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    Audio input conductors?

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    Maintarget

    Posts : 209
    Join date : 2013-02-10

    Audio input conductors?

    Post by Maintarget on Fri Jul 26, 2013 9:43 pm

    I'm a new member in the process of building a VTA ST-120 and will be relocating the audio input to the rear of a custom enclosure I have access to some Belden #9418 4 conductor AWG 18 with 19X30 stranding with a full outer shielded of aluminum foil polyester tape.
    Would this be suitable for this application?
    If so should i use two conductors per input or one?
    or should I use twisted pair of kit supplied wire and use careful routing?
    Thanks for your opinions.

    sKiZo

    Posts : 1312
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Audio input conductors?

    Post by sKiZo on Fri Jul 26, 2013 10:01 pm

    I went with both ...



    http://www.performanceaudio.com/item/Mogami-W2549/5604/

    22 gauge twisted pair in a full woven shield. I plan to run one length for both channels and ground the shield at one end as a drain. Plan is to run it as far from everything else as possible. Trade off there is the longer the run, the more chance it'll pick up RF or other interference, but it's pretty robust stuff. Probably best not to tie it down TOO tight until you're satisfied that it's as clean as it's gonna get.

    I also plan to make a metal box or add a plate to shield the inside connections behind the jacks as those are close to the transformers. That should help, and I don't expect it would hurt.

    *If you do use a foil jacketed cable, there should be a "drain" wire that gets hooked to ground. This is usually a solid bare conductor that's run behind the foil - lots easier than trying to terminate the foil itself. Once again, just terminate one end and clip the other end flush so you don't get a ground loop.

    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: Audio input conductors?

    Post by tubes4hifi on Sat Jul 27, 2013 10:51 pm

    nice link sKiZo !!
    I've been using some S-VHS video cable for years for doing wiring in amps and preamps, but on your link what I see that is most similar to what I use is
    the W2947, it's smaller diameter so easier to use and has an individual ground shield around each signal conductor, it's perfect for phono input wiring
    and would also work great to run ST70 inputs from the rear side, and very inexpensive for such good cable!
    W2947

    sKiZo

    Posts : 1312
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Audio input conductors?

    Post by sKiZo on Sun Jul 28, 2013 12:12 am

    Happy to be of service ...

    I'm a fan of Mogami ... their pure series cables are outstanding, but even their basic wire is way ahead of stuff selling for much more. I've got somewhere around 28 of their 3503 and 3506 RCA pairs in my system and no noise. Connectors are real solid, and the jacket is super flexible ...

    Just in case you thought I was kidding about the cables ... purists, please close your eyes ...



    Somebody stops me!!

    ramon68

    Posts : 87
    Join date : 2009-04-12
    Age : 76
    Location : naples fl

    Re: Audio input conductors?

    Post by ramon68 on Sun Jul 28, 2013 7:34 am

    That is just wrong...wrong on so many levels...

    tubes4hifi
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    Re: Audio input conductors?

    Post by tubes4hifi on Sun Jul 28, 2013 10:55 am

    kind of like . . . a variety of music! Very Happy 

    arledgsc

    Posts : 340
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Audio input conductors?

    Post by arledgsc on Sun Jul 28, 2013 11:24 am

    I like Roy's solution the best (Mogami W2947).   In this case each signal is individually shielded and low capacitance with respect to the shield (18pF/ft).   I've used the Mogami W2549 in low impedance, balanced applications.  It's great wire but might the wrong application here.   In stereo audio the Mogami W2549 is going to tightly couple the left and right signals together for the cable run.   The W2549 has 3.4pF/ft capacitance (very low) between the two conductors plus each conductor has additional 23pF/ft capacitance with respect to the shield.  It may work OK though as it is excellent cable but remember the input impedance is high on the ST-120 and small capacitances affect the upper frequency response.  The Belden 9418 takes this to another level with 39pf/ft capacitance between conductors and 79pF/ft capacitance with respect to the shield and other conductors.  So there is a lot more capacitance associated with the Belden cable.  Nothing wrong though in wiring it up to see how it sounds.  But you may want consider a different cable type.   The Mogami W2947 is about $0.50 a foot so very affordable plus eliminates the cross coupling of signals inside the cable.

    Mogami W2947 S-video
    Mogami W2549 Balance
    Belden 9418


    Last edited by arledgsc on Sun Jul 28, 2013 11:42 am; edited 1 time in total

    peterh

    Posts : 680
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Audio input conductors?

    Post by peterh on Sun Jul 28, 2013 11:34 am

    Maintarget wrote:I'm a new member in the process of building a VTA ST-120 and will be relocating the audio input to the rear of a custom enclosure I have access to some Belden #9418 4 conductor AWG 18 with 19X30 stranding with a full outer shielded of aluminum foil polyester tape.
    Would this be suitable for this application?
    If so should i use two conductors per input or one?
    or should I use twisted pair of kit supplied wire and use careful routing?
    Thanks for your opinions.
    Talk to your plumber :-) mount an iron tube, make shure it's connected to the "ground star" and pull your
    cables through it. Iron will shield magnetic field is addition to electric ones ( cables usually only
    shields electric fields).
    A 6mm ( or 1/4 inch for those inclinded )tube will suffice, a 90 degrees angle might benefit the mount.

    Maintarget

    Posts : 209
    Join date : 2013-02-10

    Re: Audio input conductors?

    Post by Maintarget on Sun Jul 28, 2013 4:44 pm

    Gentlemen (You too sKiZo:D)
    sKiZo the back of your system looks like a bowel of spaghetti that spilled!
    Thanks for the advise on shielded cable great stuff so my next question is were can I purchase some Mogami W2947 by the foot?

    sKiZo

    Posts : 1312
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Audio input conductors?

    Post by sKiZo on Sun Jul 28, 2013 5:18 pm

    ramon68 wrote:That is just wrong...wrong on so many levels...

    Yeah ... I know ... but to each their own. Me and "simple" don't get along all that well. Looks a lot prettier on paper ...



    I also tried keeping the wires organized better for a while, but I'm constantly moving stuff in and out of the system. Also ... didn't notice any difference in playback quality. You'd think with all the interconnects I'd get SOME noise or degradation, but that hasn't been the case. If I feed it a good source, the blacks are truly black, and the music's right 'n tight. Who could ask for more?

    Back to the wire ... I think yall got me convinced to pick up on some of the W2947 cable. The W2549 I got is more for microphone applications anyway, which would help explain the impedance specs. Truth be told, I didn't spot the other stuff when I was shopping. Looks like I could also split the cable and run one input up either side of the chassis for even more isolation - or more potential for RF interference. Six o'one, etc ...

    Here's a link to the Mogami 2947 by the foot ...

    http://www.performanceaudio.com/item/Mogami-W2947/6395/

    sKiZo

    Posts : 1312
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Audio input conductors?

    Post by sKiZo on Sun Aug 04, 2013 5:24 pm

    tubes4hifi wrote:nice link sKiZo !!
    I've been using some S-VHS video cable for years for doing wiring in amps and preamps, but on your link what I see that is most similar to what I use is
    the W2947, it's smaller diameter so easier to use and has an individual ground shield around each signal conductor, it's perfect for phono input wiring
    and would also work great to run ST70 inputs from the rear side, and very inexpensive for such good cable!
    W2947

    OK then ... I just ordered some of the W2947 cable ... along with some interconnects and adapters I needed anyway so I qualified for the free shipping. Something to keep in mind if you're ordering the small stuff ... just a few feet of the W2957 would have been $14 S&H ... yeowch!!

    So ... a pause in the action while the wire wends it's merry way to my mailbox. A question comes to mind ... what to do with the shield? I figured to terminate one end to ground to act as a drain and let the other float on each wire?

    PS ... the Mogami interconnects they sell are real nice too. I got a LOT of interconnects and it was a real joy to find a quality inexpensive cable to upgrade all the odds and ends that were in the system. All Mogami now ... and one happy camper here. Try em ... you'll like em!

    http://www.performanceaudio.com/item/Mogami-3603/10731/

    (also available in 1 and 6 foot lengths.)

    sKiZo

    Posts : 1312
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Audio input conductors?

    Post by sKiZo on Wed Aug 07, 2013 2:44 pm

    Got the Mogami W2947 wire in today and thought I'd post up a head to head comparison with the W2549 ...



    Thanx Roy ... I think this is gonna work a lot better!

    Lot's more flex, so it'll be easier to tuck in nicely. One thing that stiffens out the W2549 significantly is the extra solid plastic rounds in the bundle. Hadn't planned on those. Strain relief? The W2947 comes flat, but I also took the liberty of splitting the cable and  doing a twist, then securing the end with 1/4" heatshrink. Could make a difference? Who knows, but it's easy enough to do. Even with the twist, it does corners that the W2549 objects to. I also plan to run one section up each side of the case for each input using just the center conductors for signal, then tie both shields together and use those as a drain. That should provide max isolation ...

    arledgsc

    Posts : 340
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Audio input conductors?

    Post by arledgsc on Sun Aug 11, 2013 11:46 am

    " I also plan to run one section up each side of the case for each input using just the center conductors for signal, then tie both shields together and use those as a drain. That should provide max isolation ..."
    With the W2947 I think I would connect the individual shields to each RCA jack separately and at the board input tie the shields together by connecting to board GND.  This way the shields don't carry the opposite channel return current on the board-to-RCA jack cable runs.  Effectively you are just extending the interconnect cables.

    Maybe perhaps I don't quite understand what you are trying to do.  Are you suggesting using two W2947 cables for each channel - one for the signal and the other employing the center conductor for the ground return?   If so I don't think it will buy you any better performance.   You won't get any common mode rejection on these single ended inputs as you would with true balanced inputs.

    Nice avatar!  Scott

    sKiZo

    Posts : 1312
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Audio input conductors?

    Post by sKiZo on Sun Aug 11, 2013 12:45 pm

    Thanx for the kudos on the avatar ... had a slow day AND photoshop ... deadly combo. tongue 

    Yeah ... I was thinking of just using the center conductors, one for +, one for -, and length of the W2947 per side. Twist the cable grounds together and attach those directly to the chassis. My thoughts are that those would act as an extra layer of rejection for any rf that might otherwise hit the signal wires. Similar to a foil wrap on a cable - those have a drain wire that works the same way. Also run each length of cable down opposite sides of the chassis to minimize cross talk.

    Maybe overkill, but I keep hearing groans about the length of the inputs due to moving the jacks to the back. I do plan to tuck them up close to the sides, but that puts them right on top of the chokes ... not sure if that's an issue or not.

    No rush ... beautiful, dry weather, and I just so happen to have a roof that needs fixing ... joy!

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