Allo BOSS DAC+RPi3+iPower = buzz/hum left channel

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
iFi has also published some guidelines and background info related to grounding, noise, hum etc.

Accessory – Groundhog

Obviously I'd never buy these groundhog devices. Still the message behind it makes sense. And you'll see that they are aware of your issues.


I usually use these Wago terminals and free-air wiring to establish quickly a common ground towards all devices/connections for trouble shooting/optimizations.
In my final setups pretty much everything gets soldered. Getting rid of all the plugs and jacks gives a nice performance boost I for sure don't want to miss.
Beside that by soldering everything I get rid of potential sources of (short/long term) problems. And I save a hell lot of money. ;)

Good luck with your project.
 
Last edited:
Thanks for the iFi links. I'd actually read that, and I do have experience with building power amps, phono preamps, etc. that work with no hum. I'm embarrassed that I didn't think of testing whether shorting the pcb ground trace to the metal chassis would kill the buzz. That would have been useful. I did try grounding the left channel signal ground to mains earth. I'm still not sure why that didn't work.

I'll drill a little hole in a chassis panel and mount a ground post to it, then solder a flexible wire from there to pin 1 (ground) on the input jack. That will ensure a ground connection from the pcb to the metal chassis. After that, it's up to whatever power supplies, DACs, etc. to have their own ground connections.

Thanks for your input on this problem.
--
 
Last edited:
Will it ever end?

Well, last night's experiments resulted in another mystery.

On the Objective2 headphone amp:

I found pin 1 on the input jack, which connects straight to the pcb ground plane.
I soldered one end of a short wire to that pin, soldered a grounding tab to the other end, stripped a bit of anodization away from one of the screw holes on the chassis, and connected the wire to that for chassis ground.

When I connect the pcb ground to chassis, the left channel no longer plays audio. I only get two channels playing with no connection from pcb ground to chassis. Now, why on earth would that be? Could it be a faulty input jack?

I was thinking that the Raspberry Pi+BOSS DAC might be the source of the grounding problem. However, it doesn't matter which audio source I connect to the input jack on the O2 amp. The behavior remains the same. So the RPi+BOSS DAC combo is exonerated.

The result is that grounding the O2 pcb ground to its chassis would not have fixed the buzz in the left channel from the iPower. I'm right back where I started.

The strangest thing is that with the Canakit psu there is no buzz in the audio output, even with the suspect grounding. If I crank up the volume on the O2 amp with cans on I can hear a tiny bit of hum, but it's smooth and low frequency, not a ratty buzz.
--
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.