2 Cabs, 2 Impedences, 1 Tube Head

suraj · #1 05-20-2010, 04:09 AM

I have 2 cabs(2x12, 4x10) Which are 4ohms and 8ohms respectively. Now is it safe to run both together through a tube head..?? Mesa Bass 400

Like one on the 4ohm jack and one on the 8ohm jack..??
Since its a tube head, wont both get the same amount o watts and be safe to use..??

Ozzey · #2 05-20-2010, 04:26 AM

From my (very) limited knowledge on this, I know that a 4 + 8 ohm cab will give you a load of 2.67. Since the Mesa Bass 400 goes down to 2 ohms, your amp should be fine. But there are some things to check out about it for sure. This link seems to be quite relevant for your situation:
http://www.rickenbacker.com/forum_vi...e=2.67%20ohms?

Hope this helps.

Sartori · #3 05-20-2010, 04:44 AM

Wait, the 2x12 is 4 ohms and the 4x10 is 8 ohms? If I recall correctly, that means the 2x12 will be getting twice as much power as the 4x10. Sounds like a bit of a weird setup.

If your head is 2 ohm capable, it should work, though.

MAMMOTHvolume · #4 05-20-2010, 05:32 AM

get some matching cabs.

Moonbot · #5 05-20-2010, 05:42 AM

That is complicated
If your running the speakers in parallel then one 8 ohm cabinet and one 4 ohm cabinet will have a total impedance of 2.6 ohms.

If running in series then it will be total of 12 ohms.

I don't know anything about the Mesa 400 check out the manual and find out weather it will be running in series or parallel and what is the lowest impedance load the amp can run.

Bassmec · #6 05-20-2010, 05:56 AM

What you need to do to balance your rig is to connect the speakers in the two by 10 in series.
Check the crossover for the existence of LP filter on woofer bet it hasn't got one so it don't matter to the tweeter what impedance the bass drivers are but you might need to turn it down a bit more than normal.
The amp will be OK and the same power goes to each ten inch.

Sartori · #7 05-20-2010, 06:16 AM

Quote:

Originally Posted by Moonbot

That is complicated
If your running the speakers in parallel then one 8 ohm cabinet and one 4 ohm cabinet will have a total impedance of 2.6 ohms.

If running in series then it will be total of 12 ohms.

I don't know anything about the Mesa 400 check out the manual and find out weather it will be running in series or parallel and what is the lowest impedance load the amp can run.

The Mesa 400 is a regular tube amp. As far as I'm aware, it's in many ways similar to the D-180, which is what I use. In which case, it would be 2.67 ohms.

i_got_a_mohawk · #8 05-20-2010, 06:51 AM

You'll be running at 2.67 ohms.

Personally, I wouldn't do that. You'd probably be fine, but I wouldn't. I like to keep the impedance matched on a tube amp.

Quote:

Originally Posted by Bassmec

What you need to do to balance your rig is to connect the speakers in the two by 10 in series.
Check the crossover for the existence of LP filter on woofer bet it hasn't got one so it don't matter to the tweeter what impedance the bass drivers are but you might need to turn it down a bit more than normal.
The amp will be OK and the same power goes to each ten inch.

I'm guessing you mean the 2x12?

Considering it is probably two 8 ohm speakers in parallel to give the 4 ohm load. Wiring in series would give you 16 ohms. Which isn't going to help.

Sartori · #9 05-20-2010, 07:14 AM

Actually, what would a 16 ohm cab with an 8 ohm cab be? 5.something ohms? That would probably work. That would be above the minimum ohmage and would send twice as much power to the 4x10 as to the 2x12, which seems a bit better.

I must be not getting something.

**IvanMike** · #10 05-20-2010, 07:20 AM

NO, Stop. Don't.

Don't rewire your 212 just yet. Go read the ohms FAQ then go read info on TUBE amps, and contact MESA for their take on it.

For a solid state poweramp the rules are different than for a tube poweramp when it comes to impedance. Whatever you do, don't plug the 8 ohm cab into the 8 ohm output and the 4 ohm cab into the 4 ohm output at the same time. - Really.

Sartori · #11 05-20-2010, 07:48 AM

Indeed, those two outputs aren't supposed to be used at the same time on my D-180. The fact that it has two 8 ohm outputs is for plugging in two 16 ohm cabs (I suppose since they're common for guitar), or plugging in just one 8 ohm cab.

The two 4 ohm outputs are for two 8 ohm cabs or for one 4 ohm cab. I totally glossed over the part where he'd mentioned using the two different outputs at the same time.

i_got_a_mohawk · #12 05-20-2010, 07:50 AM

As has been said, you want to match the impedance, not just keep above it (as per with SS amps).

Sartori · #13 05-20-2010, 08:08 AM

Right, sorry for my uninformed posts.

OP, don't plug them into the 8 ohm and 4 ohm inputs, as now that I think of it, I'm pretty sure my D-180's manual says specifically not to do this, and it's fairly similar tot he 400, so probably a bad idea on that one, too.

suraj · #14 05-21-2010, 02:30 AM

So i guess its not safe..I actually bought a 410 8ohms and had plans to sell it for a 2x12 4ohms...i got some money and bought the 2x12 but now im having a hard time selling the 4x10...so i thought what if i can use it..!! I dont want to rewire any of the cabs..brand new and probably would be harder to sell..

So no1's really tried this..??

Sten · #15 05-21-2010, 03:01 AM

As already explained, this setup does not go really well with your tube amp - don't use them together. Even with solid state amp, where things are easier, your two cabs would mean that if you push lets say 300W into them:
4x10" gets 100W, which means 25W per driver
2x12" gets 200W, which means 100W per driver (4 times more!)

The 2x12" will be much louder, you will not hear your 4x10" at all. If you turn to a level you can hear the 4x10" you are already burning the speakers on 2x12". Go ahead and use the 2x12" (since the second cab will not make you much louder in this case) and keep trying to sell the 4x10".

Until you don't get rid of it, you can keep the 4x10" at another location so you don't need to drag cabinets between home and rehearsal space for example.

rodl2005 · #16 05-21-2010, 04:30 AM

+1 dont do it. Tube amps work (sort of) opposite to S.S. amps But contact Mesa 1st, then -probly best to- just sell & get another 8ohm cab

Bassmec · #17 05-21-2010, 04:55 AM

Quote:

Originally Posted by i_got_a_mohawk

You'll be running at 2.67 ohms.

Personally, I wouldn't do that. You'd probably be fine, but I wouldn't. I like to keep the impedance matched on a tube amp.

I'm guessing you mean the 2x12?

Considering it is probably two 8 ohm speakers in parallel to give the 4 ohm load. Wiring in series would give you 16 ohms. Which isn't going to help.

Why do you think that?
Adding a 2 X 12 cab Re-wired for sixteen ohms will get the same wattage to each voice coil in his rig. This is a good thing!.
And if he plugged it in the 4 ohm output of his amp with the other cab (daisy chained) in parallel with the 2 X 12 that gives a total load impedance of 5.3 ohms.
The result with a tube amp driven in this way is safe, not ideal but not too bad a match of ohms at all and not too bad a match of speaker output unless they have very different SPL's.
My work here is Done!

suraj · #18 05-21-2010, 06:01 AM

I think i'll just keep trying to sell my 4x10...keeping two cabsin two different locations so i dont have to move them is a killer idea

**IvanMike** · #19 05-21-2010, 06:46 AM

Running at 5.33 or 2.67 is theoretically possible with the switch set to 4 and 2 ohms respectively, but i'd run the scenario by mesa. If you're used to SS impedance amp "rules" tube amps can be a bit odd, It's actually worse to run them at higher impedances. Likewise, theoretically they are safe to a point in either direction, so with the 4 ohm switch on you could run 8 ohms or 2 ohms, but this is all theoretical.

Call Mesa, ask to speak to an amplifier tech.

i_got_a_mohawk · #20 05-21-2010, 07:17 AM

Quote:

Originally Posted by Bassmec

Why do you think that?
Adding a 2 X 12 cab Re-wired for sixteen ohms will get the same wattage to each voice coil in his rig. This is a good thing!.
And if he plugged it in the 4 ohm output of his amp with the other cab (daisy chained) in parallel with the 2 X 12 that gives a total load impedance of 5.3 ohms.
The result with a tube amp driven in this way is safe, not ideal but not too bad a match of ohms at all and not too bad a match of speaker output unless they have very different SPL's.
My work here is Done!

Why do you want each speaker to get the same power? The 12 inch speakers will be able to push more air than the 10s and both speaker types will have different sensitivities.

Also, I'm going by what I would do, and I wouldn't run a tube amp at 5.3ohms.