Mark V Head with 2 (16ohm) Cabinets Question.

[BrownieD2W]

I recently acquired a 4x12 speaker cab and I'm hoping to run both my 2x12 and 4x12 with the Mark V (90-watt version). After looking through the manual I realize that the 4ohmx2 Outputs from the amp to the 2x(16ohm) Cabinets is a safe-mismatch. The speaker impedance guide doesn't seem to show the exact layout of the Mark V with both pairs of 4ohm and 8ohm outputs. Is running both 8ohm outputs to two 16ohm cabinets even an option, and if not, could someone please elaborate as to why exactly?

My main questions to you guys is: What is the most efficient and most likely the best sounding option for hooking up two 16ohm cabs to the Mark V? 2x4ohm->2x16ohm-cabs, or, 2x8ohm->2x16ohm-cabs, What is the closest match I can achieve with both cabinets being run off of the Mark V? And are their any options that I'm not considering with this setup?

I'm mainly asking because there is a ton of conflicting information on this type of setup and the Pair of 8ohm Outputs to two 16ohm Cabs seems like it would be an option if the impedance of both cabinets is being cut in half roughly, but I'm not willing to gamble on that just yet. Any input would be appreciated.

 

[Monstercastle]

Diagram 11 on page 57 of the manual shows your situation, assuming that this is a head and not a combo with an internal speaker also connected. Two 16 ohm cabs connected to the two 4 ohm jacks is considered a "safe mismatch". I agree that Mesa's approach to this could be better. Perhaps it's just terminology. Two 16 ohm cabs connected in parallel present an 8 ohm load, so if you can daisy chain one cab off the other, you would be presenting an 8 ohm load to the head on a single jack. SO why don't they just call out connecting two 16 ohm cabs to the two 8 ohm jacks? I think you should connect the two cabs to the two 8 ohm jacks.

 

[bandit2013]

If you had two 16 ohm cabs, you can run both using the two 8 ohm output jacks. Not sure if there were changes over the years but my amp has two 8 ohm jacks and two 4 ohm jacks. Since each pair of jacks (one pair of 8, and one pair of 4) are live and always wired to the OT as it has two taps, one for 8 and the other for the 4. Using both 16 ohm loads plugged into both 8 ohm jacks will run the cabs in parallel resulting in a load impedance of 8 ohms.

Same would apply with two 8 ohm cabs, but you would use the two 4 ohm jacks.

Safe miss match would be one 16 ohm cab in one of the 8 ohm jacks, and one 8 ohm cab in one of the 4 ohm jacks.

I would not run two 8 ohm loads using both 8 ohm jacks as they are connected in parallel (internal) as the resulting load would be 4 ohms.

The manual pictograms for the speaker connections is too generic. Most Mesa Boogies will have one 8 ohm, one 16ohm (not on all models) and two 4 ohm jacks. Since the diagrams are generic (one serves all but not models specific) they do not address amplifiers that offer two 8 ohm jacks and two 4 ohm jacks as is the case with the full size Mark V. The diagram showing two 16 ohm loads connected to a parallel box then plugged into the 8 ohm jack would be the excact same thing connecting both 16 ohm cabs into each 8 ohm jack. Load box not required.

 

[BrownieD2W]

It looks like you guys are confirming what I thought, that connecting two 16 ohm cabs to the 8ohm Output jacks would be a "Correct Match".

Where as the 4ohm option would just be a "Safe-Mismatch" if you didn't have the pair of 8ohm Outputs as an option.

I was just a little perplexed as to why they didn't go ahead and make the effort in the guide to show your options when you have TWO 8ohm jacks and not just one, don't Triple and Dual Rec's have two 4ohm, two 8ohm, and one 16ohm Outputs? The Impedance Guide in the manual is more reflective of the Dual Calibers and some of the other smaller amps that don't have 2 sets of Outputs.

 

[BrownieD2W]

Thanks a lot for the input guys, this was kind of bugging me over the weekend and I wasn't willing to risk anything on my somewhat shaky understanding.

 

[bandit2013]

I have a Roadster, it is a dual rectifier. Amp does not have two 8 ohm jacks. It does however have one 16ohm, one 8 ohm and two 4 ohm jacks, same applies to the JP-2C. Either case, if you plan on using one 16 ohm cab and one 8 ohm cab many would think to plug in based on the ohms ratings on the jacks. Nope, have to do the 8 ohm 4 ohm thing. If you had two 16 ohm cabs, you would need a parallel box and use the 8 ohm.

The Mark V is the odd ball. The more I think about it, the Mark III and Mark IV had two 8 ohm jacks as well. One would think they could make a change to the common speaker impedance diagrams and include amps that have been made for the past 24 years.

At least you knew to ask before applying. Have loads of fun with your cabs. (pun intended)