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Coax DAC input not working when DVD has HDMI cable connected

Discussion in 'audio' started by Linds, May 8, 2017.

  1. Linds

    Linds pfm Member

    Strange one this... because it used to work until yesterday.

    Denon DVD1730 Coax out to Hegel HD12 DAC Coax. The audio via coax is all broken up and intermittent. Having pulled the DVD player out of the cabinet and reconnected it all (except the HDMI cable, hmmmm) it worked fine. Thought it was a faulty coax cable which worked ok straightened out :rolleyes: but it turns out that when the HDMI cable is connected it causes the coax signal to go super crackly / intermittent.

    I've tried a different coax cable, power lead, HDMI cable, etc. and fiddled with the limited DVD player settings (Audio HDMI or Analogue — makes zero difference even if it's not trying to output audio over HDMI). It's even when the HDMI cable touches the case or the edge of the socket on the player it knackers the coax signal. It works fine through Optical output/input, unsurprisingly. The DAC from PC (Optical or USB) is fine too.

    Final strange thing: When I replicate the connections to my old Firestone Spitfire DAC it all works ok, i.e. with the HDMI lead connected. Maybe the superior resolution HEGEL is being more fussy with the signal?

    So, DAC or DVD-player fault? What? Why? How? :(
  2. Andrew.B

    Andrew.B pfm Member

    "It's even when the HDMI cable touches the case or the edge of the socket on the player it knackers the coax signal"

    All I can think is grounding issue? I'm wildly guessing the Hegel doesn't have a transformer on the coax line, and it's messing up the signals...
  3. Linds

    Linds pfm Member

    Thanks for the quick response. I don't really know what grounding issues are other than something earthy?? The DVD player has no mains earth. Maybe that's not relevant though...

    So as it's a newly appeared issue is it likely to be the DVD player or DAC?
  4. JohnW

    JohnW pfm member

    I suspect the DAC - it seems like it could have an internal grounding issue with its Digital Input.
  5. Werner

    Werner pfm Member

    Something groundy indeed.

    Through the HDMI the DVD connects to the TV, and presumably a set top box and thence to the incoming CATV cable, which is grounded somewhere. The DVD connects this ground to the DAC, which itself is locally grounded at its mains connection. The system ground is now, literally, all over the place, and susceptible to all sorts of crap.

    The solution: go optical between DVD and DAC.

    But because it seemed to work days ago (did it really?), have the DAC checked.
  6. Cesare

    Cesare pfm Member

    My thought is exactly this, you've got a ground loop somehow and this is causing problems. It's actually possible that the coax lead was *broken* when it was working, with only the signal connected, but not the ground, and that with a *fixed* lead, you've introduced a ground loop :)

    I'd have thought going optical if you have the option is a good place to start, but if you need to use an electronic interface, there are spdif isolation transformers that should be just the ticket, although i've not used one myself, someone will probably be able to suggest one if this is the way you want to go.
  7. Linds

    Linds pfm Member


    Well the DAC is still in warranty so not a major issue, but a bit of a nuisance.

    Based on the groundy thoughts, I've revisited the setup. It works 100% fine when the TV is switched off, even with the HDMI cable still connected. So, DVD player coax to DAC. DAC RCA to amp, etc. DVD player HDMI to TV. And Virgin Box HDMI to TV.

    Once the TV is switched on it goes all bonkers crackly/faded. Switch on the Virgin box and it gets marginally worse again.

    Just hate to think my £300 (when new) telly and £40 (2nd hand) DVD player are functioning ok vs £900 DAC. OMG.

    I already have both the Hegel's Optical inputs taken up. Virgin Box, optical out only. Lenovo Q190 PC for streaming, optical out only. There is an option of analogue out from the DVD player but that would be admitting defeat / failing to address a possible fault.

    [Footnote 1: Werner, it's a good challenge, did it really ever work? I've checked with the memory of the family and having had this DAC a year, we've definitely watched DVDs with this exact setup, cables n all]

    [Footnote 2: Cesare, unless the VdH Digi cable has an intermittent ground problem that once made it work, I'm doubting(ish) that it's cable related. However, if it could work without a ground, then can I just use a centre pin only wired cable? (presuming the screen is the ground?)]

    Thanks for all the advice. We never had this bother with VHS.....!
  8. Cesare

    Cesare pfm Member

    Assuming you have phono connects on the ends, just try pulling the lead out a little till the outside (ground) doesn't connect, and see if it behaves. I'm certainly not suggesting running this way, it's more an exercise in trying to work out what could have changed to make it suddenly stop working.

    Anyhow, it sounds like you've got optical or coax out from the player, but you're using all of the optical ins to your DAC. Do any of the other things you have connected have a coax out? Could you swap these around and see if the problem stops with a different combo?

    Assuming not, then you need to either have some sort of transformer to isolate the coax between the two devices, or you need to have an optical->coax conversion step, which will mean you can utilise the coax in on the DAC from an optical outputting component.

    optical->coax converters are two a penny (well, they show up from £10 or so), and isolation transformers seem to be harder to find, but they do exist. I'd probably look at a converter as they are readily available, and will make your problem go away. You will then have the choice of which optical out to stick through the converter, as you may worry about an adverse effect from the extra step. I'd personally not worry, but everyone is different, so bear this in mind if you go this route.
  9. Linds

    Linds pfm Member

    Tried the non-ground RCA test. It wouldn't play at all without the ground connected. Not sure what that means? Before the DAC goes back to Norway or localish dealer I'll try to borrow a similar DVD player to see if it behaves.
    For sanity I'll look into coax-opt converters to provide a cheap short-term solution.

    Thanks for the assessment & advice.

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