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Millett "Starving Student" hybrid amp

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  1. Lil' Knight
    I'm done, and time for troubleshooting [​IMG]

    LED on. Both tubes look good. However, when I plug my headphones in, there's a huge noise coming out. I guess something wrong with the ground. Any idea on this?

    [​IMG]

    [​IMG]
     
  2. Jrome
    Hey, Just got mine in the mail today! Thanks!

    Question: Are the tubes supposed to fit all the way into the sockets? If so, is there supposed to be some resistance? I mean, I didn't want to force them in before asking.
     
  3. Jrome
    double.....Sorry!
     
  4. tomb
    Quote:

    Originally Posted by Jrome /img/forum/go_quote.gif
    Hey, Just got mine in the mail today! Thanks!

    Question: Are the tubes supposed to fit all the way into the sockets? If so, is there supposed to be some resistance? I mean, I didn't want to force them in before asking.




    Believe it or not, I personally tested every single one of the tube sockets after I glued them. Yes, there will be some resistance. However, I can assure you that all of them allowed me to insert the tube pins all the way until the tube bottom was resting against the ceramic. However, unless you're experienced with this, it's best to wait until you get them anchored into the PCB before fooling with them much. You can break the ceramic in half or rip off a tube pin (did that to a couple), otherwise. [​IMG]
     
  5. Lil' Knight
    So I got music coming out from both sides but the terrible noise is there [​IMG] is there any step I should check? Also, the tubes are damn hot only after 20 minutes or so, is it normal?
     
  6. Juaquin
    Tubes should be warm enough that you aren't comfortable holding your finger there for more than a second or two (scientific, I know). Remember that tubes only work when they are hot, hence the tube has heaters (the orange glow in the middle). I'd say you're probably ok.

    The terrible noise is probably a ground loop. Make sure all your ground solder points are 100% flowed and not cold.
     
  7. Dunceiam
    I'm using a PCB board for ground, should I also make a solder connection to the chassis?
     
  8. the_equalizer
    Quote:

    Originally Posted by Dunceiam /img/forum/go_quote.gif
    I'm using a PCB board for ground, should I also make a solder connection to the chassis?



    A good, solid connection that grounds the enclosure is usually a good thing to have, as the case will shield the internal circuits from noise.

    This, of course, only applies if the enclosure is made of a material that is a good conductor of electricity (e.g. metal)

    cheers!
     
  9. Lil' Knight
    Quote:

    Originally Posted by Juaquin /img/forum/go_quote.gif
    Tubes should be warm enough that you aren't comfortable holding your finger there for more than a second or two (scientific, I know). Remember that tubes only work when they are hot, hence the tube has heaters (the orange glow in the middle). I'd say you're probably ok.

    The terrible noise is probably a ground loop. Make sure all your ground solder points are 100% flowed and not cold.




    So when I move the volume knob and headphone jack around, the noise disappears for a while but then the problem still the same. Sound still comes out from both sides. Does that mean the problem is in the solder points of the volume and headphone jack?
     
  10. Juaquin
    It's possible, but my guess is that the noise disappears because you're touching it. I'm not certain what the technical reason for this is, but I've had it happen many time (both with amps that had ground loops / hum, and unstable circuits in labs).
     
  11. Lil' Knight
    Anything I should do to solve the ground loop?
     
  12. tomb
    Quote:

    Originally Posted by Lil' Knight /img/forum/go_quote.gif
    So when I move the volume knob and headphone jack around, the noise disappears for a while but then the problem still the same. Sound still comes out from both sides. Does that mean the problem is in the solder points of the volume and headphone jack?



    I'm not so sure it's a ground loop as this phenomenon that you describe above. (Of course, Juaquin and I are both making educated guesses - his thought is as likely as mine.) I thought it was an optical illusion at first, but it appeared in your photo of the PCB that one could see the holes in the pads around the headphone jack - especially the one in front. The front pads on the headphone jack are the ground connections.

    If you are still having issues soldering to grounded pads, you may need another soldering iron. At the least, I'd try to re-flow those joints. You need to have enough wicking that the solder flows up the sides of the metal contacts on the headphone jack - but be careful! It's still just a plastic body!

    If you have intermittent contact or lack of contact around those ground pads on the headphone jack and/or pot, it can cause a lot of noise - same for the RCA jacks, too. Make certain you've got good grounding wires and contact all the way from the RCA jacks to the input terminal block. Again, if you're not getting wicking all the way from the ground plane on the bottom to the part on top, there may be a potential that you're not getting a good connection to ground - with any part.
     
  13. tomb
    Just a hint to some of you new folks building with tubes for the first time. Yes, there will be resistance plugging a tube into a socket - especially if the sockets have been glued back together. As stated earlier, I personally tested each socket to make sure a tube would plug into it. However, I may have a little better touch on how to do this after doing literally hundreds.[​IMG]

    The proper method to plug in a tube - especially if there's some resistance in the socket - is NOT to jam the tube straight in there. Instead, try a gentle spiral rocking motion while pushing down. In other words, it's almost like pushing one pin in at a time, while turning and pushing the tube at the same time. If this doesn't work or it sounds too difficult, then rock the tube gently back and forth while pushing down. This rotates the pressure around the tube pins, equalizing the stress somewhat - same as alternating the lug nuts on a car wheel.

    After a few times of plugging and unplugging the tubes, the sockets should loosen up some. Meanwhile, hopefully you haven't shattered a tube. [​IMG]
     
  14. Lil' Knight
    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    I'm not so sure it's a ground loop as this phenomenon that you describe above. (Of course, Juaquin and I are both making educated guesses - his thought is as likely as mine.) I thought it was an optical illusion at first, but it appeared in your photo of the PCB that one could see the holes in the pads around the headphone jack - especially the one in front. The front pads on the headphone jack are the ground connections.

    If you are still having issues soldering to grounded pads, you may need another soldering iron. At the least, I'd try to re-flow those joints. You need to have enough wicking that the solder flows up the sides of the metal contacts on the headphone jack - but be careful! It's still just a plastic body!

    If you have intermittent contact or lack of contact around those ground pads on the headphone jack and/or pot, it can cause a lot of noise - same for the RCA jacks, too. Make certain you've got good grounding wires and contact all the way from the RCA jacks to the input terminal block. Again, if you're not getting wicking all the way from the ground plane on the bottom to the part on top, there may be a potential that you're not getting a good connection to ground - with any part.




    The wiring is pretty good and all have good connections with the terminal blocks.

    [​IMG]

    I'll check the solder pads on the headphone jack tomorrow. Maybe I'll reflow them on both sides of the PCB.
     
  15. Juaquin
    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    I'm not so sure it's a ground loop as this phenomenon that you describe above. (Of course, Juaquin and I are both making educated guesses - his thought is as likely as mine.)



    My guess is probably not as educated as yours. I'm just grasping at straws here [​IMG]

    This is probably a topic for another thread, but does anyone know why certain unstable circuits become more stable when you touch them? My guess is something to do with capacitance but I have no idea. I've had this happen with the occasional opamp and/or transistor in lab settings.
     
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