Mesa 400+ impedance question

Discussion in 'Amps and Cabs [BG]' started by ariff, Dec 10, 2012.

  1. ariff


    Nov 28, 2007
    Lawrence KS
    So the 400+ has two output taps on the back marked 2 ohm, two marked 4 ohm and two marked 8 ohm the idea here is it you are running 2- 4 ohm cabs you hook them to the 2 ohm taps to present the amp with a 2 ohm load likewise with two 8 ohm cabs run hook them to the 4 ohm taps. What should I use if I am running a 8 ohm and 4 ohm cab together which total around 2.6 ohms?
  2. What are the cabs? I wouldn't recommend running different impedance cabs in most cases
  3. ariff


    Nov 28, 2007
    Lawrence KS
    2x10 avatar and 1x15 avatar.. 2x10 is 8 ohms and the 1x15 is 4 ohm. Been running these cabs with several different heads (Peavey and Carvin) without any issues ever. Just picked up the 400+ on CL a few weeks ago which will mainly be used with my Power House 8x10.. But for smaller gigs which require us to lug gear up stairs I like to use the 2x10 and 1x15..
  4. You're onto it.
    With tubes it's generally better to run under the rated tap impedance than over it. In this case 2.6 is so close to 2 it probably wouldn't stress things too much but tough call to make.
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  6. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    If the 400+ is not fixed variable bias modded?, its such a cold running amp on its tube set, it would do no harm to run it at 2.6 ohms on the two ohm tap and I am usually a bit of a stickler for not messing with tube amp output tap/speaker matching impedances.:bassist:
  7. ariff


    Nov 28, 2007
    Lawrence KS
    OK good to know.. This is my first tube amp so I am still learning about them. I actually think I have a 8 ohm 15" speaker in another cab I might just switch them out to be safe. And no the amp has no bias mods done to it. It is stock fixed bias..
  8. IIRC There was mention of your situation in the manual, which the last I knew was still available for download on Mesa's web site.
  9. Brookdalebass

    Brookdalebass Supporting Member

    Jan 15, 2009
    Northern CA
    Yikes. Now I'm confused. I've been running my 400+ with two 8 ohm MarkBass cabs (4x10 and 2x10). I plug one cab into the 4 ohm output of the Mesa and take a Speakon from that cab to the other...two 8-ohm cabs in parallel...isn't that presenting the amp with 4 ohms?
  10. Yes... so why the confusion?
  11. Brookdalebass

    Brookdalebass Supporting Member

    Jan 15, 2009
    Northern CA
    Thanks, Nicoli...ariff's original post kind of made me think I was doing something 400+ sounds great and is actually louder and much meatier than my MarkBass Tube 800 head through the same cabs.

    I started my bass playing career with tube amps but switched to solid state...then hybrids: Hartke, Ampeg, Eden, Aguilar, Mesa...always felt something was missing. Got the Mesa 400+ a few months ago and found out what that missing link was.
  12. turdferguson


    Nov 11, 2014
    so he 400+ has 3 four ohm taps, if i recall correctly. it looks like the one on the left is for running one 4 ohm cabinet and the two on the right are for running two 4 ohm cabinets in parallel? when i look at it I'm confused. i rarely if ever have the need or the room to run two cabinets off the amp, but i'd like to be sure that if and when i do, I'm hooking everything up correctly / safely.....?
  13. ThisBass


    Aug 29, 2012
    You'll be fine with
    8 Ohm cab => 4 Ohm tap
    4 Ohm cab => 2 Ohm tap

    In this case the 400+ expects 2.7 Ohm total load.
    Impdance then is matched fine