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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Nagging noise problem with a 5F6-A Bassman

Discussion in 'Amp Central Station' started by gmm52, Nov 14, 2017.

  1. gmm52

    gmm52 Tele-Meister

    235
    Sep 23, 2016
    Southern Ontario
    I traded for a tweed Bassman 4x10 clone not long ago. In the last while I've posted several threads here related to it on one topic or another. I love the sound of this amp, and I'm enjoying the process of learning more about tube amp function by studying this amp in greater detail, but I am up against a nagging problem. I could just take it to a tech, and will if I can't solve it, but I'd like to continue trying for the time being. Here's the problem. The amp sounds stellar, with extremely sensitive touch and super clean chime, but it has a sympathetic buzz of some kind on low F# or G notes played on the 5th or 6th strings. It sounds like a mechanical buzz that comes through the speakers and might be coming from a tube with loose internal components, but I've switched out all the tubes, and it's still there. If I never had to play low F# or G notes, I'd swear it was the best amp ever, but I'm going to need all 12 notes moving forward.

    Any thoughts?
     

  2. corliss1

    corliss1 Tele-Afflicted Gold Supporter

    Sep 13, 2008
    Lansing, MI
    So, the trick with any troubleshooting is to isolate the problem.

    Do everything one at a time. Remove the upper panel and test (don't touch anything - it can kill you even when powered off and unplugged). Lower panel. Touch the handle while you play the note. Touch the little brass logo. Anything on there can rattle. Try holding different tubes while you play. If it sounds mechanical there just isn't an easy way around it except trying to remove or hold differnet parts while you play.
     

  3. Mr Ridesglide

    Mr Ridesglide Tele-Afflicted Silver Supporter

    Dec 11, 2009
    Bloomington, MN
    I would totally check the panels and see if problem goes away. If it doesn't, try the baffle board - Some have even heard the actual grill cloth making noise.
    nearly every tweed i have worked on or made has needed some cabinet adjustment to make the buzz stop. Sometimes it's a matter of moving the chassis forward about 1/8" to make sure it doesn't contact the rear panel. I've used the weather stripping with one side foam, the other tape before too to stop the contact and the madness.
    If it's not the cabinet - it could very well be a solder joint on V1 or V2 easy enough. Just reflow 'em all if you have to get in there.
    Do remember that there are lethal voltages inside that amp so DO NOT go in there if you're not familiar with the safety procedures required -
     

  4. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    Unplug the speakers and plug in a 4 ohm load, extension cab. Move it away from Bassman cab. Still hear buzzing?
     
    Chip.Lindsey likes this.

  5. gmm52

    gmm52 Tele-Meister

    235
    Sep 23, 2016
    Southern Ontario
    All good thoughts and ideas. Thanks. I'm hoping to have another go at it later tonight or tomorrow night.
     

  6. gmm52

    gmm52 Tele-Meister

    235
    Sep 23, 2016
    Southern Ontario
    So I might be making progress, but it's going slow. Using the inverse of Keithb7's idea, I plugged an external amp into each of the four speakers, one at a time, and got buzzes, not exactly the same but buzzes, but buzzes nonetheless. This at least revealed that the problem is not electromechanical, e.g., coming from a tube rattle or something similar. I then tapped on the speaker backs with a finger, and could detect a rattle that did not sound like it should be there. Took the amp out, and still had a rattle with a tap, so something purely mechanical at the amp is out as cause. Tapped on the baffle at the top and heard something suspicious. All screws were tight, and so I proceeded to take the speakers out. No rattle on tapping individual speakers. Tapped on the baffle with speakers out, and couldn't detect rattle, but then there was mass missing (the speakers) and that could have made a difference.

    Took the baffle out. To me, it seems like a flimsy connection, four screws, one at each corner of a relatively large and flexible panel, with the middle sections free to move against the cabinet. I am thinking of adding some braces, to better couple the baffle to the cabinet, but thought I better get some insight from others first.
     

  7. corliss1

    corliss1 Tele-Afflicted Gold Supporter

    Sep 13, 2008
    Lansing, MI
    All the tweed amps are built like that - hence the term "floating baffle"

    I'd poke around a bit more before modifying the amp at all.
     

  8. gmm52

    gmm52 Tele-Meister

    235
    Sep 23, 2016
    Southern Ontario
    Then what about putting washers on the four screws between the baffle and the cabinet, to perhaps change the way it sits? I found the baffle was very snug fitting. It seems to me that the movement back and forth at the midpoints could be a source of noise for a snug baffle.
     

  9. gmm52

    gmm52 Tele-Meister

    235
    Sep 23, 2016
    Southern Ontario
    I noticed that the grill cloth was frayed on one edge, and the little pieces could be buzzing against the cabinet with baffle movement, so I put some masking tape over the edges (not visible from the front) and reinstalled the baffle. The buzz is gone when tapping, and the baffle still floats. Won't be able to test it with power until tomorrow, but I think I've made an improvement, if not solved it entirely.
     
    Last edited: Nov 17, 2017
    corliss1 likes this.

  10. Old Tele Hack

    Old Tele Hack TDPRI Member Silver Supporter

    Age:
    50
    46
    Mar 31, 2017
    Virginia
    My Bassman rattled, but it was the back top panel vibrating against the chassis.
     

  11. gmm52

    gmm52 Tele-Meister

    235
    Sep 23, 2016
    Southern Ontario
    It appears I have solved the problem.
     

  12. corliss1

    corliss1 Tele-Afflicted Gold Supporter

    Sep 13, 2008
    Lansing, MI
    so it was some cloth vibrating on the sides of the baffle?
     

  13. gmm52

    gmm52 Tele-Meister

    235
    Sep 23, 2016
    Southern Ontario
    Yes, the frayed edge of the grill cloth (much more prominent on one edge, with the others being well cut and stapled). Rather that's my best guess, but given that I disassembled and reassembled virtually the whole amp, it seems possible that I also adjusted something else in the process. I could definitely hear a buzz when tapping the speaker backs (amp out) with a fingertip, and that buzz was no longer present after applying masking tape.
     

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