Raspberry Pi multi dac over ambitious? (SOLVED)

Put this in tinkering, cos thats what i am doing, though may not be the right section, anyway…

I have an RPI3 (B) running Roonbridge through a HifiBerry SPDIF digi HAT and DietPi to my DAC with no issues. However, i also have an AQ Dragonfly Black and i was experimenting with the possibility of running this on the same Pi. This is mainly in preparation for A/B testing of MQA when Roon switches on first unfold, and just cos im curious

It works, but i am getting background static and a repetitive machine noise interference which is clearly not a ground loop style hum. Dragonfly does not exhibit this when not used in Pi. I have tried attaching the Dragonfly to an external powered USB hub to help with power issues / noise, but issue remains

So the questions is, am I (as i suspect i am), asking too much of the Pi to drive two outputs simultaneously which is manifesting as noise ?

I know there is a simple solution - get another Pi (or an Allo USBridge), but its not called tinkering for nothing, so i would be glad to hear opinions anyway !

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I have a DragonFly Red that exhibits similar symptoms (“background static and a repetitive machine noise interference”) when connected to a CuBox-based endpoint running Debian and the current version of RoonBridge.

I’ve fooled around with this endpoint quite a bit in an effort to resolve the problems, but they persist, and the only thing I can come up with is that there’s some kind of problem with ALSA and the current DragonFly’s.

I have a DF Black, too, and both work fine when plugged directly into a Mac or connected to an iOS device via an Apple Lightning-to-USB camera adapter. Is anyone using a DF Red or Black with a Linux-based Roon endpoint and having no problems?

It could be related to Etherent and USB sharing the interface on Raspberry Pi’s and causing a bottleneck when using both at the same time.

I’ve had up to 4 USB DACs connected to an RPi (via a powered USB 2.0 hub) at the same time and experienced no issues streaming to all four at the same time.

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Hey Paul, if you disconnect the Digi+ board (just temporarily, for a quick test) does the problem persist when playing to the DragonFly? Or it’s ONLY when the Digi+ board is connected?

And are you doing any up-sampling to the DragonFly or just bit perfect playback?

No upsampling - but perfect. Reluctant to disconnect the HAT but have disabled it in Roon and physically disconnected coax to other DAC - no change. It’s not a big issue. I may just have to find another way to use the DF (which works fine with iOS and CCK)

I’ve run multiple USB DACs on the same Pi3 with dietpi. (I didn’t know it was possible to run a HAT and USB DAC simultaneously in dietpi.)

If you haven’t done so, you might try enabling PSU noise reduction (dietpi-config > audio settings).

I’m running Rpi 3 with Hifiberry Digi+ in tandem with USB out to my Marantz HD-Dac1 without problems, upsampling to DSD64 on roopie.

This is an issue worth considering. I actually connect my DragonFly Red / RPi3 endpoint to roon via wi-fi (gasp!) and it sounds like a dream. (Tidal tracks sometimes drop, but no more often than Tidal tracks also drop via the Tidal native apps on iOS and Windows.)

If you have a strong, stable wifi, try switching the Pi to it and see what happens.

Thanks everyone - have enabled PSU noise reduction but noise remains. Might be the ethernet/usb shared bus issue, but in that case one would expect Gustav to experience the same issues. Haven’t tried the wifi option as away from home currently but may give that a try as i have strong wifi in that area. Ultimately a separate endpoint may be the solution…

I’m sorry that I wasn’t clear enough, I’m currently running this over Wifi. But might it be that my Marantz is not powered by the USB while the Dragonfly is?

Could be ! Is this wireless via a dongle or built in Rpi ?

It is the built in. I have a very good signal though.

Def going to give that a try - thanks Gustav

Got home enabled wifi - connected. Disconnected Ethernet connected and disabled - noise remains. Think I will give up and use dragonfly as my OTG dac !

Yep - as per my other post in dietpi section my issue was power - 5v 2.5a power solved everything. Thanks for advice and input as usual