I'm troubleshooting an old solid-state bass amplifier (Ampeg B-15). The power supply has a 56 VAC transformer tap into a 4-diode full bridge rectifier circuit.
One side of the bridge goes to ground. The output side (power rail) of the bridge has 3 filter capacitors before any other circuitry: two 2500 uF electrolytic capacitors in parallel to ground and a 0.1 uF non-electrolytic in parallel going to ground.
I know the large caps are filtering caps to reduce ripple. What is the function of the 0.1 uF since it theoretically doesn't add any significant capacitance?