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USB to I2S bridge + DAC - USB noise - power - what to deal with

jmf11

Active Member
Joined
Mar 25, 2023
Messages
101
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Location
France - Aix en Provence
Hello,

I'm working on a multichannel USB to I2S bridged based on stm32 and a simple multi-channel DAS (exES9080). Project is there: https://www.diyaudio.com/community/...lti-channel-hardware-part.414128/post-7735757.

Browsing the forums, I see that many pay some attention to the noise propagation between the USB (especially in case of USB powering the device), and the analog part.

I'm not looking at the ultimate performance, but doing it right and addressing well at least the first order items. I understand that noise from USB can creep from VBus power, and data lines. I'm looking for information on the orders of magnitude of the different contributors and "noise path" to the DAC output. Intention is to tackle the most important things first.

I understand that first of all I need high PSSR LDO for the different parts: MCU, clocks, DAC

Example: it may not make sense to have dedicated power supply for the module if noise from USB data lines or onboard MCU are on par with noise from Power rail...

Would it make sense to have a dedicated basic switching power supply compared to using the convinient Vbus 5V? Will what I will get from a phone charger be better from the Vbus 5V?

Once VDD is done correctly, what couls be the expected impact of digital isolators on data lines to the DAC?

Are there some important noise passive filtering not to miss in the system?

Documents, studies, measurements, advices warmly welcomed.

Best regards,

JMF
 
Nearly all noise with USB devices is caused by ground loops.

Ask yourself this; If the power supply in a PC was *that* noisy, do you think the CPU & GPU running Ghz speeds would be stable?

If you have noise issues, then you need a good USB isolator.
 
Hello,

I'm working on a multichannel USB to I2S bridged based on stm32 and a simple multi-channel DAS (exES9080). Project is there: https://www.diyaudio.com/community/...lti-channel-hardware-part.414128/post-7735757.

Browsing the forums, I see that many pay some attention to the noise propagation between the USB (especially in case of USB powering the device), and the analog part.

I'm not looking at the ultimate performance, but doing it right and addressing well at least the first order items. I understand that noise from USB can creep from VBus power, and data lines. I'm looking for information on the orders of magnitude of the different contributors and "noise path" to the DAC output. Intention is to tackle the most important things first.

I understand that first of all I need high PSSR LDO for the different parts: MCU, clocks, DAC

Example: it may not make sense to have dedicated power supply for the module if noise from USB data lines or onboard MCU are on par with noise from Power rail...

Would it make sense to have a dedicated basic switching power supply compared to using the convinient Vbus 5V? Will what I will get from a phone charger be better from the Vbus 5V?

Once VDD is done correctly, what couls be the expected impact of digital isolators on data lines to the DAC?

Are there some important noise passive filtering not to miss in the system?

Documents, studies, measurements, advices warmly welcomed.

Best regards,

JMF
Wouldn't it be easier to use a current XMOS chip, eg the XU316? In addition to libraries and documentation, there should be plenty of support in the relevant forums.
 
Wouldn't it be easier to use a current XMOS chip, eg the XU316? In addition to libraries and documentation, there should be plenty of support in the relevant forums.
I had in mind that XMOS was not super DIY friendly. I may be wrong. Stm32 has all needed features for a good USB to I2S multichannel bridge. I like the idea to use a general purpose MCU. And I already invested time in the ecosystem. So I'll continue that way.

I never had issues up to now with ground loops. So the question is to make up my mind about adequate management of USB noise on the system, and more especially the DAC.

The answer of danwhy here shows that TOP performance can be achieved without exotic things. Really good :)

JMF
 
I never had issues up to now with ground loops
Ground loops are caused by external factors to your project. As already said here, a standard USB isolator will fix the issue, anyone can add it to his chain if needed. IMO a plain USB-I2S adapter does not need any isolator integrated onboard.
 
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