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Thread: hum help!

  1. #1
    Join Date: Apr 2016

    Location: Issaquah, WA, USA

    Posts: 12
    I'm Andrew.

    Default hum help!

    Help!

    This is my setup:

    rega p3-24
    ortofon quintet black mc
    ortofon st-7 SUT
    audioquest big sur cables
    rogue audio rp-5 with 40db gain, 47kOhm input impedence phono input
    cardas cables
    NAD C275BEE amp
    KEF LS-50

    in a previous setup, I had the rega plugged directly into the rogue with the gain set to 60db and 30ohm load and it was dead silent when the needle hadn't dropped.

    my motivation is to use a separate phono preamp than the one built into the rp-5, so I've added a SUT--eventually, I will bypass the internal phono preamp and use a regular line-in on the rp-5.

    I've checked continuity on all the RCA outer sheath conductors to ground and there seems to be less than .5 ohm resistance. I checked that all my ground are connected--I have a grounding bar that connects all grounds together, with each ground connected to the bus bar with it's own wire.

    but with the addition of the sut, which is also connected to the same ground, there is a hum, even at low volumes (gets worse at higher volumes). when I touch the tonearm, the tone of the hum gets deeper but the amplitude goes up (gets louder).

    additionally, with the SUT added and the hum, I can hear the volume knob clicks as I turn up the volume!

    Any suggestions?

    Thanks!


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  2. #2
    Join Date: Jun 2011

    Location: Skien, Norway

    Posts: 905
    I'm Jostein.

    Default

    It might be a ground loop between the SUT and the turntable. Can you try to connect the ground cable from the SUT to the Rouge audio preamp instead?
    My hifi system:

    Turntable: Technics SL-1200 MKII, Ortofon 2M Bronze cartridge, Mike New bearing, MCRU PSU (c), Oyaide HS-CF headshell, Oyaide MJ-12 TT mat, Vantage Audio Copper mat, Isonoe Isolation Feet, Isodek IF-2 isolation platform, Furutech Monza LP stabilizer, Herbie's Hal-O JR damper Phono Stage: Hagerman Cornet 3 (prototype) Amplifiers: EAR 868L Preamp, Transcription Audio 211 Heaven Power amp, Bob Carver Cherry 180 power amp CD Player: Ear Yoshino Acute Tuner: Magnum Dynalab 90T Speakers: Vandersteen 2CE SigII, Townshend Audio Super Tweeters, Transcription Audio Speakers Cables and stuff: LFD Audio interconnects and speaker cables, Mark Grant G2000HD, BlackCat Electronics, Van Den Hul Clearwater, Black Rhodium mains cables, Black Rhodium mains block, Finite Elements Resonator, Townhsend Stella Speaker stands, Pro Audio Bono hifi rack, Herbie's spike gliders, Herbie's Ultravox and Hal-O tube dampers, Super Black Hole CD mat Record Cleaning Machine: Loricraft PRC4

  3. #3
    Join Date: Apr 2016

    Location: Issaquah, WA, USA

    Posts: 12
    I'm Andrew.

    Default

    Quote Originally Posted by jostber View Post
    It might be a ground loop between the SUT and the turntable. Can you try to connect the ground cable from the SUT to the Rouge audio preamp instead?
    Jostber, i can give that a try when I get home. it seems like it would be equivalent to my current set up, though. the ground on the sut goes to a bus bar and the ground on the rogue goes to the same busbar. but Iíll try it anyways and see what i can see, or hear, that is.


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  4. #4
    Join Date: Apr 2016

    Location: Issaquah, WA, USA

    Posts: 12
    I'm Andrew.

    Default

    Quote Originally Posted by jostber View Post
    It might be a ground loop between the SUT and the turntable. Can you try to connect the ground cable from the SUT to the Rouge audio preamp instead?
    jostber, no dice. the hum is still there. iím probing with my multimeter. perhaps iíll find something.


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  5. #5
    Join Date: Dec 2017

    Location: Ontario, Canada

    Posts: 22
    I'm Dan.

    Default

    Does your tonearm have the extra ground wire or is it wired like a typical Rega with ground connected to the RCA shell?

  6. #6
    Join Date: Apr 2016

    Location: Issaquah, WA, USA

    Posts: 12
    I'm Andrew.

    Default

    Quote Originally Posted by Blackdog View Post
    Does your tonearm have the extra ground wire or is it wired like a typical Rega with ground connected to the RCA shell?
    itís the typical rega ďintegratedĒ rca ground


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  7. #7
    Join Date: Dec 2017

    Location: Ontario, Canada

    Posts: 22
    I'm Dan.

    Default

    it’s the typical rega “integrated” rca ground
    And that may be where the problem lies. It isn't a ground loop, it is a lack of ground, or more precisely lack of shielding ground.
    A couple of clues. Touching the arm changes the tone and amplitude, and it is volume dependent. I don't know exactly how the Ortofon is wired , but I suspect the ground to the RCA input jack is isolated from the output and from earth ground. With that ground missing, the tonearm is picking up all kinds of noise.
    Try this - With all the ground wires in place (I assume one from the transformer to the Rogue), take another piece of wire and attach it to the ground post and touch the ground on the RCA jacks (probably input jacks). Does the hum change or even disappear?

  8. #8
    Join Date: Aug 2008

    Location: Suffolk, UK

    Posts: 948
    I'm Paul.

    Default

    I find that a couple of lengths of wire with crocodile clips at each end are useful when trying to find a grounding problem. You can makes various ground connections between outer rings of rca plugs, binding posts, tonearms etc. Worth checking voltages differences with a meter first before making a connection as if there is a fault you might have quite a a voltage difference and you might get a bit of a loud pop.
    ~Paul~

  9. #9
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 865
    I'm Andrew.

    Default

    Yes, I suspect the Rega's odd scheme for for earthing the tonearm is the root of the problem. The usual way (which is most problem-free) is for the L/R cartridge -ve pins to each have their own wires (connected to the RCA plugs -ve side) and no connection between them. Then a separate earth wire comes from the tonearm and the rest of the turntable's metalwork to the earth terminal on the phonostage or preamp. The earth wire should not connect to the cartridge's L/R earths except at the earth terminal on the phonostage or preamp. It should be possible to get hum-free performance with the system wired that way.
    However, re-wiring the tonearm would be a fiddly and/or costly job, and it must be possible to get hum-free performance with Rega-style wiring, as you have proved with your original setup (with cartridge straight into the preamp).

    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.

  10. #10
    Join Date: Apr 2009

    Location: Near Saffron Walden, Essex

    Posts: 5,513
    I'm Dave.

    Default

    Selling Rega turntables and arms for over 40 years, I can state that I have never experienced 'hum' caused by Rega's earthing arrangement. The screens and metalwork is earthed via the right channel plug and screen. For confirmation of the effectiveness in this case, the OP states that it was "dead silent" before the SUT was added.

    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'.

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