02-04-2022, 01:24 AM
Like everyone else that's using an external amp I've been running into the issue of noise/static/whine and was trying to get rid of it before finalizing my install. First thing I noticed was I was able to eliminate all noise when running the amp from vehicle battery and powering the RPi/buck converter from a mains DC power supply. That coincided with someone else's post which recommended this Great Scott video: https://www.youtube.com/watch?v=n_b_0BWP0mI
I followed that up with Robert's Smorgasbord to ensure I understood the implementation and added the additional filtering: https://www.youtube.com/watch?v=hVjs5LGEvLY&t=0s
That worked - sort of. I intercepted the USB sound card with isolated power and sent only the data lines to the RPi. There was a significant reduction in noise but it wasn't eliminated. This led me to look for digital isolators. Since USB is bi-directional, the chip actually has to handle packet flow, and the selection quickly narrows to Analog Devices ICs: https://www.analog.com/en/parametricsearch/11032#/
According to Amazon comments the UGreen sound card operates with 16-bit at 48Khz. This falls below USB2 "full" speed of 12Mbps. Mouser has the ADuM3160 for ~$10, but as others have already had a need for isolated power and data on USB2 devices, you can get a populated board for not much more: https://www.amazon.com/HiLetgo-ADUM3160-...BJU5WZ8J7V&keywords=adum3160&qid=1643936829&s=electronics&sprefix=adum3160%2Celectronics%2C86&sr=1-4
This worked for me, even with the amp power ran alongside the coax cables. It seems that ferrite cores, ground loop isolators, probing your chassis for different ground points, and isolated power won't solve the problem entirely as noise is still transmitted on the data lines.
I followed that up with Robert's Smorgasbord to ensure I understood the implementation and added the additional filtering: https://www.youtube.com/watch?v=hVjs5LGEvLY&t=0s
That worked - sort of. I intercepted the USB sound card with isolated power and sent only the data lines to the RPi. There was a significant reduction in noise but it wasn't eliminated. This led me to look for digital isolators. Since USB is bi-directional, the chip actually has to handle packet flow, and the selection quickly narrows to Analog Devices ICs: https://www.analog.com/en/parametricsearch/11032#/
According to Amazon comments the UGreen sound card operates with 16-bit at 48Khz. This falls below USB2 "full" speed of 12Mbps. Mouser has the ADuM3160 for ~$10, but as others have already had a need for isolated power and data on USB2 devices, you can get a populated board for not much more: https://www.amazon.com/HiLetgo-ADUM3160-...BJU5WZ8J7V&keywords=adum3160&qid=1643936829&s=electronics&sprefix=adum3160%2Celectronics%2C86&sr=1-4
This worked for me, even with the amp power ran alongside the coax cables. It seems that ferrite cores, ground loop isolators, probing your chassis for different ground points, and isolated power won't solve the problem entirely as noise is still transmitted on the data lines.