Welcome to mixed signal design. There are a lot of challenges to this. The opa1642 needs
Well filtered supplies but also the high impedance side of things need to be well shielded from the digital noise generated by the USB side of things. I have not checked out the usb version of a bm800. I suspect it works but probably doesn’t have a good S/N ratio ?
Best Regards,
Jules Ryckebusch?
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On Nov 12, 2024, at 20:01, Timothy Aguana via groups.io <lolnetian@...> wrote:
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Hello,
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To provided an update to this DIY project, I've made an initial implementation with mixed results: The amplification scheme does work and the quality of the microphone output was good.
However, due to poor trace layout and bad choice in microphone body termination (XLR instead of USB-B) high pitched digital noise comes through either from cross talk between the power rails and output audio signal, poor A/D converter performance and ad-hoc modifications to the input port of the soundboard. This digital noise was also observed to increase in loudness as the resistance of the potentiometer (and therefore the gain) increases which leads me to believe that cross-talk is the main issue with the design. I've since made improvements to the trace layout and added decoupling capacitors to the rails of the converter and the OPA1642 to help alleviate the noise issue present in the audible signal.
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I would like to ask if anyone has any idea on the what the internals of the USB-B version of the BM800 looks like? Particularly the connection of the USB-B port to the on-board PCB. I've tried scouring the internet for these details but information regarding this is scarce.
