Can you bypass a Rectifier diode from AC to DC
Check polarity twice before power on to avoid poof



The active 2 of 4 bridge diodes are shown for instructional purpose that are internal to bridge with silkscreen on part usually |~ + - ~|

If you choose to put in DC , you can bypass bridge to gain 1.5~2V  and connect regulated 20V directly to +/-Cap nodes and 0V.  

Twist short 3 heavy gauge wires for better performance (from interference).
If you get distortion at high power bass, then the Caps or power source is too small and may need to supply Amps or better filtered (if hums) with >50mF vs 10mF on board.  If Pre-Amp hums ensure good grounding, shielding.