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After PsychoBassGuy's 400+ 12AU7 mod, what have your experiences been?

Discussion in 'Amps and Cabs [BG]' started by bigbajo60, Sep 13, 2008.

  1. bigbajo60


    Nov 7, 2003
    Laredo, Texas
    I've just come through the first couple of gigs with my Mesa 400+ post 12AU7 mod... and I've gotta say that the improvement in headroom and EQ flexibility is very nice. I can see that this wouldn't necessarily be a mod for everyone, but I think I'm one of the ones who it was meant for. However, what I can't say is that I've settled on any particular new setting yet.

    Right now, I've come through these first gigs with the Master dimed (something I couldn't do before the mod)... with Input 1 anywhere from 3 to 6, depending on the venue. As far as the EQ, treble is set at 2, bass at 3 (pull shift) and mids at 10 (the graphic is only switched in when I use my Rickenbacker...). I wonder if the 10-2-2 (Mid-Bass-Treb) "flat" settings still apply post mod?

    I'm still debating whether I've arrived at a sound that I can really dig (the rest of the band says it sounds solid!). I am getting really good punch and clarity with those settings, so I know I'm close.

    How about you? After the 12AU7 mod, where have the settings on your 400+ ended up at? Also, are any of you doubting whether the 10-2-2 (M-B-T) setting still equals "flat" with this mod?
  2. fireincairo


    Jul 8, 2008
    I didn't use 12au7 tubes, but I did put 12at7's in both V1 and V2 of my Peavey Butcher amp. It totally cleaned up the tone of the amp and I can now crank both pre and post volumes all the way with no overdrive whatsoever. It's just pure headroom.

    Like was noted in Psycho's original thread, without the gain you lose a bit of volume. However, the tones are quite excellent, and my amp is still pretty darn loud. I have not used this rig in a practice or gig setting yet, so I can't really speak to whether or not it will be an issue. I have a feeling that since I only have a 120 watt head the band situation I get going will have to practice kinda quiet if possible. That's not a bad thing, there really is no need to practice full bore with a band. That's nothing but a recipe for tinnitus.

    Also, I think it should be noted that changing preamp tubes can subtly shape the EQ of your amp. One preamp tube can add more lows, while another accentuates the mids, and still others accentuate the highs. This is what makes tube tweaking so fun because you can really fine tune an amp to your taste.
  3. jgsbass


    May 28, 2003
    Floral Park, NY
    I recently swapped a 12au7 in place for a 12ax7 in a Presonus Tube pre and the lower gain is a godsend. I can use more tube sound now and its got a wider sweet spot for dialing in the right volume. I use the pre in front of a Linden eq so I don't miss the gain but I enjoy a cleaner signal that seems tubier.
  4. pgnbstrd

    pgnbstrd Supporting Member

    Aug 14, 2001
    Metro Detroit Michigan
    I'm playing an ampeg svt-4pro, do you think swapping an 12au7 in place of one of the 12ax7( I'm assuming I'd swap the farthest from the left) would help with getting a bit more headroom with out grit or clipping?
  5. fireincairo


    Jul 8, 2008
    Yes, without a doubt. I would invest in a few different preamp tubes and test them out to find which one suits your ear best. I've scavenged a ton of old tubes from old guitar heads over the years, but you can find NOS tubes on ebay. You can buy from good online dealers like www.dougstubes.com or www.kcanostubes.com

    Both of those vendors have good reputations online. Dougstubes actually has ratings for how much gain his power tubes have, which is a nice option for a bassist looking for the least amount of distortion.
  6. rayzak


    Jan 13, 2001
    Louisville, KY
    I'm reviving this thread to hear more of your experiences with this mod. I read about the tube swap and am seriously contemplating ordering a 12au7 tube to do this. Would JJ be a good, inexpensive brand to use?
  7. I love the JJ12ax7s for bass, not sure about their other 12xx7 brands. The 12ax7 has a really good balanced sound with lots of bass.

    Keep in mind that the 12ax7 is a high gain tube, with a factor of 100. 12au7 is a low gain tube at 19. 12at7 is middle of the road at 60. I would honestly start with a 12at7 because going from a gain factor of 100 (ax7) to 19 (au7) is a huge drop, unless a drastic reduction in gain is desired, like if your amp sounds like Cliff Burton's. That drop in gain is not only going to reduce distortion, but also output as mentioned above. You might notice a really big loss in overall volume with a 12au7.

    There's a good explanation of it here: http://thetubestore.com/gainfactor.html
  8. This was covered in the thread. A 12AT7 is NOT a positive alternative to the 12AU7 for the amp. And for the record, the amp's maximum volume is not compromised AT ALL. The "volume loss" is simply a gain restructuring and can easily be compensated for with increased input gain and master volume settings.
  9. relax dude, the 400+ wasn't the only amp in question here for the mod. I was referring to any amp switching preamp tubes in general. I tried a 12au7 in a peavey and it was much quieter with a very reduced output. Just trying to save someone $15 and a trip to the store.

    I didn't read the original thread obviously, just trying to give some advice. I'd appreciate it if you didn't treat me like i'm some sort of dufus because i haven't read every single thread.
  10. In the thread, a troll kept insisting that a 12AT7 would work better along with a bunch of other stuff that was nonsense. Considering this thread asks about the results of that one, it's not out of line to ask that it was consulted.
  11. Tony Gray

    Tony Gray

    Mar 6, 2006
    I think the 400+ was the only amp in question here.
    Since you obviously didn't read the thread, you didn't really know what you were talking about.
  12. bigbajo60


    Nov 7, 2003
    Laredo, Texas
    Since I'm the OP on this thread, I'd like to make one last contribution to the topic.

    The tube swap made the 400+ the amp I'd always wanted. My rig ended up being closer to a "bassman on steroids" than I ever could've imagined. And that was the tone I'd been after for more than 20 years. :bassist:

    Unfortunately, a "perfect storm" of several external considerations have now forced me to downsize... so...

    So long dream rig. :bawl:

    On the plus side, the new Walkabout rig rawks! :D
  13. Did you read pgnbstrd's post? I'm not a jerk but i get po'd when people question my intelligence like that.
  14. I feel ya... i gotta get rid of my SUV and downsize to a half stack live... no more pulling a trailer either :bawl:

    On the plus side, the one guitarist has an 89 lincoln town car... if we can jam some of our stuff in there we will be travelling in style!
  15. rayzak


    Jan 13, 2001
    Louisville, KY
    Didn't mean to start a fuss fellas:cool:
    I'm getting excited about the "swap". I just ordered a J/J 12au7 for it(Boogie 400+)
    Another quick question, if you don't mind. When using this mod, do most of you use Input 2? I know a lot of guys here use both inputs, but for those who don't. My Sadowsky's output is so loud, I usually really prefer it on Input 1. Would this mod allow me to use Input 2 with better results?
  16. does that mean you are selling the 400+......id like to look at that
  17. K-Funk


    Sep 24, 2007
    Auburn Hills, MI
    For a while I was going without the mod on my Bass 400 because of the decreased volume, but about a week ago I decided to give it another shot. After some re-tweaking of the input and master volumes, I now have a much better tone and plenty of useable volume.
  18. bigbajo60


    Nov 7, 2003
    Laredo, Texas
  19. I use both, but probably for the opposite reasons of most. My basses are mostly passive and I play very hard, so signal level is not an issue with me. I use the different inputs for different tone. With the Input 1, it gives a more mellow tone for passive basses at the expense of mids: big old Bassman, but if I need a more aggressive sound, I use Input 2. You'll have to play around with their gains, the master volume and your bass's output. Remember that with an active bass like your Sadowsky, you don't need to run your bass's volume at full to keep from losing tone.

    Absolutely! You'll find you now have a much more useable means of dirtying up the amp should you desire to.

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