Raspberry Pi noisey USB audio

[Jerms]

I've been putting up with a small amount of noise from my Pi3 whilst playing audio through my CM6206LX USB soundcard.

I found a work around that made my Redbear WIFI addon to work better with my Pi zero. So that got drafted for audio duties.

The problem is that I'm getting more "processor/processing" type noises through to the speakers. far more than with the Pi3.

I'm wondering if there is a reasonable (and dead cheap) way to improve matters.

I've looked at USB audio isolators and one of those may do the job. However, even cheaper would be if hacking up a USB cable allowed me to run the data lines only from the Pi and run the sound card from a hub or a separate mains PSU.

Has this approach been used successfully by anyone?

J.

[sgrossklass]

It may work out under very specific circumstances. USB data line potentials have to be within [GND, +5V], and in a setup like yours stuff could be floating all over the place. Both sides of this USB connection would need to have individual grounding.

The actually problematic part of your setup is the connection between soundcard output and amplifier, and you didn't state anything about that. Something with a balanced input would make solving the problem quite inexpensive. You can also add an isolation transformer to the list of possible solutions, just be aware that these may have pretty specific usage requirements.

[Jerms]

Amps are screwed to the back of the speaker cabs. 2xTPA3118 mono boards each. One amp per driver. (Each cab has an 8" woofer and TC9 FR driver).

Soundcard runs long RCA phono cables to each cabinet.

Soundcard is physically quite remote from the Pi. I've tried it with a powered hub too. But still get the digital birds/squirrels. Hence the question about isolating the power/gnd.

I guess I need to try it.

[DRONE7]

Soundcard runs long RCA phono cables to each cabinet.
Soundcard is physically quite remote from the Pi.

That's a recipe for noise right there...

How far is "quite remote" ?

[Jerms]

The soundcard is about 30cm from the Pi.
The RCA cables exit the soundcard away from the pi and don't come at all close to it. There are also 3.5mm jack to RCA converters but they're running in the opposite direction too.

Compared to the crap I had coming out of the Chromecast when sharing grounds with my TPA3116 this is small potatoes. It's a PITA though as I've discovered the bass drum on Simon and Garfunkel's America. It's about a 45hz thump that my smaller speaker give no hints.

1. Use laptop instead of Pi as audio player.
2. Hack USB cable and try the powered hub.

J.

[DRONE7]

I get the impression you have several components and multiple players at a number of separated locations....?
Presumably they do not all share the same mains outlet...?

To test, try plugging everything into the one outlet, even if it means running extension cords from outlet to device, and see if this makes a difference.....

I've discovered the bass drum on Simon and Garfunkel's America.

and whilst on the subject of america...

Toy Dolls... Prophetic....!?

And said goodbye to the circus
Off she went with a trumpety trump
Trump trump trump

https://www.youtube.com/watch?v=2VMNNJ2BpYw

[YashN]

Originally Posted by Jerms

I've looked at USB audio isolators and one of those may do the job. However, even cheaper would be if hacking up a USB cable allowed me to run the data lines only from the Pi and run the sound card from a hub or a separate mains PSU.

Has this approach been used successfully by anyone?

Yes, I have done this over the holidays - custom USB connector, data-only from the computer, but Ground isolation (GND needed for my DAC, not a Raspi), and injection of clean power from a DIY Linear Regulated PSU.

It's a must.

You can also combine this successfully with an AC Filter box AC-mains side for all the digital gear (Computer, etc...).