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Mesa Boogie 400+ Cascading Gain?

Discussion in 'Amps and Cabs [BG]' started by slacker, Apr 2, 2002.


  1. slacker

    slacker

    Nov 27, 2001
    Portland Oregon
    The Mesa Boogie 400+ has (technically) two tube preamps, yes? One for each for inputs one and two. These preamps are then blended, and perhaps sent to a final driver stage.

    Is it possible to cascade these two channels, creating a pleasant overdrive situation?

    Anyone out there familiar with the Mesa Boogie "Dual Differential" D-180? How similar is the preamp section to that of the 400+? Could you mod a 400+ preamp into a D-180? Both are 4 tube preamps. The 400+ blends the channels, The D-180 cascades the channels.

    I know this guy with a soldering gun...
     
  2. Iused to split my signal and run both preamps in parralell. Pull out your "shift" knobs, set your EQ basically flat and what you end up with is the sweetest, punchiest tone. Playing through one preamp is thin and hollow in comparison; try it! Using this method you could also run your octave and filter fx in series, split your signal then drive any fuzz or distortion through just one of the preamps so you can blend to taste.
    I for one would love to get the 400+ preamp section in a single space rack......
     
  3. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    slacker, check yer email! Is it there yet?

    The 400+ is basically a fender showman with a huge power section and a few other bells and whistles. Flat is 0-10-0 bass-mid-treble.
    I have the schemo, and can mail it to ya if you want. I think it's a completely different animal than the D-180.

    I don't think it's possible to cascade the channels... if the boards were point to point, anything would be possible through mods... But they're not!

    I did have pretty good results running the Rick-O-sound of my 4001 into both channels.

    In the end though, i realized it's not mid-heavy or agressive sounding enough for me, and that's why it's now yours! :)
     
  4. You and I have chatted on this topic B4....;) So...if it's a Fender Showman circuit, how far is it in design from an Alembic F2B ? Are they very close do you think? The Alembic circuit is based on a Showman or was it a twin...? I would love to get a copy of your "schemo" if you had time? This is what Dusty from ZZtop does...plays through Showman preamps into power amps.
    Also, if it uses that mid-boost only thing, what freq. would I cut on my m-2000 to get it closer in style to the mid response of my old 400+?
    Thanks!
    Chris P.
    subharmonium@shaw.ca
     
  5. Hugh Jazz

    Hugh Jazz

    Sep 13, 2001
    Atlanta, GA
    ***Caution: Long Response Ahead***

    Hey Mad Subwoofer,

    I did some investigating on my own....

    Attached below is the graph of the Fender Showman circuit at "flat" (5/5/5). Assuming that the floor/flat level is -20 db, here's what I got for the EQ configurations tailored for the M-2000's graphic EQ:

    50 Hz = +2 dB
    80 Hz = +1 dB
    180 Hz = -3.5 dB
    300 Hz = -6.5 dB
    600 Hz = -5 dB
    1.2 kHz = 0 dB
    4 kHz = +5.5 dB
    6 kHz = +6 dB
    8 kHz = +6.5 dB

    Now here's the catch. This is assuming the EQ before the graphic is flat. Now I don't know if 5/5/5 on the bass/mid/treble knobs is actually flat, but I bet it's much closer than the 400+, which by NO MEANS is close. Plus you also have to consider that it's a graphic EQ and not a parametric, which means it won't be as smooth. That's where you'll need to do some tone shaping with the knobs and then use the graphic to fine tune the signal. Off the top of my head, I would probably put the bass at 5.5 to 6 (closer to 6), the treble a little over 6, and drop the mids down to 3 maybe 2, then use the graphic to cut the 300 and 600 Hz bands a notch (not too much since they've already been cut quite a bit to begin with).

    But there's one more thing! :p On the 400+, I noticed that you pulled the shift switches out. As far as I know, the bass shift moves the bass frequency to the low mids, and the high shift moves it down to the high mids. Sooooo.......that totally changes things around. Here's how I think I'd go about compensating for that:

    Graphically speaking (as in referring to the frequency chart), without the shift engaged, the bass frequency center seems to be around 25-30 Hz :)confused:). Yeah, sounds messed up, but when I boost or cut the bass while leaving everying else at 5 on the program, 20-30 Hz seems to be the focal range (the chart with the bass at 2, 5, and 10). I think the low shift would boost the center to the 80 Hz range. That in itself would boost frequences in the 50-200 Hz range, with most of the impact being the 100 Hz range (at least that's what my assumption is). The closer you get to 200 Hz, the smaller the boost as it is in the mid scoop range. The 370 Hz seems to be the focus of the mid scoop, so that'll remain cut.

    Now the highs appear to be pretty dang flat past 5-6 kHz. The evening out starts around 2.5-3 kHz. If you keep the Bass and Mids at 5 and boost the Highs up to 10, you can see how radically the frequency graph changes. Clearly the highs are the most powerful part of the EQ. From my interpretation, it seems as though the highs are shelved starting at around 3.5-4 kHz. If this is the case, then we can assume that this (or maybe 4-4.5 kHz) is the frequency center for the highs. Now according to the manual, the high shift is supposed to bring the center down to the "high midrange." This leads me to believe that the shifted center should be closer to 1-2 kHz. This will in effect boost everything from 370 Hz to 6 kHz, with the emphasis being in the 900 Hz-1 kHz area (I think...).

    So.....unless I'm way off, I'd imagine that the 5/5/5 + shifted settings will have the lows/low mids boosted by about 3 or 4 dB at 120 Hz, mid mids scooped by about -5 or -6 dB at 300-350 Hz, high mids boosted by about 3 dB at 900-1.5 kHz, and highs flat at around 4 or 5 dB. :eek::confused:

    On the M-2000, I'd do the basic mid knob cut, bass/treble knob boost on the tube side, while cutting mids a bit, but not too much on the SS side while boosting highs and the semi parametric bass at 100 Hz or a little below to give the huge bottom. I know that adding the SS side probably won't help get the tube sound, but it could help improve the overal tone and match the frequencies with those of the 400+. That, and you have to face the fact that even the tube side can't hold up on it's own to the 400+. Anyway, hopefully my theories and assumptions (the whole bunch of them!) are somewhat accurate or at least in the right direction. Again, I could be way off. But at least it's a start! ;) Let me know what you think and if it helps at all. (I don't have access to my amp.) For some reason, I feel that no matter how you tweak it, you won't get all that close (if at all) to the 400+ sound, even if you match the frequencies. But it could help improve your overall tone, which is what really matters!

    I think I'm done for now.... I need food and sleep.
     
  6. Hugh Jazz

    Hugh Jazz

    Sep 13, 2001
    Atlanta, GA
    The EQ settings I mentioned in the beginning of the previous post correspond to the following graph.

    "FLAT"

    [​IMG]
     
  7. Hugh Jazz

    Hugh Jazz

    Sep 13, 2001
    Atlanta, GA
    Bass at 2, then 5, then at 10

    [​IMG]
     
  8. Hugh Jazz

    Hugh Jazz

    Sep 13, 2001
    Atlanta, GA
    Bass and Mids at 5, Highs at 10

    [​IMG]
     
  9. Damn Hugh....you shouldn't be drinking all that coffee after dinner you know...:D
    Seriously tho'...this is one golden nugget of info. It's going to take me a while to absorb it...thanks for your effort. Rickenbackerman is convinced that flat on the 400+ mid knob is 10. I am going to try and assimilate this in the morning.....wow.
     
  10. Hugh Jazz

    Hugh Jazz

    Sep 13, 2001
    Atlanta, GA
    According to my tweaking of the graph, yes, true flat of the 400+ is with the settings at Bass = 0.4 (that's right, 0 is a little too little), Mid = 10, High = 0. When I mention "flat" in that behemoth post, I meant it as Bass, Mid, High all = 5.

    This is real flat, using the aforementioned settings (0.4/10/0):
    [​IMG]

    But yeah, I'm really anxious to see how that all turns out. It'll probably take a lot of tweaking and experimenting though since it's based on a ton of speculating and (educated) guessing/assumptions.

    And to think that I have a crap load of data to analyze for one of my class projects. Being a college student can really suck, especially when you get sidetracked so easily.

    Curses, man, curses.
     
  11. The old Mesa Boogie 400, the predecessor to the current 400+, had cascading gain stages and no graphic eq. It was also only 400 watts instead of the current 500watts.
     
  12. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    Yep Mad SW, we have chatted on this topic before... :)

    I tried to convince you before to go to duncanamps.com and download the tone stack simulator - the 400+ tone stack IS a fender stack, and flat IS 0-10-0. Hugh Jazz, I'm assuming you're getting those plots from the duncan simulator too?

    There is one thing you guys are missing though. All this discussion is about the tone stack only, which amounts to only a few components in the signal path. There are many other things that contribute, such as bypass caps and cathode resistors and whatnot... this is why channel 1 and channel 2 sound so different. And this is why the pull shift knobs have effects on the tone.

    If you guys want the schemo for the 400+, email Mesa, they will send it to you...
     
  13. What do you think I should say to them? Give me your schematics, I wanna build my own? Hmmm..maybe not. Tell them I have one that needs repair? What would you suggest?
    If I scoop out my 300hz slider on my M-2000 it should replicate the 400+ mid-curve, no?
    Thanks..
     
  14. Hugh Jazz

    Hugh Jazz

    Sep 13, 2001
    Atlanta, GA
     
  15. slacker

    slacker

    Nov 27, 2001
    Portland Oregon
    OUCH!

    My head hurts!

    Okay, first: Rickenbackerman, I have not recieved my amp yet. Damn you snail mail! Also I am between ISP's. Will give you my new email soon. I thought the 400 and 400+ had the same preamp. Only the D-180 had cascading gain. I could be wrong. Would a circuit board mod be *absolutely* out of the question? I know somone who could perform surgery.

    Second: Hugh Jazz, Thanks for all of the EQ info. I am a little dizzy. Much of this I already knew. Much is new.

    Third: Mad Subwoofer, I realize there are similarities between the Mesa 400+, Fender Dual Showman and Alembic. This is *exactly* why I brought the topic up. The Dual Showman *is* pretty much the same as a F2B. Still wondering if a mod would be possible. I had already considered running an F2B as an external preamp.
     
  16. Sooo.....I should just use an F2B??? That will get me something reminiscent of the 400+ preamp? Is this simple solution THE one? Could it be this easy?

    [​IMG]
     
  17. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    slacker - I'm pretty sure the 400 and 400+ have the same preamp...

    about the snail mail - Hmmm... I've been checking the usps tracking # and all I get is 'your package was recieved at the college park post office on march 26th'. ***?

    I don't see why you couldn't mod the 400+. Changing component values is one thing, but if you get into major surgery, you'd have to start cutting traces on the pcb. Do you really want to do that?
     
  18. Ok, so could I change the value of my 50hz slider on my M-2000 graphic to a 30 hz one? Blending the two preamps has just never sounded good to me and I already have a 50hz rotary knob...I need a 30 hz boost on my tube side.
     
  19. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    Are you sure you 'need' a 30 Hz slider? You can't even hear 30 Hz as much as you feel it. I'd bet you probably couldn't tell the difference between +6dB @30Hz and +6dB @50Hz anyway.

    If the 400+ sound is what you're after, you can get close with other options, but I'd think the best way to do it would be to just get a 400+?