Dynaco hummer

Discussion in 'General Electronics Chat' started by DynaKarl, Jan 14, 2015.

  1. DynaKarl

    Thread Starter New Member

    Jan 14, 2015
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    0
    A "newbie" needs help that I hope is out there!
    I have a Dynaco S70 amp that hums when on alone and when connected with a PAS 2 preamp. The hum is independent of volume knob position. Tubes are fairly new.
    When turntable leads are added, the hum is stronger and gets stronger as volume is increased.

    Is there any clever circuitry device to filter out hum? -- and not lose 60/120 cycles in music coming from the turntable? And not too pricey?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    You appear to have two problems:

    One is the hum which is independent of the volume. That may be due to a faulty filter capacitor in the power supply. You can parallel the caps with an external cap of similar size to see if it changes the hum. If so, then you need to replace the caps.

    The other appears to be a ground loop problem with the turntable. That involves examination of the ground scheme for the turntable to see where the loop may be.
    If the turntable uses a three-prong cord, that could be a source of the loop. You could try a ground isolator plug to see if that helps.
    Another thing to try is to remove the ground connection from one end of one of the shielded cables to eliminate that as a possible loop.
    Also you might try a direct ground wire from the turntable chassis to the amp chassis.

    Good luck.
     
  3. BR-549

    Well-Known Member

    Sep 22, 2013
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    Also......turn the room lights out and see if hum goes down.
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,056
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    What? :confused:
    How would room lights affect the amplifier hum?
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,370
    I have seen and witnessed this effect first hand.
    The client's room lights were on a light dimmer. Turning off the lights made the hum vanish completely.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    Yup, dimmers make a ton of noise and fluorescents tend to spew hum as well.
     
  7. BR-549

    Well-Known Member

    Sep 22, 2013
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    Back when transistor radios first come out........it was a mystery.
     
  8. MikeA

    Member

    Jan 20, 2013
    125
    17
    I have some Chinese PWM power supplies for room LED lights that can overpower a local 10,000W FM radio station. :D
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    Since CFLs became popular - I've won a few free all band radios, AM reception is pretty much impossible with any lights on.
     
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