[Problem] Sound hum through O2 DAC

[chinthaka]

Hi,
I recently tried MoodeAudio. I have a sound quality problem when I am using the following setup.
Rasberry Pi 3+
Massdrop O2 + SDAC ( version of JDS Labs Objective 2 ODAC) (This has both DAX and the headphone amplifier)
Songs are in USB flash drive connected to Pi.
Connected the DAC using USB mode.

I hear a small hum sound coming from headphones when I am using the above setup. Hum is not there when nothing is playing. Only when a song starts to play hum comes. I do not hear such hum when I am using the same setup with Kodi with LibreElec. I tried several headphones different USB cables for power and connection between DAC, but same problem exists.

I have another DAC/AMP for my bookshelf speakers, but no problem with the sound quality on that. I do not have this problem when the same DAC is connected to a laptop using USB.

Could you please help me to figure out what makes this hum? This makes me Moode not usable with my headphones.

[CallMeMike]

Hi,
I recently tried MoodeAudio. I have a sound quality problem when I am using the following setup.
Rasberry Pi 3+
Massdrop O2 + SDAC ( version of JDS Labs Objective 2 ODAC) (This has both DAX and the headphone amplifier)
Songs are in USB flash drive connected to Pi.
Connected the DAC using USB mode.

I hear a small hum sound coming from headphones when I am using the above setup. Hum is not there when nothing is playing. Only when a song starts to play hum comes. I do not hear such hum when I am using the same setup with Kodi with LibreElec. I tried several headphones different USB cables for power and connection between DAC, but same problem exists.

I have another DAC/AMP for my bookshelf speakers, but no problem with the sound quality on that. I do not have this problem when the same DAC is connected to a laptop using USB.

Could you please help me to figure out what makes this hum? This makes me Moode not usable with my headphones.

Do you have the same 'hum' when you use the LINE OUT phono ports (at the back of the O2 DAC/AMP) connected directly to an amplifier wih loudspeakers?

[chinthaka]

Hi Mike,
I connected the LINE OUT of O2 DAC to 3.5mm (using RCA to 3.5 cable) IN of my other amp which is connected to the bookshelves.( I do not have a main amp with RCA IN)
I do not hear a significant hum as with the Headphones in that case. I hear a very small noise from speakers but that is insignificant and also it is there when the song is not playing.
If I plug in my headphones at the same time, I can still hear the annoying noise when songs are played.

What do you think the cause would be?

[CallMeMike]

Hi Mike,
I connected the LINE OUT of O2 DAC to 3.5mm (using RCA to 3.5 cable) IN of my other amp which is connected to the bookshelves.( I do not have a main amp with RCA IN)
I do not hear a significant hum as with the Headphones in that case. I hear a very small noise from speakers but that is insignificant and also it is there when the song is not playing.
If I plug in my headphones at the same time, I can still hear the annoying noise when songs are played.

What do you think the cause would be?

Your experiment would lead to the idea that the hum is caused by the hardware rather than the software... but then the fact that Kodi is fine in the initial set-up spoils the conclusion!

- My RPi/Moode kit is in bits now (experimenting with a new PSU) so I cannot check whether the USB fix is still available in Moode 4.3. Turn on the USB (UAC2) feature (I believe you may find it in MPD settings).

- I would not discard the idea of an issue with the O2 DAC PSU (yes... LibreElec works)

 Is the 'hum' appearing while playing any music file (mp3, flac 16-24 bit/ 44.1-192.4 KHz)...?