1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

5E3 120 cycle hum

Discussion in 'Amp Tech Center' started by tripley, Feb 4, 2021.

  1. tripley

    tripley TDPRI Member

    Age:
    22
    Posts:
    11
    Joined:
    Feb 4, 2021
    Location:
    New Brunswick, Canada
    Hey everyone,

    I recently finished building this 5E3 style amp. The thing sounds awesome but it has a nasty 120 cycle hum going on. I've already gone over the lead dress and the grounding of the amp and I am now at a loss.

    The hum only increases with the volume on the bright channel and the normal volume doesn't seem to affect it at all. When I ground the grid of V1A the hum is tamed and the bright volume no longer has an effect. Any thoughts? See the pictures to get an idea of the wiring (don't worry about the missing input haha, I'm still waiting on some parts so I grounded the normal inputs for now)

    Thanks in advance!! PXL_20210205_012619545.jpg PXL_20210205_012637857.jpg
     
  2. gabasa

    gabasa Tele-Meister

    Age:
    49
    Posts:
    342
    Joined:
    Jan 29, 2018
    Location:
    Toronto, ON
    Where's the fourth input jack? Can that have anything to do with it?
     
  3. tripley

    tripley TDPRI Member

    Age:
    22
    Posts:
    11
    Joined:
    Feb 4, 2021
    Location:
    New Brunswick, Canada
    Yeah don't worry about that, I'm still waiting on some parts so I grounded the leads that go to the input for now (I only have the bright inputs wired up at the moment). That should be fine
     
  4. Jon Snell

    Jon Snell Tele-Holic

    Posts:
    798
    Joined:
    Aug 31, 2015
    Location:
    Jurassic Coast. UK.
    Screenshot 2021-02-05 at 10.34.18.png Why are you not grounding the pot to the preamp ground and using the chassis ... that will cause hum if the chassis point chosen is not a 'star' point.
    Screenshot 2021-02-05 at 10.22.57.png
     
    Last edited: Feb 5, 2021
    loopfinding, Wally and Nickfl like this.
  5. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,452
    Joined:
    Dec 30, 2019
    Location:
    california
    Can you show the ground scheme?

    Is there a schematic and layout for this hybrid?
     
  6. tripley

    tripley TDPRI Member

    Age:
    22
    Posts:
    11
    Joined:
    Feb 4, 2021
    Location:
    New Brunswick, Canada
    PXL_20210201_004758308.jpg PXL_20210205_220454960.jpg PXL_20210205_220501633.MP.jpg
    Here's the whole layout of the amp, I've got the first and second filter cap grounded at the transformer stud with the center tap of the heaters and 380V. The preamp is grounded at the input jack as shown and tied to the rest of the preamp components through a ground plane on the back of the board. I'll post the schematic when I get back to my computer. It's pretty much a 5e3 with an extra gain stage and a reverb circuit.

    Thanks again!
     
    Lowerleftcoast likes this.
  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,452
    Joined:
    Dec 30, 2019
    Location:
    california
    Is the speaker output from the OT grounded to the chassis?
     
  8. tripley

    tripley TDPRI Member

    Age:
    22
    Posts:
    11
    Joined:
    Feb 4, 2021
    Location:
    New Brunswick, Canada
    Yeah it's a mercury magnetic FTDO-59 with the negative lead tied to the transformer housing that grounded to the chassis with the mounting bolt. The outside of the chassis is powder coated so it doesn't conduct but the bolt is fastened inside where it's bare aluminum so there is an electrical connection there.
     
  9. D'tar

    D'tar Friend of Leo's

    Posts:
    3,375
    Joined:
    Jan 11, 2013
    Location:
    WNY
    5e3?
    Do you have a schematic?

    Is the ground trace separated between the pre and power amp?
     
  10. 2L man

    2L man Tele-Meister

    Age:
    61
    Posts:
    379
    Joined:
    Nov 23, 2020
    Location:
    Finland
    I have noticed when "ground" and "chassis" are used in a same sentence it cause noise problems :(
     
    D'tar likes this.
  11. tripley

    tripley TDPRI Member

    Age:
    22
    Posts:
    11
    Joined:
    Feb 4, 2021
    Location:
    New Brunswick, Canada
    Here is the schematic. On the board I have a separate ground plane for the pre amp and power amp.
     

    Attached Files:

  12. tripley

    tripley TDPRI Member

    Age:
    22
    Posts:
    11
    Joined:
    Feb 4, 2021
    Location:
    New Brunswick, Canada
    Just a correction on my initial post: its the NORMAL channel that causes the hum to increase with volume.
     
  13. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,452
    Joined:
    Dec 30, 2019
    Location:
    california
    Like Jon said, get the ground off of the pot backs.

    Run a wire from the bright vol pot ground terminal to the normal vol pot ground terminal to the input jack ground terminal where the board ground is connected.

    Run a wire from the reverb pot ground terminal to the ground side of R25. The PI 56k tail resistor.
     
    Last edited: Feb 6, 2021
    Nickfl likes this.
  14. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,452
    Joined:
    Dec 30, 2019
    Location:
    california
    duplicate post
     
    Last edited: Feb 6, 2021
  15. schmee

    schmee Doctor of Teleocity

    Posts:
    14,927
    Joined:
    Jun 2, 2003
    Location:
    northwest
    Nice build! I can't tell ...but the preamp section needs grounded near the input jacks and not grounded near the power end. Is it?
     
  16. tripley

    tripley TDPRI Member

    Age:
    22
    Posts:
    11
    Joined:
    Feb 4, 2021
    Location:
    New Brunswick, Canada
    Thanks! Yeah the preamp is grounded at the input
     
  17. tripley

    tripley TDPRI Member

    Age:
    22
    Posts:
    11
    Joined:
    Feb 4, 2021
    Location:
    New Brunswick, Canada
    I've already tried not grounding them on the back of the pot and running a bus to connect them all to the input. No change
     
  18. archetype

    archetype Fiend of Leo's

    Posts:
    5,901
    Joined:
    Jun 4, 2005
    Location:
    Williamsville NY
    I keep seeing references to 120 Hertz (cycle) hum. Line voltage is 60 Hertz. Am I missing something, or is this an error that keeps being repeated?
     
  19. tripley

    tripley TDPRI Member

    Age:
    22
    Posts:
    11
    Joined:
    Feb 4, 2021
    Location:
    New Brunswick, Canada
    After rectification voltages will likely have some 120Hz ripple to them so that's where it comes from.
     
  20. D'tar

    D'tar Friend of Leo's

    Posts:
    3,375
    Joined:
    Jan 11, 2013
    Location:
    WNY
    Is this a kit? Do you have a layout of the board and the conductive traces?
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.