5e3 Hum

Discussion in 'Shock Brother's DIY Amps' started by Romartin, Jan 8, 2018.

  1. Romartin

    Romartin TDPRI Member

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    I know there are a lot of post on this topic, but it seems each one is a little different.
    Here is my issue:
    1. With the instrument cable plugged in either channel, there is a significant 60Hz hum that increases with volume.
    2. The hum changes when I thouch the chassis. It also changes if I wave my hand in the chassis (being sure not to touch anything).
    3. The hum is very minimal without the instrument cable in
    4. There is no hum in standby.
    5. There is no hum when V1 tube is removed.
    6. I have tried a different tube in V1 with no change.

    I really appreciate any insight into this issue!
     
  2. TNO

    TNO Friend of Leo's

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    It's really important that the preamp is grounded separately from the power amp. If you did a star grounding scheme try moving the preamp ground as far away as you conveniently can.
     
  3. hackworth1

    hackworth1 Friend of Leo's Vendor Member

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    Check your input jack wiring. 1M to from tip to ground. shorting switch tab to ground.

    Make sure the shorting springs are making full contact so that they short the tip to ground when no male jack is inserted.
     
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  4. Romartin

    Romartin TDPRI Member

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    So the bright channel, #2 input jack does not short the tip to ground when no male jack is inserted. You think this could be the culprit? what’s the best way to fix that?
     
  5. clintj

    clintj Friend of Leo's

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    Gently push out on the shorting contact a little bit at a time until you get:

    A. Good contact with no cable installed.

    and

    B. The contact fully opens when a cable is inserted.
     
  6. Romartin

    Romartin TDPRI Member

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    Thank you. I did this, and there was a slight improvement in hum when no instrument cable is plugged in, but no improvement with the cable plugged in. I will make a youtube video later to better show you all what is going on.
     
  7. D'tar

    D'tar Friend of Leo's

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    Are you meaning just a cable without guitar? That "will" be noisy. If, With nothing plugged in and chopsticking the jacks changes the noise level, then there is an issue with the jacks/shunts/grounds.
     
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  8. Wally

    Wally Telefied Ad Free Member

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    The basic noise level of the amp should be assessed with nothing plugged in. IF you have a cable plugged in with no instrument on the other end, then there will be a significant amount of noise generated because there is in effect an open input. If you have a guitar on the other end of that cable and you do not have a hand on any grounding point on the instrument, then there will be a grounding noise that will cease when you touch any grounding point...guitar bridge, strings, metal output jack plate, Tele metal control plate....or any metal on the amp that is connected to the amp’s grounded chassis.
    If you have this hum with a cable plugged in and you remove V1,then you have removed the 8nput Gain stage from the circuit and the kinds of hums created by an open input jack circuit, an ‘open’ ground contact at the guitar or the natural hum of a single coil pickup will naturally be elim8nated.
    Is this an amp you have built?
     
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  9. D'tar

    D'tar Friend of Leo's

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    bright input 2 shunt is connected to the tip of input 1. input 1 tip is shunted to ground with no plug installed. So without a cable inserted... yes it is shunted to ground.
     
  10. Romartin

    Romartin TDPRI Member

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    Yes it is one that I built recently. The amp is definitely very quit without a cable plugged in. The only time there is hum is when the cable is plugged in. There is less hum if I have a hand on the strings of the guitar. I made a you tube clip in which the cable is plugged into the guitar, but I wasn't holding the guitar or touching the strings.
     
  11. Romartin

    Romartin TDPRI Member

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    h
     
  12. Wally

    Wally Telefied Ad Free Member

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    When someone says that they have a cable plugged in, one wonders if there is anything on the other end of the cable. If one says that one plugs an instrument in, then we know that there is an amp, a cable and an instrument involved.
    If the amp is quiet with nothing plugged in, then one has to ask what guitar is being plugged in. The contact of the hand on the strings indicates that the grounding circuit is correct and that that aspect is of no concern. What type of noise remains is the question. That is, it would appear to me from afar that the noise you are hearing is normal....especially if it is single coil hum.
    What other amp do you use this guitar with? Is this noise replicated to some extent in that amp?
     
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  13. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Yep. I remember trying a new build with my P90 guitar. Thought I’d have to go on a massive hum-busting expedition. Actually turned out the amp is dead quiet.

    Nowadays for testing I plug in my noiseless strat via a short high-grade cable.
     
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  14. jjmantele

    jjmantele Tele-Holic

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    One must turn the guitar all the way down to asses amp-related hum accusations. Otherwise the pickups and other guitar stuff are in play. And a bad cable can still be the culprit and needs to be ruled out.
     
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