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Mesa 400+ DI out VOlume mod??

Discussion in 'Amps and Cabs [BG]' started by mactac, Mar 9, 2006.


  1. mactac

    mactac Supporting Member

    Nov 28, 2005
    Victoria, BC, Canada
    OK, so the mesa 400+ has an xlr DI out. The problem is, the stupid engineers who designed this amp hooked it up to the master volume knob. this means 2 things:

    1. if you are using it at a gig, every time you adjust your master, you also adjust the volume to the board. bad
    2. you can't record with the DI without having your master volume turned up.

    the slave also sort of works for a DI, but at least on my amp, you can't run it with the master at 0. (it sounds all distorted for some reason...does anyone else have this problem?). also, i'd prefer to use the xlr. (speaking of which, does anyone know any specific technical differences between the slave out & DI out?)

    anyways, is there some sort of mod to disconnect the master volume from the DI?
     
  2. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    The reason Mesa put the XLR after the output tubes is to get the added tone. The slave out isn't intended for recording and is a bit dirtier, but would work for a mixer or another poweramp live. It is annoying that you have to turn up, but it does add tone. I have been thinking about modding my 400+ so that you can turn individual tubes off and get awesome tone without turning up loud. If you are looking for a preamp (gain) out, try the FX loops.
     
  3. mactac

    mactac Supporting Member

    Nov 28, 2005
    Victoria, BC, Canada
    what do you mean it comes "after the output tubes"....?

    if it came after the output tubes, it would be putting out MUCH higher voltage than line level.

    where exactly is the DI ?
     
  4. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    Im no engineer, but its connected to the speaker tap somehow.
     
  5. mactac

    mactac Supporting Member

    Nov 28, 2005
    Victoria, BC, Canada
  6. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    I have the schematics for the 400 and 400+ . . . . so this is fact, not speculation . . . . .

    On the 400/400+, signal is taken from the 8 ohm output transformer tap and then run through a voltage divider (to reduce the level to that appropriate for a line out) which feeds the DI output. As others have said, this is on the backend of the amp, so any "coloration" of the sound, including output tube overdrive distortion, will be in the DI output, which enables you to get a much more accurate tone on the DI output than if it were taken pre-final amp stage. The perceived "down side" is that since it is taken off the output transformer, every control that affects your sound to your speaker also affects the DI out.

    - Tim
     
  7. mactac

    mactac Supporting Member

    Nov 28, 2005
    Victoria, BC, Canada
    is there anyone who actually knows how this amp works who can chime in?

    also, how does the slave out differ from the DI (& why is it "dirtier")?

    thanks!


    AHA... just read the post above (wrote this at the same time) makes sense!

    how about that slave?
     
  8. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    The slave may be taken from the preamp stage. I dunno really where its from. But you can get better luck for a 1/4 in DI with the FX out anyway. I think that the dirt may be from the volume control on it.
     
  9. mactac

    mactac Supporting Member

    Nov 28, 2005
    Victoria, BC, Canada
    thanks...
    what does this mean : "for a 1/4 in DI "

    1/4 DI? i don't understand

    also, doesn't the fx out cut out the signal going to the poweramp?
     
  10. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY

    Yes, but if you're using a 1/4" DI in the effects loop, you can take a 1/4" back out of the DI and back into the amp.
     
  11. mactac

    mactac Supporting Member

    Nov 28, 2005
    Victoria, BC, Canada
    "Yes, but if you're using a 1/4" DI in the effects loop, you can take a 1/4" back out of the DI and back into the amp.
    "

    i can't see how this would be good. you'd be putting post-poweramp signal back into the amp pre-poweramp.

    this would be a Massive no-no...no?
     
  12. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    I think what he is saying is to take the effect send, and send it to your DI box. Then take the loop through from that, and send it back to the effects return. The XLR DI is never used. This would give you the tone of the preamp and eq, but none of any distortion or color that you are getting from the output tubes. To me, that kinda defeats the purpose of having a tube amp, since a lot of the tube sound we know and love comes from the output stage. To each their own, I guess . . . . .

    And for that matter, since on any amp, volume changes on the guitar, preamp input, etc. all show up at the DI, I don't get why this is such a big deal. How many times do you really change the master on your amp when you play anyhow?

    - Tim
     
  13. mactac

    mactac Supporting Member

    Nov 28, 2005
    Victoria, BC, Canada
    ahh... got it

    thanks!
     
  14. So, can you pull the tubes on the 400 like you can on the 400+ for optimal tone/volume settings?
     
  15. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY

    +1


    In my time gigging with my 400+ I haven't had any soundguys complain about the tone or noise offa the XLR.

    I have had a couple of guys complain that the signal was too hot, though. I've noticed each time someone had a problem with it, they were non-pro, weekend warrior type of soundguys who maybe didn't have much experience or training at the board. Usually I get 'Great signal from the bass!'.

    I am very hesitant to use a direct box before my amp. I much prefer the colored sound post EQ and in this case, post power tubes...I want the sound man to have as close to my stage tone as possible to make less work for him.
     
  16. mactac

    mactac Supporting Member

    Nov 28, 2005
    Victoria, BC, Canada
    "How many times do you really change the master on your amp when you play anyhow?
    "

    when i'm recording especially.
     
  17. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    Do you have any new thoughts, or info, about this amp-mod? (And/or), about any sonic improvment, this amp might receve, with bias pots instaled?
     
  18. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    "Mesa" tubes are specifically selected to run at a certain bias that the 400+ is always set at. They are just other brand tubes selected and rebranded. You can better select a bias for a different tube with a pot. There was a thread a week or so back I think on this. Do a search.