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Mesa Bass 400 Question

LCbass2007

LCbass2007

Jan 21, 2007
143
164
Long Island, New York
#1
I have searched and not really found the answer yet. My buddy just got a Mesa 400 and wants to run 2 Ampeg SVT 8x10 off of it. I looked in the back and there is no 2Ohm input on the Mesa, just 2 4Ohm inputs and 2 8Ohm inputs. Is it possible two run 2 8x10 (4Ohms each) with one Mesa 400?

Thanks
 
#5
That is the manual for the 400+

Is that what you have LCbass...?

The Mesa 400+ has 2 ohm outputs so that would work - I'm not sure on the Mesa 400 though.

They are outputs by the way - sound comes OUT of them (into the cab).
 
#6
there are early and middle period mesa bass 400's with only an 8 ohm tap and a 4 ohm tap.
The late period Bass 400's have 8, 4 and 2 ohm taps.
So the short answer is that it is best bet to NOT run two 4 ohm loads off an amp that only has 8 ohm and 4 ohm outs.
To clarify, the 8 ohm and 4 ohm jack pairs are labeled as such meaning that the total impedance load across both jacks should be 8 ohms or 4 ohms.
If you plug in one 16 ohm cabinet to each 8 ohm jack you are at 8 ohms.
If you plug in one 8 ohm cab to each 4 ohm jack you are at 4 ohms.
If you plug two 4 ohm cabs you are at 2 ohms.
The amp was not designed to run 2 ohms, and seeing as it is an older amp that is VERY out of production, if you blow the output transformer it will be an expensive and difficult repair.
Okay all that beware jazz out of the way.
In my experience, and from what folks at Mesa and my amp tech tell me. It can feasibly do 2 ohms. Most 4 ohm cabinets are actually running from 2 ohms up to 16 ohms or higher at different frequencies. However, running at 2 ohms is dangerous and can damage the amp. It will do it no problem at low to medium volumes. But when you start really pounding it out (and if your buddy want's more loud than a Bass 400 into one 8x10!) that is when it will implode into a black hole of tube amp repair bills.
My tech's advice was to give up on the idea of runnign two 4 ohm cabs, and instead find two big old 8 ohm cabs.
Mesa made plenty of 8 ohm 2x15 and even 8x10 cabs. Get two of those.
4x15 is plenty loud.
 
#7
I am on my second Bass 400 and neither has 2-ohm capability. If the 2-ohm ones exist, they will be a high serial number, above 900.

If your buddy is trying to get more volume out of it (I mean 1 pushed 8x10 should be enough), upgrade the power section to 6550s/KT88's and run some sort of clean boost in the FX loop (I use a Sansamp BDDI on Line instead of Instrument level). It will give you the max in clean volume that is it capable of.
 
#8
The 2 ohm capable ones are kinda rare. I have only seen two with my own eyes. I think maybe there was a transitional period from the 400 to the 400+ when they were putting 400+ transformers on the 400? The ones that have all three taps have the exact same chassis as the ones that dont. They just tapped 2 extra holes for the 2 ohm jacks and put the label for them on top of the back panel.
I asked my tech to inquire with Mesa but no dice on getting retrofitted.
 
#9
Late 1988 into 1989 saw some 400's coming with 2ohm jacks.

I have an early 88 that doesn't, but I also have the original manual that says it is totally okay to plug two 4ohm cabs into the 4ohm jacks for a 2ohm load. I bought my amp in 1991 and called Mesa to verify the info, and I was told yes it's perfectly fine to do, and that a tube amp wants to see a balanced load (no 2.66 mixed loads from one 4 and one 8 ohm cab). So I have been doing just that, running 2ohm loads for over 20 years with this head.
I was told you can go lower (balanced load) impedance, you just cannot go higher impedance on a tube amp.

I have a Mesa 810 I got last year, and sometimes I run the 400 into it, and believe me I can't see the need for running two 810's!
 
#11
First, wow, I wouldn't want to be standing in front of two Ampeg 8x10s plugged into a 400. Accuweather may be tracking the mysteriously strong winds that appeared out of nowhere from the air being pushed from those speakers. :D

Second, is it possible to mod the 400 to run with a 2-ohm load, similar to how the Aguilar DB359 can be modded to accept a 2-ohm load?
 
#12
Caca de Kick said:
Late 1988 into 1989 saw some 400's coming with 2ohm jacks.

I have an early 88 that doesn't, but I also have the original manual that says it is totally okay to plug two 4ohm cabs into the 4ohm jacks for a 2ohm load. I bought my amp in 1991 and called Mesa to verify the info, and I was told yes it's perfectly fine to do, and that a tube amp wants to see a balanced load (no 2.66 mixed loads from one 4 and one 8 ohm cab). So I have been doing just that, running 2ohm loads for over 20 years with this head.
I was told you can go lower (balanced load) impedance, you just cannot go higher impedance on a tube amp.

I have a Mesa 810 I got last year, and sometimes I run the 400 into it, and believe me I can't see the need for running two 810's!
Click to expand...

From what I understand, it is possible to run a tube amp at a lower impedance that what it's rated for, but you are losing some power output when you do that. (Don't quote me on this though...don't my comment to be responsible for a blown transformer :hiding:).
 
#15
Thanks for the info. I have zero experience with the Mesa 400 (non plus), but it seems that everyone is confirming what I already thought; that it is not the best idea to be doing this and it may not have any positive impact on his power. He is new to bass gear (and bass in general), so he asked me, but I wanted to make sure.

I know my SVTII has two jacks with a 4/2 Ohm switch, which is what is was looking for (or something similar) on the Mesa.

Thanks all!!
 
#16
Calaverasgrande said:
there are early and middle period mesa bass 400's with only an 8 ohm tap and a 4 ohm tap.
The late period Bass 400's have 8, 4 and 2 ohm taps.
So the short answer is that it is best bet to NOT run two 4 ohm loads off an amp that only has 8 ohm and 4 ohm outs.
To clarify, the 8 ohm and 4 ohm jack pairs are labeled as such meaning that the total impedance load across both jacks should be 8 ohms or 4 ohms.
If you plug in one 16 ohm cabinet to each 8 ohm jack you are at 8 ohms.
If you plug in one 8 ohm cab to each 4 ohm jack you are at 4 ohms.
If you plug two 4 ohm cabs you are at 2 ohms.
The amp was not designed to run 2 ohms, and seeing as it is an older amp that is VERY out of production, if you blow the output transformer it will be an expensive and difficult repair.
Okay all that beware jazz out of the way.
In my experience, and from what folks at Mesa and my amp tech tell me. It can feasibly do 2 ohms. Most 4 ohm cabinets are actually running from 2 ohms up to 16 ohms or higher at different frequencies. However, running at 2 ohms is dangerous and can damage the amp. It will do it no problem at low to medium volumes. But when you start really pounding it out (and if your buddy want's more loud than a Bass 400 into one 8x10!) that is when it will implode into a black hole of tube amp repair bills.
My tech's advice was to give up on the idea of runnign two 4 ohm cabs, and instead find two big old 8 ohm cabs.
Mesa made plenty of 8 ohm 2x15 and even 8x10 cabs. Get two of those.
4x15 is plenty loud.
Click to expand...

well put, and thank you. Thats exactly what I was looking for.
 
#19
Caca de Kick said:
Late 1988 into 1989 saw some 400's coming with 2ohm jacks.

I have an early 88 that doesn't, but I also have the original manual that says it is totally okay to plug two 4ohm cabs into the 4ohm jacks for a 2ohm load. I bought my amp in 1991 and called Mesa to verify the info, and I was told yes it's perfectly fine to do, and that a tube amp wants to see a balanced load (no 2.66 mixed loads from one 4 and one 8 ohm cab). So I have been doing just that, running 2ohm loads for over 20 years with this head.
I was told you can go lower (balanced load) impedance, you just cannot go higher impedance on a tube amp.

I have a Mesa 810 I got last year, and sometimes I run the 400 into it, and believe me I can't see the need for running two 810's!
Click to expand...

I have got conflicting information on this. But the upshot seems to be, you can run two 4 ohm cabs if you arent gonna beat it hard, if you are going to be cranking it than stick to 4 ohms.
 

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