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Hum with iqaudio Dac+ when paused/stopped
Hum with iqaudio Dac+ when paused/stopped
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Old 8th March 2019, 08:57 PM   #1
e_fortier is online now e_fortier  Canada
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Hum with iqaudio Dac+ when paused/stopped
Default Hum with iqaudio Dac+ when paused/stopped

Hi,


I bought a few years back two IqAudio Dac+ along with the latest Pi available back then, the Pi 2B. Everything is great except for the following;


I'm getting some loud hum when I pause the music or stop it. The hum comes in after about 2 seconds once I pause or stop the music through MoOde. Please note that as soon as the music is playing the hum goes away immediately and the system becomes very quiet. It's almost like I would have to mute the DAC when no signal is present.


I have 2 set-up, both using the same Pi and DAC but one of them has a very low noise regulated +5Vdc and the other one using a regular 5Vdc SMPS.


Both units have the same issue. I have MoOde 3.1 installed and previously had Volumio, regardless of the software being used the issue remains.


This was my first introduction to Pi based music server so I thaught some noise was kind of normal but it's definitely too loud.


Does anyone know what can be causing this and how to resolve it ?


Thanks a lot for any help.


BR,
Eric
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Old 9th March 2019, 12:11 AM   #2
Indiglo is offline Indiglo  Australia
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Are you listening via the rca connections to an amplifier or with headphones via the 3.5mm socket ?

Try disconnecting the dac from your amplifier and listen with headphones plugged into the 3.5mm socket if possible. This will at least narrow down the source of the hum.

You may have some type of ground loop between your dac/RPi and your amplifier.
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Old 9th March 2019, 01:56 AM   #3
e_fortier is online now e_fortier  Canada
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Hum with iqaudio Dac+ when paused/stopped
Thanks for your help.

I’m listening via the rca connections to an amplifier.

I disconnected the dac from my amplifier and listen with headphones plugged into the 3.5mm socket Results: Hum completely gone when pausing and/or stopping music

You are correct, I probably have some type of ground loop between my dac/RPi and the amplifier.

What I don’t understand is when I play music and there is a pause in the music (quiet passage) there is no noise whatsoever. If I had a ground loop I would Have noise constantly.

Eric
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Old 9th March 2019, 02:12 AM   #4
Indiglo is offline Indiglo  Australia
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Yes, that's strange. I don't know what inputs there are available on your amplifier but maybe there is some type of automatic gain control taking place ?

What I mean if there is no audio input the amplifier will increase it's gain, thus making the hum more noticable, when there is audio the gain will automatically reduce to maintain the same volume level. Hope this makes sense.
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Old 9th March 2019, 09:44 AM   #5
CallMeMike is offline CallMeMike  United Kingdom
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Quote:
Originally Posted by e_fortier View Post
.....snip..........I disconnected the dac from my amplifier and listen with headphones plugged into the 3.5mm socket Results: Hum completely gone when pausing and/or stopping music

You are correct, I probably have some type of ground loop between my dac/RPi and the amplifier.

What I donít understand is when I play music and there is a pause in the music (quiet passage) there is no noise whatsoever. If I had a ground loop I would Have noise constantly.

Eric
Testing to narrow the faulty side: swap the RCA-to-RCA cable ends at the amp's side >>> if the 'hum' moves to the other channel the falt is DAC side... if the 'hum' stays on the 'original' channel the problem is on the amp side A follow-up test: if you have a 3.5mm-to-2x female RCA adaptor (or a 3.5mm-to-2x male RCA cable) you could test your amp non-MM or MC phono inputs knowing that there's no 'hum' produced via the DAC's HP OUT...etc.
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