random interruptions in playback with Digi + pro

[wormcycle]

It was the first time it happened, it sounded like not sufficient buffer size, I increased the auto buffer size to 4096, no effect.
I had need using this setup for few weeks no issues. The connection is coax to Modi Multibit.
I tried the same DAC same amp from PC (with the same NAS connection) with Jriver - works fine. Any ideas what could be going on?

[Kilgore]

Hi Wormcycle. I have a similar issue. About once an hour the sound drops out for one second or less. Did you ever resolve this?
My storage is a 1 TB USB drive plugged directly into the Pi.

[Stephane]

Hi,

Same here, increasing the buffer size does nothing, I still have interruptions from time to time mostly on music from my NAS and not on radio streams.
I suspect it is related to the network access, I am using the inboard Wifi interface with an external antenna (https://raspberrypi.stackexchange.com/q ... -to-a-pi-3).

[Kilgore]

I also increased buffer size with no effect. but I have made some progress with my particular issue.

I noticed that the drop outs happened when a light switch (plugged into the power circuit not the house light circuit) was switched near my gear. I then found that I could trigger the drop out by switching some other items on and off in the house. Strangely it was more often when switching off a light than switching on. Now that I could trigger the behavior I was able to do a bunch of troubleshooting to isolate the fault.

I could hear the relays in the Schiit Bifrost DAC clicking when the fault was triggered.
I have two power circuits in the house and swapping power to the other circuit had no effect. Whether it was the Pi or the DAC or both.
I reduced the Pi power requirements by removing the USB HDD and playing music from a USB stick - no effect
I plugged in headphones directly into the Pi - no drop outs
I connected DAC by USB & Optical - no drop outs
I substituted a battery pack for the mains power, but sadly the small one I have did not have the guts to power the system.

Therefore the issue appears to only be in the RCA coaxial connection from the Digi Pro+ to the DAC, and independent of the Pi3.
I eventually dragged out my old 35Mhz scope and had a look at the signal on the coaxial cable. Sure enough, there is a big glitch when I triggered the drop-out. This was still the case even when the DAC was disconnected. it was also visible even if music was not playing. Therefore the relays clicking was simply the DAC responding to the glitch.

Still not clear what the root cause is. My next step I guess is to try a more powerful power supply and/or power the Digi Pro+ interdependently. I have just ordered a 3A supply....who knows, perhaps it has better supply noise rejection.
If that does not help, then I will try to power the system via a battery supply to see the effect.

I should mention that I am currently using a 2.5A switching plugpac supply.

(of course I could just use the optical out, but I want to stick with the coax and also I am using the DAC optical input to connect directly to my CD player)

[uwedamm]

Hello
Did you enable the "high-power" configuration in /boot/config.txt
# setting the max usb current to 1200mA
max_usb_current=1

Did you connect the USB harddisk directly to the RPI? I got a similar problem in the past and it disappeared after
connecting the harddisk via powered USB hub
A friend of mine solved the same issue by setting up a linear regulated power-supply with high current capability.

I think the RPI is sensitive to voltage drops of the power-supply (and the usual switching power-supplies are not stable (even if rated to 2A or above)

you could check the dmesg output, does it show failures of the harddisk?

Uwe

[Kilgore]

Thanks for the info Uwe. I will try checking / changing the settings as you suggest. I also received a new 3 amp power supply today and will try that when I get home.

However I'm starting to think that this is a shielding issue for the transformer and coax. HiFi Berry make it very clear that the DAC should be earthed.

My DAC has the case tied to house earth but the shields on the RCA's (in and out are tied together) are not tied to the case. The RCA's are ultimately earthed by my power amp, but as the shields pass from the coax to the RCA lead to the preamp (NAD 703) through RCA leads to the power amp and from the power amp to house earth, they pick up about 3 ohms when measured from the DAC to house earth.

Anyway, I will try your suggestions and the upgraded power supply first. If this doesn't work, then I will try to improve the DAC common to earth connection, first by cleaning plugs & sockets and possibly higher gauge RCA leads.

[Ancipital]

I believe the Bimby is earthed via the IEC lead, no? That being the case, open the jumper on the Digi+ Pro to correctly engage the galvanic isolation.

"With the jumper there is a high-resistance ground connection to make sure the receiving side isn't on a floating potential" - as Hifiberry put it. So with the Mimby, which uses a wall-wart with a two wire cable, it needs the jumper closed. My Gumby is (apparently) earthed like your Bimby, so I run it with the jumper open.

It should be as simple as opening the jumper, hopefully.

[Kilgore]

HI Ancipital.....thanks for the heads up re the jumper. I had no idea that the Pro+ had this. Now that you educated me I ran a search including the term 'jumper' and came up with a number of interesting items including this one

Yesterday I tried a different power supply but as I expected, it made no difference. Not surprised, as using USB memory stick instead of HDD made no difference, but hey, it was worth a try. And the config setting was already at 1200 mA.

I will try to find time over the weekend to try various shielding and grounding changes in the signal chain and in particular I'll see if I can reduce the resistance to real Earth in the chain of shields between my components.

[Ancipital]

I think you're over-thinking it. Get a clean 2A or above PSU for the Pi. Try opening the jumper. It shouldn't require any more special treatment than that.

It may well be that you're not giving the Pi enough juice, anyway- Pi 3 does need a bit more. Getting the jumper right just helps a bit with noise, usually.

(My Gumby is rock solid with it open or closed, incidentally. I'm powering the Pi from a 5v iFi iPower, which is 2.5A, and despite their silly marketing, very clean for a switcher, indeed cleaner than some ebay special LPS units.)

[Kilgore]

I doubt that it is the supply. I had upgraded to a better quality 3amp supply a few days ago. Issue persists when HDD is removed to reduce power draw. A few minutes ago I removed the Digi+ Pro jumper but it made little or no difference. Did all the weekend chores today so tomorrow I will have time try a few other avenues.

(Fallback is of course to use the optical ...but I'd really prefer to get the coax going if possible)