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Thread: hum help!

  1. #21
    Join Date: Oct 2016

    Location: Bolton, England

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    Quote Originally Posted by sq225917 View Post
    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.
    There's the same voltage between the positive and negative terminals on a cartridge whether it is wired balanced or unbalanced - there's no difference between the two.
    Also, a step-up transformer can be wired as balanced input with unbalanced output, or balanced at input and balanced output, or unbalanced input with balanced output, or unbalanced at both input and output. There's a multitude of options. The most common is unbalanced input and unbalanced output. In all cases the voltages are the same.
    Quote Originally Posted by hifi_dave View Post
    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.
    Yes, Rega's wiring shouldn't be a problem. I'm still trying to work out exactly what is wrong in the OP's setup but I'm confident it is that Rega's wiring uses just one signal negative as the ground for the arm but the SUT is linking both signal negatives together. Or maybe it isn't It's a lot easier having the equipment in front of you than diagnosing problems via forum posts.

  2. #22
    Join Date: Apr 2016

    Location: Issaquah, WA, USA

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    Guys, thanks for the feedback. I did another series of experiments:

    1. I removed the cart and shorted the red-to-green and blue-to-white wires using alligator clip wires
    2. To see if the tonearm continuity was missing, I checked between the tonearm and the SUT grounding lug, and it was there
    3. I opened up my SUT and checked continuity on all the grounds, it exists, which means all grounds are connected, but I couldn't find a way to isolate the input ground from the output ground as it seems they're connected somehow in the transformer. there are only two wires coming from the input connection (ground and signal) see this picture: https://www.pinterest.com/pin/483292603746340417/

    Could this be a component compatibility issue. I can't imagine ortofon selling something that is inherently poorly designed. Does anyone else have experience with this particular SUT?

    Thanks all!

  3. #23
    Join Date: Oct 2016

    Location: Bolton, England

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    Quote Originally Posted by sliderule3_14 View Post
    Pinterest requires a sign-up to see the picture, and authorisation to access all kinds of personal data. I didn't do that.

  4. #24
    Join Date: Oct 2016

    Location: Bolton, England

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    Here's a simple test which will be useful:
    disconnect the SUT from the preamp, but leave the interconnects which you had between SUT and preamp connected to the preamp's inputs. Insert a pair of shorting sockets into the free ends of the interconnect (where the SUT was). Is there any hum?
    Now touch the earths of the two shorting sockets together. That will create an earth loop. Does it hum now? If so, it's because having the L/R earths connected at the far end of the interconnect has created an earth loop which the preamp has problems with. Some preamps don't hum when such a loop is created, some preamps do. The difference is due to the way the preamp's circuit is laid out on the circuit board.
    If you get hum when you do the test you will also get hum when the SUT is in place because the SUT is also linking the L/R earths together. To cure it you need to break that link (like I said in a previous post).

  5. #25
    Join Date: Oct 2016

    Location: Bolton, England

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    Quote Originally Posted by sliderule3_14 View Post
    ... I couldn't find a way to isolate the input ground from the output ground as it seems they're connected somehow in the transformer.
    Do not disconnect the input earths from the output earths. The L input earth should be connected to the L output earth. Same for the R channel. It's the L and R earths which should be isolated from each other. Read post #15 again.

  6. #26
    Join Date: Oct 2016

    Location: Bolton, England

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    Quote Originally Posted by hifi_dave View Post
    ...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...
    I hope the Headspace acquitted itself with honour

  7. #27
    Join Date: Apr 2009

    Location: Near Saffron Walden, Essex

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    It sure did. I have used it frequently for demos. It's one of those go-to items which I can take off the shelf and use without worrying about the performance or even if it will work.

  8. #28
    Join Date: Oct 2016

    Location: Bolton, England

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    Quote Originally Posted by hifi_dave View Post
    It sure did. I have used it frequently for demos. It's one of those go-to items which I can take off the shelf and use without worrying about the performance or even if it will work.
    Glad to hear it

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