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Attention : Mesa 400+ Owners

Discussion in 'Amps and Cabs [BG]' started by top028, Dec 12, 2014.

  1. Dec 12, 2014 #1
    top028

    top028

    Dec 14, 1999
    Lancaster, PA
    I have stumbled on the key to unlocking great sound of my amp. I was feeling like for 300 watts it felt a bit soggy. I cut out the parallel effects mix potentiometer. I dare not leave the house without a small patch cord, but THE TONE! It took just a few min. Don't mess around inside if your not a confident tinkerer, but be encouraged that its a simple process that only requires a few snips. The 12au7 swap in tube 4 on the left (many posts about this one), is also essential and can be done by anyone with a screw drive and patience.
     
  2. Dec 13, 2014 #2
    anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    Was your Effects Blend pot defective, or do you think all D-180, 400 and 400+ amps would benefit from this mod?
     
  3. Dec 13, 2014 #3
    mpdd

    mpdd neoconceptualist

    Mar 24, 2010
    LA
    hmmm
     
  4. Dec 13, 2014 #4
    waltdogg

    waltdogg

    May 24, 2014
    This has me thinking about mine now... Wish I had it still to try this.
     
    dukeisdog likes this.
  5. Dec 13, 2014 #5
    top028

    top028

    Dec 14, 1999
    Lancaster, PA
    The pot itself worked just fine, or as fine as the design. I may be crazy, but it seemed like it was loading the signal the way I can plug my bass into a stereo or something else with low impedance. Its wired sort of like a reverb blend knob, but the effects loop in the 400+ doesn't have a "reverb recovery stage" I guess that may effect how it works. I only use the effects loop for a compressor that reverses the phase for my upright. I tried using the blend with a fuzz pedal and micro bass synth, but I only liked both extremes. Maybe the 1 meg pot in the 400 sounds better than the 5k in the 400+. I tried a bunch of mods to open up the bandwidth of the amp, and this was my last ditch. What a difference! like taking the wool blanket off.
     
  6. Dec 13, 2014 #6
    Razman

    Razman

    Feb 10, 2005
    Orange Park, FL
    Faulty pot possibly? I wonder if running a short cord between the send and return would emulate this. that's what the GK guys do when they have problems with their 400rb and 800rb.
     
  7. Dec 14, 2014 #7
    top028

    top028

    Dec 14, 1999
    Lancaster, PA
    I did try that first, but it wasn't the same. The biggest difference is at low settings 1-4 on the master vol. I really think its the 5K pot. I may try to put a 1 meg pot in as in the previous designs, but I don't have much use for the mix.
     
  8. Dec 14, 2014 #8
    Razman

    Razman

    Feb 10, 2005
    Orange Park, FL
    Hmmm, my 400 isn't soggy at all, it's a hairy beast I don't know if I'd benefit from pulling out that pot. I did try a 12au7 and it significantly reduced the gain, so I went with a hotter 12ax7.
     
  9. Dec 15, 2014 #9
    anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    When you cut out the blend pot, did you jumper the amps 2 connections together, or just simply disconnect the pot?

    MesaBoogieBass400Page5FXloop-Graphi.jpg
     
  10. Dec 15, 2014 #10
    beans-on-toast

    beans-on-toast

    Aug 7, 2008
    It is important with these amps to clean the EQ footswitch jack shunt contact with a product like DeOxit. The shunt is a switch that the signal to ground runs through and the contact will oxidize with time and lead to a deteriorated ground connection. This can make the signal passing through the graphic EQ muddy.

    A lot of people don't use the EQ footswitch and tend to forget about maintenance on the jack. Keeping that jack clean and you'll have a better sounding amp.
     
    LiquidMidnight likes this.
  11. Dec 15, 2014 #11
    TMARK

    TMARK

    Jan 10, 2012
    Richmond VA
    Best mod I had done to mine was adding adjustable bias.
     
  12. Dec 15, 2014 #12
    chaosMK

    chaosMK

    May 26, 2005
    Albuquerque, NM
    Too much hip thrust
    Is your theory that the FX loop is slowing the amp down?

    I run a Sansamp BDDI at Line level blended in my FX loop. I find that running at Line level gives me a great clean boost and quite a bit more headroom. I suppose it's slamming the power section a lot harder with out preamp gain.

    Note: GEQ in these heads comes after the FX Loop.
     
  13. Dec 15, 2014 #13
    top028

    top028

    Dec 14, 1999
    Lancaster, PA
    Thanks beans on toast! I will hose it down next time I get inside. Its certainly a hairy beast cranked up! Its hard to tame the gain. My goal with this amp is to have a higher power bassman 100, maybe I should have just got a fender, but I like the size and weight of this guy and the bulletproof construction is awesome. It just seemed that i couldn't get the right balance of volume and breakup. But now it seems that i got it. Its clean when I want it, the treble is clear and the low mids have more definition. Not that it really matters, I realize now that I was completely mistaken about 5K pot it IS 1meg like the older models.

    I actually unsoldered the pot from the circuit in case i wanted to hook it back up. To patch the preamp and the power amp together, I use a really short patch cord. I use a compressor to tame my double bass and run it in the loop.