noise reduction mod for 400+ ??

Discussion in 'Amps and Cabs [BG]' started by dave_kts, Jan 8, 2009.

  1. dave_kts


    Jan 17, 2008
    waiting for my taxes so i can pick up my new old mesa 400+ from layaway, i've been looking around and a few times now i've seen some of these for sale claiming to have a noise reduction mod done to it. Anyone have any info on this? i'd like to know cause i had a little more hum in mine than id like when i was testing it, but also have reason to believe its time for new pre tubes in it. had some crackly- chewy sounds going on in input 2. haha chewy?
    any info on any kind of mods to this, let me know. I already plan on trying the P B G 12au7 driver swap, probably adjustable bias if it isnt already done to it.

    also, still seeking preamp tube recomendations and opinions. thanks
  2. anderbass


    Dec 20, 2005
    Phoenix. Az.
    I've never really had any hum issues with my 400+.

    I've also never heard of this mod so I googled it: and found a guy in the UK selling a 400+, stating he had this mod preformed by a tech named Dennis Marshall at a authorized Mesa repair facility called Emerson Williams.

    I've emailed the UK amp tech asking for info about this mod and I'm awaiting his reply.

    I did find 1 other reference to this 400+ mod on a current USA ebay auction, but this reference seems to simply have a few (copy and pasted) nearly word for word quotes from same UK sale amp mentioned above... :meh:
  3. anderbass


    Dec 20, 2005
    Phoenix. Az.
    Here's his reply. Sounds like he's probably a good tech but he isn't mentioning any mods...
    I'm thinking the "mod" term was simply added by the UK amp for sale guy to make his 400+ seem more desirable.

    Hi anderbass,

    Thanks for the enquiry. There are a few things I can do to the 400+.

    The main thing is to make sure the outputs tubes are correctly biased and balanced. I sometimes change the bias components to achieve this.

    The preamp stage can benefit from trying out different tubes depending on the required tone.

    A clean-out and service is always a good idea

    I would need to see the amp to be more specific.


    Dennis Marshall

    6 Main Street, Newmills, Fife, KY12 8SR

    Tel: +44(0)1383 881761


    From: anderbass
    Sent: 09 January 2009 04:03
    To: [email protected]
    Subject: Mesa 400+ Question


    I heard you perform a Noise reduction mod on the Mesa 400+ model and I'd be very interested in hearing a bit of info about this procedure.

    Thank you - anderbass
  4. EBBassMan

    EBBassMan Guest

    Mar 18, 2007
    Kew Gardens, New York
    The only time I ever had any noise issues at all with my 400+ was when one of the power tubes crapped out on me. Other than that it was always dead quiet.
  5. dave_kts


    Jan 17, 2008
    hmmm, seems like i shouldn't worry about it as this amp is usually noted being free of noise, and as it sits in the store now, it has 3 EH tubes sitting in with mesa power tubes. i'm sure its ready for a complete set of actuall matched tubes in the power section, and i've already got a small collection of 12ax7's and ux7's to try in her. I just cant stand the wait... need taxes now!

    and yeah, i saw the one on ebay. he claims it is a 1982 model, i thought the 400+ didnt come out till after that? He also says it has a 7 band eq, where in the pic it has 6. so it is an old model, but you're right about the copy and pasting...
  6. dave_kts


    Jan 17, 2008
    any thoughts on this set of power tubes?
    is the whole cyrogenically treated thing worth anything or make a difference?

    this set converts to $232 american. im sure i can find it for less, but does anyone suggest the cyrogenic treatment or is it just hype?
  7. dave_kts


    Jan 17, 2008
    nevermind on that last post, i read the thread on the cryo treatment. snake oil...
  8. anderbass


    Dec 20, 2005
    Phoenix. Az.
    Lots of guys wrongly assume they're 400+, 400 or D-180 series model is a 1982 cause thats the trademark date printed on many of the diferent years, rear panels. Ask your amp tech to look for some large handwritten dates he'll probably find on serveral of the large blue capacitors inside for a date of assembly on yours.

    I'm still not a 100% sure If Mesa can always date from its serial numbers or not... :confused:

    I went with a JJ/Eurotubes power tube set he sells for the 400+ in mine. Quite a few other 400+ guys on this forum seemed to really like the JJ set too. They've held up well and sound great in mine. I have a feeling the JJ's are probably one of the cleaner sounding powertube choices and for that reason alone, I'll probably try something else next time. I"m not sure what I'd try next but I've had an adjustable bias instaled in mine now and I'd like to get a bit more daring next time and see if some other quality powertubes might have a bit of diferent flavor.
  9. jimbilly


    Apr 19, 2006
    I've just been researching this too, I picked one up a week or so ago and it needs a few tubes, - some Mesa labeled tubes that are pretty widely ranging in mA draw at idle (20 to 45, most around 30). I think the Eurotubes guy knows Mesa and can supply a set that is pretty ideal for that amp, there's also a guy on ebay I've emailed that sells matching sets (up to 12) matched Sovtek 5881s for about $150, and from his email I'm satisfied that he knows what sort of current draw to match for in the 400+. You wouldn't want to get a set that's too 'cold', or too 'hot' for that amp. I've heard from a very reliable source that the Mesa labeled tubes are often poorly matched, so I'd go with Eurotubes or the ebay guy. I've got 6 that are within 2.5 mA (my tech tells me this is ideal), and I've got some more power tubes on the way that I hope to get a good match out of, if not, I'll end up going with the ebay guy for $150. My tech tells me that much more range of idle current than 2.5 mA (a poor bias match) will usually result in some noise.
    In case you're also wondering, the Sovtek 5881s are not a true 5881 (like the old small bottle TungSols that go in '50s amps), but a military 6L6GC equivalent, capable of handling high plate voltages just like the best 6L6s.
  10. dave_kts


    Jan 17, 2008
    what's the name of the ebay store selling those? $150 seems cheap as hell, almost too cheap
  11. anderbass


    Dec 20, 2005
    Phoenix. Az.
    I just wanted to let you guys know I've replied to the UK amp tech asking more specifically if he simply does a very throughal service or actually installs some sort of true mod in these amps. (I'm thinking he might use Psychos 12AU7 driver tube swap... although I was thinking an authorised Mesa repair dealer might not admit to any mods from the origanal design)
  12. dave_kts


    Jan 17, 2008
    OK, update on my amp...
    well i have it now and cured the crackling with a v1 tube change.
    The amp still has noise though, a 60 hz buzz constant, playing or not, increasing with the master and the gains, at very loud volumes it is almost intolerable in between songs. cant really notice while playing.
    buzzed louder with a pedal before the input. the pedal is quiet on my SS setup. the ground switch seemed to have no effect.
    It has older mesa power tubes with 3 EH 6l6 mixed in it
    I feel it also lacks a little of the very lows. 40 hz eq doesnt seem very useful.

    so i tried some preamp tube rolling...
    wound up with an RCA jcr? 12ax7 in the driver, and an EI yugo 12ax7 in V1, i think a JJ ecc83s in V2 and didnt do anything with V3

    I tried a couple 12au7's in the driver, but the noise was still there when you brought the volume up to the same level. the tone stack was more responsive, but i didnt stay with it. It was very quiet with an amparex 12au7 (well balanced) in the driver, but the high end was gone.

    What do you think, start with a fresh 12 pack of power tubes? maybe a grounding issue?

    V1 is extremely close to the output tranny. pretty much touching . are all the 400+ years like this?