Power Transformer mechanical buzz/hum

Discussion in 'Shock Brother's DIY Amps' started by Linkjr, May 4, 2019.

  1. Linkjr

    Linkjr Tele-Meister

    Age:
    50
    Posts:
    116
    Joined:
    Aug 16, 2017
    Location:
    Uk
    Hi Guys,

    My champ was playing perfectly then got an intermittent hum/ buzz which I initially thought was a ground hum, I have checked all components including the back of the board but can't find anything suspect.

    I removed the chassis and narrowed it down to a mechanical buzz hum from the power transformer which is intermittent.

    Is this indicative of a problem in the circuit or a type of transformer failure?
     
  2. Greg_L

    Greg_L Tele-Holic

    Posts:
    969
    Joined:
    Jun 27, 2018
    Location:
    Texas
    Have you tried tightening the mounting and lamination bolts?
     
    Linkjr, FrontPU and Wally like this.
  3. dan40

    dan40 Tele-Afflicted

    Posts:
    1,539
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    Some PT's do hum when in use. I had a Marshall DSL 50 that had a noisy PT and it ran fine for many years. I do agree with Greg L though, check all mounting and lamination bolts first. Also take a close look at the power tube. A bad tube will draw excessive current and cause the amp to hum loudly.
     
    FrontPU, Chiogtr4x and Wally like this.
  4. sds1

    sds1 Tele-Afflicted

    Age:
    43
    Posts:
    1,176
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Is this a vintage transformer or? Just curious how old it is.
     
    telemnemonics likes this.
  5. schmee

    schmee Poster Extraordinaire Silver Supporter

    Posts:
    9,446
    Joined:
    Jun 2, 2003
    Location:
    northwest
    Rectifier maybe....
     
  6. Wally

    Wally Telefied Ad Free Member

    Posts:
    34,653
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    +1 on checking the nuts, bolts and screws. I have been around vibrating PT’s that exhibited no other issues, but Inhave never seen one that had an intermittent problem.
     
  7. Bob Womack

    Bob Womack Tele-Afflicted

    Posts:
    1,113
    Joined:
    May 28, 2016
    Location:
    Between Clever and Stupid
    I've got an Avalon VT-737 tube preamp in the turret rack to my left in the studio that has physical power transformer hum that comes and goes. There's a multi-rack distribution amp rack behind me that has the same problem. In rack units it is often amplified by the business of directly bolting the rack units to your studio rack. I've put in rubber or paper shims to mitigate the noise. My Marshall amp has worked fine since I bought it new in 1996 though it has physical power transformer hum.

    Tranny crap happens. :D

    Bob
     
  8. Linkjr

    Linkjr Tele-Meister

    Age:
    50
    Posts:
    116
    Joined:
    Aug 16, 2017
    Location:
    Uk
    Thanks for the response guys, I have tightened all the bolts on the PT, have the chassis out and doing some more testing, it's fairly new less than 2 years old , I saw an arc on pin 8 of the 5y3 but happened after the intermittent buzzing started I resoldered and changed the tube but buzzing is still intermittent
    It's strange the amp still works as it did before but the buzzing with tha amp out of the chassis is really loud
     
  9. Greg_L

    Greg_L Tele-Holic

    Posts:
    969
    Joined:
    Jun 27, 2018
    Location:
    Texas
    With the amp guts exposed it's subject to all kinds of interference. It's not unusual for an amp to buzz and be noisy when it's out of it's cabinet.
     
  10. Linkjr

    Linkjr Tele-Meister

    Age:
    50
    Posts:
    116
    Joined:
    Aug 16, 2017
    Location:
    Uk
    True Greg_L but this is a recent thing my amp was previously dead quiet, even chassis out. In troubleshooting I turned off when I heard no buzz then turned back on and had it buzz - not switching or changing anything in the environment.
     
  11. sds1

    sds1 Tele-Afflicted

    Age:
    43
    Posts:
    1,176
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Voltages are the same with and without the buzzing?
     
  12. Linkjr

    Linkjr Tele-Meister

    Age:
    50
    Posts:
    116
    Joined:
    Aug 16, 2017
    Location:
    Uk
    Just an update the intermittent issue is now permanent :(
     
  13. Greg_L

    Greg_L Tele-Holic

    Posts:
    969
    Joined:
    Jun 27, 2018
    Location:
    Texas
    In a way, that's good. A consistent problem is easier to track down than an intermittent problem.
     
  14. Linkjr

    Linkjr Tele-Meister

    Age:
    50
    Posts:
    116
    Joined:
    Aug 16, 2017
    Location:
    Uk
    Yes that's the best way to look at it, every cloud etc

    Ok! I made some progress I got rid of the buzz by switching off my cathode bypass cap on switch, the problem is the volume seems to be abnormally low with this off now.
     
  15. Chiogtr4x

    Chiogtr4x Poster Extraordinaire

    Posts:
    5,970
    Joined:
    Mar 29, 2007
    Location:
    Manassas Park, VA

    Related topic /questions, please
    ( BTW , I'm a good player but NOT a tech-type, but still try to learn, if I can ever really retain any info! )

    I just took my 1999 Blues Jr. ( which I really have used for a thousand gigs, I bet) to my amp tech buddy, as it had literally died right before a big show( light ON, tubes glowing, NO sound)

    He always does initial trouble shooting with customer there ( me!) for 15-20 min., then I leave amp for about a week, turnaround time.
    tThis time after checking ( with multimeter and scope, he also tested tubes) he determined that the power Transformer died- not common in BJ's he said, but my amp has a lot of use...

    Anyway, can someone ( in simple terms) explain how a PT works/ what it doe, and what 'stops happening' that makes one go bad? Just curious...
    Thanks!
     
  16. Obelisk

    Obelisk Tele-Afflicted

    Posts:
    1,345
    Joined:
    Apr 1, 2013
    Location:
    NW USA
    I had a 67 Traynor YBA-1 that had a power transformer that would audibly hum if the amp volume was turned down. Once I was playing, I never noticed the sound. I was told a by a tech that the sound is caused by the hardening of the epoxy that holds the laminations together. It wasn't totally annoying, but it was an audible hum that had nothing to do with anything wrong in the circuit or the tubes. These were the older Canadian made Hammond transformers. I still own 4 other Traynor amps that do not exhibit the same phenomena. I have also had a Gibson GA-79 that had a similar problem.
     
  17. sds1

    sds1 Tele-Afflicted

    Age:
    43
    Posts:
    1,176
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Sure I'll start. A transformer is a long piece of wire wrapped around a core.

    Some ways a wire can stop working as intended: 1) it breaks, 2) it touches something it shouldn't

    Maybe I oversimplified it, I dunno. :)
     
    Chiogtr4x likes this.
  18. sds1

    sds1 Tele-Afflicted

    Age:
    43
    Posts:
    1,176
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Interesting discovery!

    The lower gain without the bypass cap is expected, a cathode bypass cap by nature increases the gain of the stage it's associated with.

    By the way, a parasitic oscillation can cause a transformer to vibrate like crazy. I wonder if it's possible there's an oscillation happening that you can't hear? This is why I asked about the voltage earlier btw, an oscillation would lay into the power supply causing it to sag.
     
  19. Linkjr

    Linkjr Tele-Meister

    Age:
    50
    Posts:
    116
    Joined:
    Aug 16, 2017
    Location:
    Uk
    Thanks Sds1, Unfortunately after powering off and on the buzz is back, I also took my switch out of the equation and setup as stock no bypass cap, low output and mechanical buzz.
     
  20. Linkjr

    Linkjr Tele-Meister

    Age:
    50
    Posts:
    116
    Joined:
    Aug 16, 2017
    Location:
    Uk
    So need to take some measurements

    my b+ was around the 340 - 350 range last time I needed to measure it and was definitely not buzzing at the time.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.