Audio interference - Ground Loop - Power Supply - Issues

Help and Support Help
1

Hello,

Hopefully this is in the right place - I’ve also posted this over at the RPi forums.

I’m in the process of making a Raspberry Pi based “boombox” running Volumio. From a software POV this all works great.

My issue lies with audio interference which seems to be related to power. Hopefully someone can point me in the right direction to correct it.

I’m using the following hardware

Raspberry Pi Model B rev2 (512MB)
CM108 based USB Soundcard - Link
VMA2012 Amplifier - 5V - Link
3.5mm audio cable
Pair of Creative speakers (probably not relevant)

A few scenarios I have tried and their results:

Power Supply - HTC 5V/1A or EasyAcc 5 port or Asus 5V/2A
Ethernet connected
Amplifier powered via 5V/GND on RPi GPIO pins
Result: Lots of noise when powered up. Noise seems to link to CPU/Ethernet activity.
Other: When GND is removed the amp stays powered but the noise increases in volume, if 3.5mm cable is then removed amp is powered off (ground loop through 3.5mm cable?).

Power Supply - 12V/2A through 5V converter
Ethernet connected
Amplifier connected direct to the 5V conveter
Result: Identical to scenario 1 - including the removal of ground and the amplifier still being powered.

Power Supply - 12V/2A through 5V converter
Ethernet connected
Amplifier connected to a separate 5V converter which is connected to the same 12V supply.
Result: Identical to scenario 1 - including the removal of ground and the amplifier still being powered.

Power supply - HTC 5V/1A or Asus 5V/2A
Ethernet connected
Amplifier connected to 4xAA rechargeable batteries - totally separate power supply.
Result: No noise at all.

Power supply - HTC 5V/1A or Asus 5V/2A
Ethernet connected
Amplifier connected to totally separate 5V/1.2A power supply.
Result: No noise at all.

Realistically I do not want to use a different power supply for the RPi and Amp.

I don’t mind using the 12V supply and having two 5V converters if it is reasonably easy to isolate them so there’s no interference across them or ground loops (if that’s the issue here).

Do I need a load of ferrite cores?

2

Read somewhere that the best power supply for the rpi was an apple charger. Also the Ethernet connection can produce a bit of noise, so would be interesting if you could test with wireless network connection as well.

Sent fra min Nexus 5 via Tapatalk

3

The ethernet may produce noise if you have ground connections, because you can get ground loops not only through PSU but also through ethernet shielding.
In my apartment I have no wall sockets with ground connection (except in bathroom and kitchen), and I notice a very clean sound. Take out the ground connection in all your equipment and try again…

4

I’ve seen very good things about this unit to filter noisy power sources:
amazon.com/Type-Outlet-Mount … B000OF4R8C

This will not solve ground loop issues. Best way to avoid those is to make sure that all of the gear connected to your rig - amp, powered speakers, etc. etc. are all connected to the same circuit.

If you can’t do this, you’ll need to invest in some ground loop isolators.

Something like this might do the trick:
monoprice.com/Product?c_id=1 … 1&format=2