Adcom GDA-700: Use splitter on RCA outs OR use XLR + RCA outs?

Discussion in 'DACs' started by northpaw, Dec 25, 2017.

  1. northpaw

    northpaw Active Member

    Messages:
    298
    Location:
    New England
    I have an GDA-700 DAC hooked up via RCA outs to my system, and very happy with it. I've now got two systems set up. For the second one, I've fed it from the analog outs of a CD player, but I would like to run this second system off the DAC as well. I don't want to run them at the same time, but I'd like to leave the hook ups in place.

    The GDA-700 has both balanced (XLR) and unbalanced (RCA) outs; the manual is silent about if they can both be hooked up at the same time.

    Seems I could use a Y-cable (or solid adapter) to split the RCA outs to send to the two systems. I expect some signal loss if I do that, but I believe there is more than enough output (voltage) from the GDA-700 to make this work. Alternatively, I could use an XLR(f)-to-RCA(f) adapter (Hosa makes some) for the second RCA connection. My understanding is that the Hosa XLR(f)-to-RCA(f) adapter grounds the pin needed to turn its RCA output to unbalanced.

    Is there any advantage of doing this one way or the other; that is, will having both the RCA and XLR outs hooked up simultaneously, or using a splitter on RCA outs, cause any issues? I'm not concerned about a lower signal level due to a split, but I would be concerned if either set up would cause a degradation of other aspects of the signal quality. I'm including a sketch of the schematic for the final outs.

    GDA-770_outs.png
     

     

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  2. olderroust

    olderroust AK Member

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    when I've done similar things I use a selector rather than a split cable or two runs of cables.

    A rotary selector connected to the source via its amp connection and to the amps via source A and source B works well for me

    When I've tried it with a Y cable its always degraded the sound, sometimes dramatically (the odds of a ground loop are fairly high.)
     
  3. whoaru99

    whoaru99 Epic Member

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    Using Ys on the RCA output normally isn't a problem. There should be no practical loss of signal unless the source impedance is unusually high, or the net parallel load impedance is unusually low.

    If I read the schematic correctly, it appears the RCA jack tip and XLR Pin 2 (hot) are in parallel anyway, basically same as using a Y off the RCA.
     
  4. northpaw

    northpaw Active Member

    Messages:
    298
    Location:
    New England
    Thanks for these replies, guys. I see much truth in both points of view. A switch is a proper solution, but I'd just as soon not build or buy one if I can get good results out of a split (probably a $13 investment), either of the RCA outs, or using both RCA and XLR outs (whoaru99, thanks for the confirmation that either way is essentially paralleling the outputs).

    So I take it that the key is getting the proper pairing of the output impedance from the GDA-700 and the input impedances of the preamp sections of my equipment (in this case, a Nak SR-3 and a Nak TA-2). This is also what the literature from Hosa indicates on using the XLR-to-RCA adapters: This cable is designed to connect gear with XLR outputs to gear with phono inputs. For best results, match the low output impedance to the high input impedance.

    The GDA-700 has an output impedance of 77 Ω (unbal) and 150 Ω (bal.). The Nak preamp sections each have an input impedance of 20,000 Ω.

    I also took a look at the schematics for the input sections on the Naks, and confirmed the inputs run directly to the selector switches. So I imagine that if I do not leave the selector in the CD position on the unused equipment, the outs on GDA-700 will not see the paralleled impedance (which if present would drop the effective input impedance to 10K Ω, right?), but will only see the little bit of additional capacitance/inductance from the cabling used in the split + the little bit of internal wiring in the Naks. I would be using double shielded interconnect cables, video or digital grade, which I know to have low capacitance.

    So I will give doing a split a try and see if I can get away with cheap and simple. Thanks again.
     
  5. whoaru99

    whoaru99 Epic Member

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    77 ohms unbalanced to net load of 10k should be no problem.

    General rule of thumb is 10:1 load to output impedance or better (higher first number). Your pairing would be about 130:1.
     
  6. northpaw

    northpaw Active Member

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    Thanks for that.
     
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  7. olderroust

    olderroust AK Member

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  8. whoaru99

    whoaru99 Epic Member

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    FWIW, I'm suggesting not bother with the XLR jack as there appears to be no point/benefit in doing that. Just Y off the RCA.
     
  9. olderroust

    olderroust AK Member

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    Location:
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    Ah, okay. My experience, and why I have the switchbox I have, is that going with an RCA splitter between three pieces of gear can result in audible excess noise and in some instances very audible ground loops.
     
  10. whoaru99

    whoaru99 Epic Member

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    I'd bet $1 that all the jacks in that switchbox are common ground.
     
  11. olderroust

    olderroust AK Member

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    My multimeter advises me not to accept your wager :)
     

     

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  12. northpaw

    northpaw Active Member

    Messages:
    298
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    Well, I happen to have an old pair of Y splitters -- with one male plug on one end and two female jacks on the other -- from at least 15 years ago, from when I connected both a tuner and a portable CD player to powered desktop speakers in my office (I swear, this was before iTunes, and if you wanted music, it was either a portable tape or CD player). These splitters are cheap ones from RatShack. But I hooked them up this afternoon as a trial, and they work without incident. No hum, and the sound, at least at first listen, seems unchanged. So I will get something similar but of better quality, and hopefully call it a day.

    I could see a 3-way split being more problematical than my situation (I just want to share my DAC with two amp/speaker sets, and I have everyone on the same power circuit). That switchbox is surprisingly affordable, and it is good to know of that option, so thanks for mentioning it and providing the link.
     

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