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So a friend is having noise issues in his modular synthesizer. Parts of the system have LEDs driven with PWM at 6 to 10kHz, visible on the power bus with an oscope. The power line fluctuations from the LEDs can be heard elsewhere in the system on the outputs of two filters which include some high gain stages in their signal path.
I'm guessing that the modules/subsystems causing the noise have inadequate power supply bypassing (it seems often overlooked in these sort of designs). But rather than try to track down and fix the offenders individually, since it's only a problem for these two filter modules I thought perhaps some pi filters on their power inputs would help remedy the noise.
My question is, for adding pi filters to a bipolar supply, would they be arranged as in A or B below? Also if I'm way off base here, and anyone has some better ideas for me, I'm all ears.
I'm guessing that the modules/subsystems causing the noise have inadequate power supply bypassing (it seems often overlooked in these sort of designs). But rather than try to track down and fix the offenders individually, since it's only a problem for these two filter modules I thought perhaps some pi filters on their power inputs would help remedy the noise.
My question is, for adding pi filters to a bipolar supply, would they be arranged as in A or B below? Also if I'm way off base here, and anyone has some better ideas for me, I'm all ears.
