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Bah, humbug! Troubleshooting help needed . . .

Discussion in 'Amp Tech Center' started by dean, Nov 21, 2020.

  1. dean

    dean Friend of Leo's

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    OK - so I bought and assembled one of those little, cheapo 14-watt amp kits on eBay. I figured for $25 I might learn a little before maybe tackling something more substantial. After figuring out the values of all the resistors and caps, it soldered up pretty nicely and looks appropriate. And overall, it really sounds pretty good with my Tele. Of course, there are issues that may make it unworkable. I just need some ideas where to start troubleshooting. Here’s what I got:
    1. The small blue LED does not light up. I assume it should.
    2. There is a fairly significant hum when it has power running through it. I know that with some setups grounding occurs when you touch the strings on the guitar, but that has very little impact on the hum. What does have an impact it touching the Bass and Treble pots which significantly increases the hum.
    I’d like to get rid of the hum, but I really don’t know where to start. I believe all the wiring and connections are done correctly (+ to +, and cap orientation). The speaker sounds fine when other amps are run into it. Any suggestions where I might begin looking? Thanks!

    [​IMG]
     
  2. fender4life

    fender4life Friend of Leo's

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    From the hum you say happens when u touch the pots, I would take a second look at all the resistors and make sure theres not a much smaller value somewhere. It;s often easy to miss the color on the 3rd band and end up with a 100 ohm where a 100k should be etc.
     
  3. Jon Snell

    Jon Snell Tele-Holic

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    The LED issue maybe just wrong polarity. Take the LED out and turn it around.
    The hum from the pots is probably an earthing issue, when mounted on a metal front panel and ground is connected to them, that should improve.
     
    hepular and Wally like this.
  4. dean

    dean Friend of Leo's

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    Thanks for the help - I appreciate it.
    I double-checked all the resistor values, and they are in the correct slots. One resistor was turned around, but that shouldn’t make a difference. I’ll turn the LED around to see if that helps. The only other issue I can think of is with the caps on the Bass and Treble circuits - there was some confusion between a cap that was labeled 2A471J and one labeled 2A472J - their values were 470pF and 4,700pF respectively. Could having those in the wrong slots make a difference?
     
  5. hepular

    hepular Tele-Holic

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    yep.

    dude on guitar wiring bunch on facebook silenced his guitar by getting those values switched, since he boosted his tone control's highpass filter to 13k hz, thus ensuring that only dogs could hear him play.
     
  6. 24 track

    24 track Doctor of Teleocity Silver Supporter

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    looks like a fun kit , where did you get it?
     
  7. dean

    dean Friend of Leo's

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  8. schmee

    schmee Doctor of Teleocity Silver Supporter

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    Does it go into a chassis? maybe it's humming because it needs everything grounded like the pots all on a metal faceplate? and faraday surrounded too?
     
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