I think my HDX is broken again (2 weeks after NAIM service)

Does the HDX have the fixed/floating earth switch on the back? Maybe you just need to change the option - have a look in the manual as to which you should use.

Thanks for the quick reply. I have tried both positions and this has not solved the issue unfortunately (just tried again right now to double check)

Never mind. I'd mail Naim and ask for advice. Do you have dedicated mains feed - with that system you really should. It isolates the system, and sounds better too.

I will email them and see what they suggest, it will be intriguing to see if this occurs with a bog standard CD player with a digital coax out, I'll do that first before borrowing any equipment from work. I could have a dedicated spur added to the consumer unit as my setup is about 5m away from it. The lights are on a different ring main to the ring powering the audio equipment so my instinct suggests that a dedicated spur will not fix the problem. I might get an Electrician in to inspect the quality of the Earth.

 " the repair I would expect everything to be tested before it leaves their factory, the issue could of course be with the QBD76"

Is the title of the post entirely fair then?

G

Change the coax cable out before you do anything else.  Could be as simple as the shielding on the coax is broken and what appears to be transient RFI is entering your system and triggering the protection on the QBD76.  The fact that no interference is happening over the optical cable is simple, The optical passes only light whereas the coax passes an electrical signal, therefore virtually impossible for RFI to occur over an optical cable.

Also, if you can try your QBD76 into another device in the same environment do so.  It is entirely possible that the protection/filtering system in the QBD76 PSU is responsible for the music cutting out when it senses the additional RFI from the other appliances.  It could be set to too fine a tolerance and hence responsible (again the coax could be responsible as the entry for the RFI; do a coax change test first).  Trying the device with another system in the same environment will be very instructive from a troubleshooting perspective.

Hi Geofiz,

I will certainly try swapping out various kit first. I do appreciate the fact the fibre optic cable isolates the ground between two systems. That is why I tested both the coax and and fibre optic. I thought it was interesting that the issue dissapeared when selecting the fibre optic, my logic suggesed that the issue could be down to something external to the QBD76.

Hi GraemeH, your right, my title is a little unfair. When writing this I was pretty frustrated, I've just upgraded to a 252 and Supercap, at this level of investment in audio equipment you just expect this gear to work with no messing around, I'm also looking at the QBD76 as the cause as well. 

Hmmm,

For the hell of it I just tried a cheap little Micromega MyDac on my HDX using both optical and coax connections and tried to duplicate your problem without success.  Cycled lights on and off, made the refrigerator cycle, no issues. 

Definitely interesting issue and maybe Naim themselves can shed some light on the issue.  Have been contemplating trying some high end Dacs to use with the HDX. Be interesting to know if anyone has had a similar issue using the Naim DAC.

Hi lovethatsound,

Thats very interesting, this suggests that there could be a design flaw in the HDX power supply (either a grounding issue or power rail regulation) to the circuitry supporting the digital coax out, but I'm not going to draw any firm conclusions before having a chance to change equipment around and talk to Naim and Chord Support. Just out of interest what did you do to solve your problem?

This is to the Naim techies, I'm measuring 810K ohms (Suggests that the HDX is using an isolated supply for the digital out to avoid ground loops?) between the digital out BNC screen and the mains ground, the QBD76 measures 0.3 ohms. Is this to be expected? I get the same result on the HDX with the ground switch in either position.

Matt

Hello Wackymatt and lovethatsound,

My HDX is the 1TB HD unit and I am using an XPS to power it at the present time (maybe that is why the RFI it is not an issue in my setup?; I have had other HDX issues that Naim was able to correct however).  Not sure how this impacts how things are powered internally to the HDX.  When you encountered the issue were you using a separate power supply or the HDX on it's own? 

Mine was upgraded to the 2TB version from the 1TB as part of the repair, I wasn't provided a record of what internals were changed during the repair when the HDX was returned to me. I have re-iterate the that the digital out on mine was never used until I got the HDX back from Naim as I bought my DAC just a few weeks ago. I do have an XPS, having it connected or not it makes no difference to audio issues

Well I've tried a new digital coax cable and another DAC plugged in to the HDX, I have also changed mains leads, disconnected network cables etc.. so that the bare minimum of cabling connects the HDX and DAC. None of this has fixed the problem.

All I need to do now is get another source and plug it in to the DAC. If the problem goes away then it really does look like my HDX is faulty. 

Can you use your computer as a source to your DAC to do the test?

I could do, I think it only has optical out though, but I'll check the motherboard manual to see if a header exists somewhere. I have tried it with USB connected to the QBD76 and I had no problems whatsoever, my local Naim/Chord distributor should be happy to lend me something though.

Hi lovethatsound,

I have a strong feeling you're right. I want to check first by using another source into the DAC. I'll then phone Naim support for advice. 

If Naim aren't helpful I'll investigate the issue in much more detail myself. I'm an electronic engineer working in acoustics (not hifi related at all though) so I have the skills & equipment necessary to troubleshoot this issue and diagnose the fault (component and/or design) and maybe even come up with a fix. I hope I don't have to do this though as I'm pretty busy at the moment.

Has anyone else had interference issues with their HDX or is it just the two or us?

With HDX:NDAC & DC1 coax I never had any problems.

G

Well I've tried another source and problem goes away. The HDX is at fault. Plugging a network cable in the back even causes the music out the digital Coax to cut out, I'm not very happy!

Oh yes, I know this problem too. But now it get's even worse. I have frequent dropouts in the music, no difference if it's coming from the NAS or internet radio. On other days there are only dropouts when I turn on the lights anywhere in the house. My HDX was already once in service, they didn't find anything. I had an electrician in the house, he measured everything and found nothing. 

Today I played back music from my MacBook Air over FireWire (into my Weiss DAC 202). Yes, of course, not a single problem, it sounds at least as good or even better than the HDX.

On my Weiss DAC on the display the sampling rate is displayed. Whenever I get the dropouts with the HDX instead of the sampling rate of the song it displays "unlocked", so I think it has really something to do with the signal from the HDX. My interconnect is BNC.

So if Naim has a solution for this problem I'm eager to know too. I was already thinking of selling my Naim gear :-(((