabs to the particular impedance of the output transformer.

 

[Rip Van Dan]

You could use something like a Palmer Cab Merger. It doesn't cost much and brings the impedance back to 8 Ohm. It will still sound a lot fuller / better dispersion / more 3D when using 2x212 vs only one.

I'm guessing that's a series connection box? If not, a series connection box should do the trick. A series box used between the cabs will turn two 4Ω cabs into an 8Ω load instead of a 2Ω load that the industry standard parallel connection will do.

I still have a Sunn B202 cab (212 cab) and it has both a parallel out and a series out on the back of that old cab. It was a life saver because it's a 4Ω cab and my GK Backline 250 has an 8Ω minimum load that never seemed to get mentioned in their ads. It came as a set with a GK 115bpx, which is the worst cab GK ever made, and it only had an input, no output jack for daisy-chaining. So I hooked my 4Ω cab up first to the amp and then used the series output from the Sunn to the GK115bpx. That put a 12Ω load on the amp (4Ω+8Ω in series = 12Ω) and its power dropped from 125-watts rms to somewhere around 85 or so. But the extra two 12" speakers not only made it sound a lot better, it was actually louder than the 115 by itself, even with that power drop. So get that cab merger or some other series box and go for it. You will sill get at least a 3db gain in SPL from the extra speakers pushing more air than one cab.

 

[roccobass]

We no longer recommend any of the MOSFET bass amps into a 2 ohm load.

The MOSFETs ended up being inconsistent across multiple production lots and we didn't discover this for several years after the original manufacturer went out of business and follow-up manufacturers didn't quite get it right.

Also note that in some cases we can no longer repair these amps because some parts are no longer available. Those that we can repair tend to be expensive repairs.

Thanks for the info on the current status of these Big Blocks in relation to Mesa. Wow. I almost turned a local CL ad on to my buddy in Tennessee who comes out here often. He was thinking how cool it might be to pick one. I didn't know they could be problematic. The guy here is selling his rack mounted BB, (along with the rack, tuner and Furman power conditioner) for $1200. I thought that was a good price. But here I am reading your post and now wondering. He insists all is well the all with the equipment. Ya takes ya chances, that's for sure. I dunno.

 

[agedhorse]

Thanks for the info on the current status of these Big Blocks in relation to Mesa. Wow. I almost turned a local CL ad on to my buddy in Tennessee who comes out here often. He was thinking how cool it might be to pick one. I didn't know they could be problematic. The guy here is selling his rack mounted BB, (along with the rack, tuner and Furman power conditioner) for $1200. I thought that was a good price. But here I am reading your post and now wondering. He insists all is well the all with the equipment. Ya takes ya chances, that's for sure. I dunno.

If there are no problems, it's a great deal. I'm just providing full disclosure so that you can make an informed decision.

 

[roccobass]

If there are no problems, it's a great deal. I'm just providing full disclosure so that you can make an informed decision.

Thanks. I'll relay everything to my buddy.