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DIY phono cables

Discussion in 'd.i.y.' started by rockingdoc, May 20, 2020.

  1. rockingdoc

    rockingdoc pfm Member

    I am just about to make up some rca phono leads, using shielded twin core cable.
    I plan to connect the outer braid to the signal return at one end of the cable at one end only.
    Is there any advantage in putting a resistor between the signal cable and the shield?
     
  2. Vinny

    Vinny pfm Member

  3. Mynamemynaim

    Mynamemynaim 35yrs a Naim owner

    What vinny said!!

    I use high quality German microphone cable and neutrix plugs
    Excellent results
     
    Vinny likes this.
  4. JensenHealey

    JensenHealey pfm Member

    That would be a strange thing to do. Why consider it?

    Such resistor would interact with the input of the following stage, with unpredictable results. At the least you will interfere with the input impedance and possibly created a frequency filter.

    So no.
     
  5. Vinny

    Vinny pfm Member

    I think that you misread the OP. By signal, I presume (hope) it is meant return, not positive.
     
  6. rockingdoc

    rockingdoc pfm Member

    Yes signal return.
    I only ask because on taking one of Naim’s fancy cables apart, I see they do it.
     
  7. mansr

    mansr Objectionist

    Why not use proper coax cable?
     
  8. Vinny

    Vinny pfm Member

    Using coax where you use the screen as return, achieves not much compared to plain twin. This is a grounded screen with twin conductors. Also cheaper than cheap if you use Klotz.
     
  9. rockingdoc

    rockingdoc pfm Member

    any views on what Naim’s resistor is for?
     
  10. Vinny

    Vinny pfm Member

    Certainly no reason obvious to me. What value resistor? The screen is just that, so why stick a resistor in series?

    I know @Arkless Electronics loves odd-ball cable practises and theories, actually even some very commonplace ones ( :) ), so probably worth his two-penneth.
     
  11. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Assuming the two internal cores are used as signal and ground and the screen as just a screen and grounded at one end only.. the only possible explanation that occurs to me is that the resistor is to add some impedance and thereby limit RF current from RFI getting back into the amps grounding system. Probably a waste of time but may have some slight effect if you have a mobile mast or taxi radio transmitter very close by.
     
    Mike P and Vinny like this.
  12. rockingdoc

    rockingdoc pfm Member

    Thanks. It was a fairly low value resistor, but I’m not keen to dismantle again to check.The Naim Superline phono stage is hugely susceptible to RFI, so perhaps it is for that.
     
  13. Chops54

    Chops54 pfm Member

    Was it a capacitor and not a resistor? A regular poster here who's name escapes me suggests that the other end of the screen should be grounded also but through a capacitor or the screen will just act as an antenna. I must admit that when making pseudo balanced cables I only ground the screen at one end.
     
  14. Michael J

    Michael J pfm Member

    Pointless. Either ground it or don't. Imo.
     
  15. ramona

    ramona Music lover

    If you ever stumbled upon Jon Risch's suggestion for line level interconnect, one option was to ground the shield in one end and put a small value ceramic in the other to aim RFI suppression.
    I've done it some ages ago both with and without cap but I can't remember noticing any difference. I'm still using it (twisted 89259/89248 with shield) for almost a decade with connected shield and no cap.
     
  16. Chops54

    Chops54 pfm Member

    Not heard of Jon Risch but I'll check him out later.
     
  17. YNWOAN

    YNWOAN 100% Analogue

    An interesting thread and the Jon Risch blog is also an interesting read. The seems to strongly recommend Belden 89259 - but I can’t find anywhere that sells it by the metre - does anybody know of anywhere?
     
  18. mansr

    mansr Objectionist

    Consider a regular coax cable running between to boxes, e.g. a DAC and a preamp. What happens to external interference hitting the shield? It gets dumped into the signal ground of the connected devices, of course. Depending on the ground wiring, that can be a problem. The conceit of the cable construction discussed here is to somehow avoid such problems. Does it, though? Interference picked up by the shield is still dumped into the signal ground, causing exactly the same problems as before. To provide any benefit, the shield has to be connected to (chassis) ground separately from the signal ground. Obviously, this is not possible when using RCA (or any two-terminal) connectors.
     
  19. Vinny

    Vinny pfm Member

  20. mansr

    mansr Objectionist

    RS and Mouser sell 100'/30m reels.
     

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