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Turntable hums thru amp even without t'table power?

Discussion in 'Receivers and amplifiers' started by b104, Apr 3, 2006.

  1. b104

    b104 Member

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    I own an old Pioneer SA-410 amp that works perfectly with anything I usually connect to it.When I try to connect a "newer"? plastic covered Pioneer turntable PL-Z93 it immediately starts to hum,even without power being supplied to the turntable.It runs off a 12v power supply,so has a jack rather than a mains plug (turntable).I've cut the jack off & spliced a 12v 500ma trannsformer onto it but the hum is constant even without power to the turntable.I'm sure it has something to do with the earth as when I touch the pickup arm the hum drops considerably as does earthing the amp which has never been needed before.(phew).Really appreciate an answer to this pain in the butt!
     
  2. boxwrench

    boxwrench Guest

    b104,Run a wire from the metal chassis on the turntable(look underneath the cabinet) and connect it to the ground screw on your amp,that should take care of the problem.The hum you are hearing is caused by the tone arm and cartridge not being grounded.

    Best of luck.
     
    Last edited by a moderator: Apr 3, 2006
  3. gerry1

    gerry1 Guest

    Boxwrench is absolutely right. Even new amps usually have a grounding screw on the rear though.

    OOPS!...misread your reply box, my apologies!
     
    Last edited by a moderator: Apr 3, 2006
  4. boxwrench

    boxwrench Guest

    @gerry1, Not a problem,you know one thing concerns me though,500ma. sure does'nt seem like enough to sufficiently power that t/t motor.I would think something a bit higher would be better and certainly would not do any harm. Just my other 2 cents worth!
     
    Last edited by a moderator: Apr 3, 2006
  5. b104

    b104 Member

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    Thanks for replies.Straight after posting,I ended up running an earth wire internally out to the amp & it worked perfect.The case is one of those all plastic bodies & the only external screw is'nt an earth anyway.Regarding the 12v transformer I wired onto it,it might get a bit hot.The only other transformers I can wire to it are, an old Nokia Salcompoy 12v 800 ma or an AC 12v.6A 7.2va adaptor. Would one of these handle the load better?
     
  6. b104

    b104 Member

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    Thanks for replies.Straight after posting,I ended up running an earth wire internally out to the amp & it worked perfect.The case is one of those all plastic bodies & the only external screw is'nt an earth anyway.Regarding the 12v transformer I wired onto it,it might get a bit hot.The only other transformers I can wire to it are, an old Nokia Salcompoy 12v 800 ma or an AC 12v.6A 7.2va adaptor. Would one of these handle the load better?
     
  7. boxwrench

    boxwrench Guest

    Great,I'm glad that worked out for you. Now for your power supply...what if any voltage and amperage requirements are marked on the t/t case or chassis?
     
  8. b104

    b104 Member

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    Nothing anywhere inside or out,just 12 v dc input.I was thinking that maybe an old Nokia phone charger rated at 800ma would be a safe enough step up without doing any damage?
     
  9. boxwrench

    boxwrench Guest

    That will probably be better,it certainly won't hurt.All you can do is use it and see.The worst that could happen is burning the little transformer up.
    Have fun with your system!
     
  10. b104

    b104 Member

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    No worries,thanks.It,s only the turntable I was worried about damaging.That's why I posted the original thread rather than just trying to earth it. Cheers!
     
  11. boxwrench

    boxwrench Guest

    Yep,as long as you don't exceed the voltage requirements the current will not cause a problem. A motor will only draw it's max.current at full load (or start up in some cases). As long as the demand does not exceed the supply you'll be in good shape.If demand does exceed the supply the transformer will fail, and this is why having extra current available will not hurt.Now if you know what the max. current draw of the motor is you could provide a fuse to protect both the source and the motor, but thats another lesson for another day!
     
  12. gerry1

    gerry1 Guest

    Thanks to both of you...this has been informative. You know your stuff box! You lost me after the grounding wire question LOL!
     
  13. boxwrench

    boxwrench Guest

    Aw shuks Gerry!It's just another day at the office.lol!

    I have to know this stuff,it's how I make my living.
     
    Last edited by a moderator: Apr 5, 2006
  14. gerry1

    gerry1 Guest

    What do you do?...are you an elecrtician or something of the sort?
     
  15. boxwrench

    boxwrench Guest

    Well,yes and no...I'm a machinist/electrician...etc...
    I install and repair machinery for a corrugated box company,so I get to do it all.
    High voltage,got to love it!
     
    Last edited by a moderator: Apr 7, 2006
  16. b104

    b104 Member

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    Believe it or not,I emailed Pioneer stating the model no. & asked what the amperage would be(PL-Z93),Back when I first started this post.They replied that they knew of a PL-Z92,94,95,96 etc but had no record of my model no.93.They suggested that the amperage of the models similar but not the same as mine was about 300 ma.(Unbelievabable) If this is the case,do you think that I should scale back to the 500 ma adaptor or not worry?
    I replaced it with an 800ma adaptor & seems to work ,no worries!
    P.s. I have'nt ran it for prolonged periods though,so am not sure.
     
    Last edited: Apr 10, 2006
  17. boxwrench

    boxwrench Guest

    Don't worry,It will only draw what it needs.Now spin some vinyl man!
     
  18. redspecialist

    redspecialist Newbie

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    Hi - I'm having the same problem with a Pl-z93... what did you connect the wire to inside the turntable, and how did you get it in there??
     
  19. ps355528

    ps355528 Regular member

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    the problem is grounding for the signal wires.. or an earthing "loop" .. don't know the specific turntable, and getting a reply from people who last discussed this in 2006 (hint.. it's 9 years ago) will be unlikely..

    I guess the turntable connects to the amp with a pair of RCA connectors?.. correct? .. does the amplifier have a "true" ground connection or is it just a twin wire for the power from the wall? (not interested in how the turntable is powered).. If there is no "true" ground you can get hum.. the simplest way if you have a true ground on the supply is to run a wire from the metal of the amplifier chassis (jam it under a screw somewhere) to that true ground.. and see if the him remains.. usually this will cure the problem as the signal leads will link that true ground to the screens of the signal cables, but not always, in which case you really need to seek some advice from some of the dedicated vintage hifi forums.. because grounding/loops can get hellishly complicated to sort out. Once you get a ground sorted (not "mains ground" which is often just the "neutral" wire grounded somewhere between the power station and your house and can be full of all kinds of weird noise!!) but a proper EARTH connection.. European supplies have to have them by law!.. US and other places not so sure.. then your whole setup should only have ONE.. not every bit of equipment or you get eddy current loops and hum again... weirdly adding any bit of equipment with a proper ground will sort hum problems for the entire system..

    It's quite an art grounding sound systems for no buzz/hum.. (believe.. I was a live sound engineer back in the day and hum was a nightmare on a rig with upwards of 60 feeds going all over the place under buzzy lighting setups.. often took longer to trace and kill a "rogue" buzz than sound checking 6 bands!!)
     
  20. redspecialist

    redspecialist Newbie

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    thanks for your reply!
     

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