I've got power supply (transformer based) 9V powering modelling guitar effect processor. That noise gets amplified and it hurts.
Humming noise is 100Hz rectified mains. Processor takes 300mA 9V (500mA rated). Unfortunately I cannot tell ripple voltage (don't have an oscilloscope).
Is there any equation for calculating capacitance needed to eliminate the noise?
When I was studying step-up/down switching regulator IC datasheets, I saw the formula: coef**current*time_on/Ripple_voltage. But is contains coefficient, which is different from datasheet to datasheet.