Starving Student PCB's

  1. Andy Mac
    Got it all hooked up on the workbench, powered it up, no smoke or sparks so that was a bonus.
    I plugged in some cheap earhones, hooked up my Fiio X3 and voila!! Tube magic!!!
    The tubes glow a nice even healthy orange and the mosfets heat up very well.
    When nothing is playing or the music is quiet, there is a loud hum... very annoying!!
    It increases with volume control and is the same on both channels. It is also present with no source being plugged in...
    I have wired my tube holders on wires and not directly to the board, will this effect it?
    I notice if I touch the tubes or the volume pot the hum changes...

    Any ideas or pointers?

    It's going into a wooden case once this issue is sorted...
     
  2. muskyhuntr
    Hard to tell without pictures and other info, but sounds like a grounding problem. From your description, one possible cause is that the pot case is not grounded.
    Check that input wiring is away from AC. Twist input wiring.

    Me
     
  3. Andy Mac
    Thanks for the help. I'll report back once done.
    Another thing, due to the case design, I am not soldering the tube sockets directly to the pcb.
    Is this an issue?
    Is it preferable to bunch all 9 socket wires together, spread them out or twist certain ones together?
    I just want to eliminate any potential noise....

    I have also lined the entire inside with aluminium adhesive foil. I will ground this to the pcb as well... is this a good idea too???
     
    Last edited: Jun 18, 2017
  4. Andy Mac
    IMG_0955.JPG IMG_0956.JPG IMG_0957.JPG IMG_0958.JPG Done. Sounds awesome. I'm more than happy for a first build.
     
    Last edited: Jun 27, 2017
  5. chitnik
    I joined this forum so that I could order a couple PCBs. And they are already on the way! Thank you fred_fred2004!
     
  6. chitnik
    I started building my BOM based on a BOM another member posted in this thread. After building the list, I noticed the other member used 1/8 watt resistors. Of course, the schematic calls for 1/4 watt resistors. Should I update my BOM to use 1/4 watt resistors? Or will the 1/8 watt resistors be okay?
     
  7. chitnik
    Never mind. I figured it out. They are "military spec" which means they are equivalent to 1/4 watt consumer spec.
     
  8. Detectit
    Are these pcb 's still for sale? Ordered the parts. And it's convenient to have a board.

    Looked on the ebay shop. But could not find anywhere.
     

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