Hi,
for a University Project, I designed a custom Audio Adaptor Board (based on the official Audio Adaptor Board Rev C). With the second revision of my PCB, I face the following Problem: when touching the mic input (at high gains), the board goes into some sort of self-oscillation/feedback. Without any speaker or microphone connected. Probably the mic input is electromagnetically coupling with the line output. If I remove the 2.2k Mic Bias Resistor the problem disappears. Any hints on avoiding this problem when designing the PCB? If you want, I can send you the KiCad Project.
Best,
Pascal
for a University Project, I designed a custom Audio Adaptor Board (based on the official Audio Adaptor Board Rev C). With the second revision of my PCB, I face the following Problem: when touching the mic input (at high gains), the board goes into some sort of self-oscillation/feedback. Without any speaker or microphone connected. Probably the mic input is electromagnetically coupling with the line output. If I remove the 2.2k Mic Bias Resistor the problem disappears. Any hints on avoiding this problem when designing the PCB? If you want, I can send you the KiCad Project.
Best,
Pascal