random interruptions in playback with Digi + pro

[Kilgore]

OK...I have come to the conclusion that the Digi+ Pro is just very sensitive to radiated EMF and I’m unfortunate enough to have some devices and/or house wiring that radiates enough to glitch the spdif signal.

I spent a whole day fooling around with every possible combination of earthing....both with and without the Digi jumper in place.

I tested the robustness of the house earth and it was good.
I ran a separate earth line from the house earth into my listening area so I could try different arrangements.
This included tying the coax shield to earth via a 1000 ohm resistor, via a 100 ohm resistor and direct to earth.
Also tried tying the power supply 0V to earth.
I also tried running the Pi and Pro using a battery power pack....so it was completely isolated from any house wiring or power supply.
I even ran it within a steel toolbox, and earthed the box.

The lights that are giving me grief are a pair of halogens...fed with a transformer. So these will present a collapsing field when turned off. I put an identical one on a long lead, fed from the power circuit from the other side of the house. I found that I could switch it without issue at a distance, but as I closed to half a meter or so, I could trigger the fault....and this is with my Pi running from a battery pack and using a usb stick for a source ie no power, NAS or LAN connection. This is demonstrating that the glitch is radiated through space, and appears not to be transmitted by the power supply or other connections.

I will now try suppressing the issues at the source. [halogen lights, stove ignitor, washing machine cycling – these are all within 6 meters of the Digi+] I have already tried a couple of small ferrite suppressors on the lights.....but they were pretty small and had no effect. Perhaps a judiciously placed X and Y class cap may do the trick.
I am also putting together a linear power supply.....mainly because of ACX and others recommendations for SQ. But hey, perhaps I’ll be surprised.

And for the record, I measured the resistance connecting Digi coax shield to Digi 0V with the jumper in place as 10kohm. So when in place it is only loosely tying the output common to ground....just enough to stop it floating. Removing the jumper completely isolates the spdif output.

One good thing to come from all this was that I discovered that the 7” touch screen I am using was much more responsive when I tied the Pi 0V to house earth. It was a bit flaky before so I have tied the Pi to earth and all is good.

[Ancipital]

Oh man, what a voyage of discovery.

Maybe this is the excuse you need to build it all into a nice metal box?

[Kilgore]

Just a quick update. I purchased a small mu-metal can, about 25mm x 20mm x 20mm high. I trimmed down the height to about 10 mm and insulated the edges with electrical tape. Putting the can over the transformer on the Digi Pro output plus the can lid underneath the board had no effect.....the glitch remained. Of course the can is not totally enclosing the transformer, but hey, it was worth a try!

[Kilgore]

Probably my last update on this issue.

Over the last week I built a linear power supply. Mostly to provide a clean 5V to my Pi (have you ever looked at the output of a switching supply on a scope? Yuk!) As the supply is earthed I was able to remove the jumper from the Digi board. I didn't really expect this to fix the power switch glitch issue.....and it didn't.

I also wired a commercial EMF filter into the power line of one of the lamps that creates the glitch. But again this had no effect.

So I remain using the optical instead of the coax. Not such a big deal but it would have been nice to have solved the problem. Who knows, perhaps one day I will try out a DigiOne https://www.allo.com/sparky/digione.html instead.

[pacapona]

Hi,
Did you have found a solution?
I have the exact same issue!
With optical output i can't play all my songs... 24/192

If i can't find a solution i will have to switch to another solution for playing my music...

[Kilgore]

I'm afraid so. I suspect that aside from perhaps replacing my halogens with LEDs and somehow making some other major changes to the other sources of the interference (the gas stove igniter for example) the only other way to get the Digi+ Pro coax out to be glitch free would be to put the entire board and assembly within a mu-metal box....but then I would need x-ray glasses to view the touch screen.

Fortunately for me most of my material is FLAC rips of CDs so optical is OK although coax would be preffered.

I saw this interesting post a few days ago from Mike Moffat [grand master of DAC design and responsible for all digital stuff coming out of Schitt Audio]

They have just released a USB to SPDIF converter. It also boasts isolation for the SPDIF output and they are also reporting drop outs for a small number of users. Mike states that 'that we can do nothing about this other than defeating the complete isolation'....'and offer refunds'
So it seems that perhaps by having robust isolation it increases the sensitivity of similar circuits to picking up radiated spikes.

I have my hopes pinned on the next Rune release having support for an allo.com DigiOne
This was mentioned in post 64 of the RuneAudio 0.4-beta for Raspberry Pi2/3 thread

Ah...hope springs eternal!