There is no C6 on the PL0171 but you could add one easily enough. Locate both of the R30 resistors, they are 270 Ohm resistors tied on one end to the junction of R24 (10K), C9 (.01), C13 (120pf), R25 (100K), and R37 (12K). On the other end is ground. Visually, they are both alongside R18 (3.3K) in the upper 1/3 of the board, kind of right below the pair of C4 and C5 (220 pf) input filter caps.
Lift the side of R30 going to ground and put the positive leg of the 470 mfd capacitor on the resistor and the negative leg of the capacitor to the ground location.
Try that and let us know if it helps the bottom end.