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Thread: hum help!

  1. #11
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    Quote Originally Posted by hifi_dave View Post
    I would suggest you look at the earthing arrangement and siting of the SUT. If the SUT is anywhere near anything with mains on, it might well pick up 'hum'.
    That's a good point which I forgot to mention. Nearby mains transformers can induce hum into the SUT, though moving the SUT only a few inches (any maybe turning it through a few degrees) can reduce the hum dramatically.

    Over the years I've had lots of people contact me regarding step-up transformers which hum, and they nearly always start by saying they have "an earth loop" causing hum. Sometimes that's the case but often it isn't. The other two most common causes of hum are:
    1) placing the SUT too close to a mains transformer, and
    2) using unshielded interconnects between the SUT and phonostage.

  2. #12
    Join Date: Apr 2016

    Location: Issaquah, WA, USA

    Posts: 12
    I'm Andrew.

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    Quote Originally Posted by RothwellAudio View Post

    This is what you need to check first: with nothing connected to the Ortofon transformer, check if there's continuity between the earth post on the transformer and the earth sides of the RCA sockets. It would be best if there isn't, but check that and then get back to me with your findings.
    Hi, there seems to be continuity between the grounding post and all the RCA earths. Is that bad?

  3. #13
    Join Date: Apr 2016

    Location: Issaquah, WA, USA

    Posts: 12
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    I also performed the following checks:

    with a banana plug on the SUT ground (using the free end to touch) and the SUT ground wired to the preamp ground:

    I touched the green wire and the buzz on the right channel increased dramatically
    I touched the blue wire and the buzz on the left channel increased dramatically
    I touched the right channel of the rega rca earth and the right channel buzz increased dramatically
    I touched the left channel of the rega rca earth and the left channel buzz increased dramatically
    I touched the SUT right output rca earch and no increase in buzz (which is weird since I thought I had continuity with all the ground post on all the SUT rca earths)
    I touched the SUT left output rca earch and no increase in buzz (see above aside)
    I touched the tonearm bare metal and the buzz in both channels increased notably

    I also moved the SUT away from my setup with no change in buzz

    additionally, I swapped the SUT output interconnects (which are audioquest big sur cables) with Schiit Pyst cables with no change in hum.

    Not sure what I'm dealing with here as I'm not an electrical engineer

    Thanks all for your feedback!

  4. #14
    Join Date: Feb 2013

    Location: W Lothian

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    I'm Grant.

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    I had a hum appear on my setup the other day. Only thing I'd done lately was changed CD players to the oppo. It was the tonearm plug very slightly loose
    Regards,
    Grant ....

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  5. #15
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    Quote Originally Posted by sliderule3_14 View Post
    Hi, there seems to be continuity between the grounding post and all the RCA earths. Is that bad?
    Possibly, in this case it is bad. Those RCA sockets have nylon washers to isolate them from the metalwork, so it should be possible to break the connection between the RCA earths and the earth post.
    Try this if you're confident with a bit of rewiring:
    Keep the earth post connected to the metalwork, but break the links between the negative terminals of the RCA sockets and the earth post. The earths of the right channel input and right channel output should link to each other and to the right channel transformer. The earths of the left channel input and left channel output should link to each other and to the left channel transformer. There should be no connection between the left channel earth and right channel earth.
    Use a ground wire to link the earth post on the SUT to the earth post on the preamp. Try it with/without the ground wire to see which is quieter.

  6. #16
    Join Date: Apr 2016

    Location: Issaquah, WA, USA

    Posts: 12
    I'm Andrew.

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    I looked up some SUT schematics and several did have the grounds tied together. However, upon opening the case, I did see that only the output grounds where tied together explicitly. There where insulating washers for the input grounds, but somehow there was continuity with all the grounds, but I couldn't tell how. Am I missing something?

  7. #17
    Join Date: Oct 2016

    Location: Bolton, England

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    I don't know. Maybe I'm missing something. I told you how to wire the SUT. You can choose to wire it like I said or choose to wire it some other way.

  8. #18
    Join Date: May 2008

    Location: A Strangely Isolated Place in Suffolk with far away trains passing by...

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    I'm David.

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    Rega arms are earthed in a way to suit Rega! Most of the time when these arms are used on other decks it causes no issues at all, but I have known hum problems to arise occasionally and just sometimes, the phono stage used doesn't help either. I assume the hum is there all the time and with stylus lifted off the record?

    Induced hum is a different thing and can be due to magnetic fields from nearby transformers all adding up, so if a Rega or Grado mm cartridge is to be used, or especially a low output mc type, careful siting is essential if a Rega deck is used although in this case it may be just an earthing arrangement.

    In this particular case and bearing in mind the deck is a Rega complete, it may be a good idea to try or borrow a different mc stage, such as a Rega Fono MC, purely to keep it all in the family and to check the arm wiring hasn't gone awry if nothing else...
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  9. #19
    Join Date: Mar 2010

    Location: Sheffield

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    I'm Simon.

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    Rega use the signal gnd wire on one channel as the gnd. Which is fine in single ended phonostages which throwaway signal - on both channels by grounding them to the phonostage chassis.

    But step up transformers don't do that, they use the full voltage swing between signal minus and plus on each channel. They retain the fully balanced signal that comes from the cartridge. Rega assumption that they can do what the hell they like with one signal - from the cart is the root of the issue.

    You need to rewire your tonearm. No amount of fiddling will otherwise fix this. As long as signal- in one channel is used as earth it'll always hum.
    Kuzma Stabi/S 12", (LP12-bastard) DC motor and optical tacho psu, Benz LP, Paradise (phonostage). MB-Pro, Brooklyn dac and psu, Bruno Putzeys balanced pre, mod86p dual mono amps, Yamaha NS1000m

  10. #20
    Join Date: Apr 2009

    Location: Near Saffron Walden, Essex

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    I'm Dave.

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    Just done a dem using the Rega P6 with Ania cartridge. Now, of course, this uses Rega arm wiring, which I have never found to be a problem. We were trying various step up transformers and a Rothwell Headspace. There was no hum, buzz or any extraneous noises from the Rega set up - total silence and that's the way I have found it to be with numerous, various Rega turntables over the years. The Rega wiring is practical and not a problem.

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