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AA1164 Princeton Reverb build BUZZ

Discussion in 'Shock Brother's DIY Amps' started by Paul Strat, Jan 11, 2019.

  1. Paul Strat

    Paul Strat Tele-Meister

    142
    Apr 7, 2017
    Muscle Shoals, AL
    F1393AB8-F5B4-4B06-A9F1-FB887A63752C.jpeg B79B2598-CA02-4013-B00E-DDEEBEC51492.jpeg 0048AD0C-55FC-4259-B724-E8E7A5317BE6.jpeg BA7FEF68-9354-4487-A9D8-0C968D9BACF5.jpeg 20E219F1-74F5-4E54-8606-C2C45FDE96B6.jpeg D6B7D748-B696-4C12-BC68-4F096A8A8AB4.jpeg 808552ED-C268-42E9-B664-BB744E26FF4A.jpeg 01FDC973-E804-4DEE-897C-C912DEB31BF8.jpeg New build with a buzz!
    Doing a (mostly) AA1164 Princeton Reverb build with Deluxe Reverb Transformers.
    The problem is a very annoying B note pitched buzz. The buzz is present with nothing plugged into the input, and increases significantly with an increase in the reverb level control. It also triples in volume amp f the reverb tank is disconnected. It has had this buzz since the first time is was fired up.
    It started as a straight Mojotone layout but I changed the output tube socket wiring to allow me to try 6L6 tubes, and added an additional 22uf filter cap.
    I’ll ask one question: since it has Deluxe Reverb transformers, should I add a choke?
    I will add with the exception of the reverb being a little stout, this is the best sounding “Princeton Reverb” I’ve ever heard.
    With that in mind I will open the floor to the amazing experts here at TDPRI....
     
  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    Knowing it's a B doesn't help us without the octave. You need to figure out it's 60Hz noise (likely grounding issue) or 120Hz noise (power supply).

    With any tube amp troubleshooting...

    -does it matter if a guitar is plugged in?
    -does turning any controls change the sound?
    -pulling any of the small tubes up to the power tubes cause it to go away?

    Those three things should help you isolate the area the issue is in.
     
  3. Paul Strat

    Paul Strat Tele-Meister

    142
    Apr 7, 2017
    Muscle Shoals, AL
    It’s there with nothing in the inputs
    Volume and Reverb controls increase and decrease it.
    Pulling V2 stops it completely
     
  4. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    Alright - that's progress :D the issue is pretty early in the amplification stages of the amp.

    When you pulled v2 was v1 still in? What if you put v2 back in and disconnect the reverb pan?
     
  5. Viejo

    Viejo Tele-Holic

    917
    Feb 12, 2011
    Central IL
    Do you have your shielded input cable grounded on both ends I can't tell. It should only be grounded on one end or it will cause a ground loop
     
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  6. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Do you have a tuner that shows Hz? "A-tuner lite" is what I use. Its pretty dead on with the scope.

    Chopstick around. Some of your wires run close and parrallel to your heater wires
     
    Paul Strat likes this.
  7. Paul Strat

    Paul Strat Tele-Meister

    142
    Apr 7, 2017
    Muscle Shoals, AL
    Yes, it’s only grounded at the inputs on the ground buss.
     
  8. Paul Strat

    Paul Strat Tele-Meister

    142
    Apr 7, 2017
    Muscle Shoals, AL
    The buzz gets a lot louder with the reverb pan disconnected.
     
  9. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec
    Paul, how are your filter caps grounded? I got a nasty buzz from a recent brown deluxe build when I tried grounding all four filter caps in the doghouse to the power supply ground. Doing it his way was implied on the original schematic and shown on the Mojotone 6G3 layout. Moving the ground for the preamp FC (the one furthest from the reservoir cap) to the preamp ground bus eliminated the problem.
     
  10. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    Just to be sure, you disconnected the cables at the amp side, correct?
     
  11. Paul Strat

    Paul Strat Tele-Meister

    142
    Apr 7, 2017
    Muscle Shoals, AL
    I’ve chopsticked and moved wires. I did shorten and move the lead to the reverb pedal jack away from the filament wire. That reduced the buzz some, but it’s still prominent.
     
  12. Paul Strat

    Paul Strat Tele-Meister

    142
    Apr 7, 2017
    Muscle Shoals, AL
    Yes, disconnected from the amp.
     
  13. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec
    Paul, one more thing. The heaters coming from your PT do not appear to have a centre tap, unless I'm simply not catching it in your photos. When there's no centre tap (usually a green/white wire) on the heaters, create an artificial centre tap by running a pair of 100R resistors from the heaters to ground. If you've done this, great. If not, it could be another source of your hum/ buzz.
     
  14. Paul Strat

    Paul Strat Tele-Meister

    142
    Apr 7, 2017
    Muscle Shoals, AL
    I have a can cap and an additional 22f cap in series as per the Weber layout for their 6A14HP. All grounded to the power amp ground. That’s a good thought.
     
  15. Paul Strat

    Paul Strat Tele-Meister

    142
    Apr 7, 2017
    Muscle Shoals, AL
    Right, no CT. I have the 100 ohm resistors from the pilot to ground.
     
  16. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    At this point it might be good to figure out what the frequency of this sound is. At least you know it's around/related to V2.
     
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  17. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec

    Definitely try moving the preamp cap ground away from the power to the preamp. You can just alligator clip it to try it out. I spent hours chasing the ground hum in my brownface... and that one simple move fixed the problem. The amp ended up quiet as a mouse.
     
    Paul Strat likes this.
  18. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec
    Okay, good move. Was just checking.
     
    Paul Strat likes this.
  19. Paul Strat

    Paul Strat Tele-Meister

    142
    Apr 7, 2017
    Muscle Shoals, AL
    Thanks to everyone so far. Will try to check the frequency of the buzz and move the preamp filter cap ground tomorrow.
     
    flyswatter likes this.
  20. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec
    If you don't have a signal generator, Google online tone generators and you'll find a bunch of WAV files/ little freeware generators that will provide you with 60Hz, 120Hz, etc files. Simply play these against the noise of the amp and you'll soon hear whether you've got the ground loop/ filter cap hum Corliss mentioned above.
     
    robrob and Paul Strat like this.
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