PL-71 hum

DocfosterDocfoster
edited August 2013 in Analogue
Turned on my PL-71 yesterday for the first time in ages.
It seems to have developed a loud hum (both channels), though the music still gets through. The hum stops if i disconnect the TT.
I've checked the ground and the ICs and all appears OK* with them. (The hum gets slightly worse when the ground is disconnected). I also took the base off the TT to check wiring to the rcas and earth and again, all looks well*.
Any ideas?
It's not an emergancy as i don't use it much, but would prefer it to be well.

* I want to stress that on such issues I am from Barcelona. All i can say is that no wires had obviously become disconnected.

Comments

  • uglymusicuglymusic
    Is there anything dead in the plinth?
  • DocfosterDocfoster
    I pulled out the corpse of a small rat.
  • uglymusicuglymusic
    Yeah. That would hum a bit.
  • DocfosterDocfoster
    Seriously, what were you suggesting?
  • DocfosterDocfoster
    edited August 2013
    Hmmm.

    The problem seems to be to do with some relationship between the other equipment in the setup and the phono front end.
    If i unplug the power amp while an LP is playing the hum disappears for the several seconds before the transformers in the power amp's psu discharge completely, the gain disappears and things go completely silent.
    If i unplug the phono stage the hum remains until the phono stage's psu have completely discharged (and things go completely silent).

    I'm hoping that may mean something to someone...

    (The hum is not present on other sources.)
  • AlanAlan
    Dunno mate? Maybe Col will see this, or may I suggest an email to Jim?
  • uglymusicuglymusic
    Seriously, what were you suggesting?
    That it was a hum smell from something dead and decomposing.
  • figlet108figlet108
    Ben, I've been plagued by humming for years since introducing NVA amps into the system downstairs. I've spent hours and hours and hours trying to figure it out and haven't really got to the bottom if it. Other amps in the same set up don't cause hum, but at the same time the NVA amps don't cause hum in the attic system with the Quads... 

    From what I've understood with my experiments, the hum is either originating from within the system (from the mains, or a ground loop, or from one of the other components etc) or from the environment in the form of some kind of RFI, or a combination of both.

    First question is, when did you last switch on the PL-71 without hum and what kit has changed since then? Has it worked since you got the TSS mk3? Have you changed your cables or the layout of your cables since it worked?
    Did you change the interconnects to make sure they didn't have a broken connection?

    In any event I would look to taking your PL-71 to another system that is known not to hum and try and see if the PL-71 itself is the issue.
    Could the phono stage be picking up RFI/EMI? Does changing its location help?



  • DocfosterDocfoster
    Seriously, what were you suggesting?
    That it was a hum smell from something dead and decomposing.
    Ah. So we were on the same wavelength...!
  • DocfosterDocfoster
    Dunno mate? Maybe Col will see this, or may I suggest an email to Jim?
    I'm hoping someone like that will tell me how to locate the "hum cut" button...
  • DocfosterDocfoster
    Ben, I've been plagued by humming for years since introducing NVA amps into the system downstairs. I've spent hours and hours and hours trying to figure it out and haven't really got to the bottom if it. Other amps in the same set up don't cause hum, but at the same time the NVA amps don't cause hum in the attic system with the Quads... 

    From what I've understood with my experiments, the hum is either originating from within the system (from the mains, or a ground loop, or from one of the other components etc) or from the environment in the form of some kind of RFI, or a combination of both.

    First question is, when did you last switch on the PL-71 without hum and what kit has changed since then? Has it worked since you got the TSS mk3? Have you changed your cables or the layout of your cables since it worked?
    Did you change the interconnects to make sure they didn't have a broken connection?

    In any event I would look to taking your PL-71 to another system that is known not to hum and try and see if the PL-71 itself is the issue.
    Could the phono stage be picking up RFI/EMI? Does changing its location help?



    Yeah. I feel some further systematic investigation will be required.

    Interestingly when i was fiddling about with the spaghetti of wires round the back of the rig, the hum occasionally got better or worse, so maybe there's a loose / broken connection somewhere. Unfortunately i couldn't replicate these changes under more controlled conditions.

    I'm hoping to get my old Claymore mended soon, and that'll give me a lot more scope for testing where problems are elsewhere.

    I've listened to the TT hardly at all over the past year, so it's more of an annoying problem than an urgent one. If the TFS catches the hum, I'll be more concerned!
  • figlet108figlet108
    edited August 2013
    Interestingly when i was fiddling about with the spaghetti of wires round the back of the rig, the hum occasionally got better or worse, so maybe there's a loose / broken connection somewhere. 
    Either that or the movement of the wires is bringing them into closer proximity with a source of interference, e.g. a power cable.
  • RobHoltRobHolt
    Ben, this is definitely a ground loop if disconnecting an amp from the mains (while it still plays on stored charge) cures the hum.

    It sounds like the system is being connected to ground via both the the mains cabling and the interconnects.
    Does the PL71 have a three core mains cable, and if so does pulling its mains plug and rotating the platter manually kill the hum?
  • DocfosterDocfoster
    Rob, exactly the kind of analogue expert i'm looking for. Thanks. Answering those questions is difficult at the mo, as i am on the beach in st ives.
    In any event, at this distance the hum is inaudible.
    I will try out your suggestions on my return.
  • RobHoltRobHolt
    That's no excuse ;)

    Have a great holiday!
  • uglymusicuglymusic
    Rob, exactly the kind of analogue expert i'm looking for. Thanks. Answering those questions is difficult at the mo, as i am on the beach in st ives.
    In any event, at this distance the hum is inaudible.
    I will try out your suggestions on my return.
    FWIW I love St Ives.
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