And here we have a solid 160W solid-state bass amp with an RCA input on the front. this amp was brought to me with the complaint of really low volume on the RCA input. upon further inspection, this definitely seemed to be true. a reasonable listening volume could be obtained with the volume knob all the way up. definitely not a practical option if attempting to play live.
looking over the schematic (this one being Revision I) you’ve got 22k resistors at each input (left and right) mixed together for mono delivery into a 33k resistor all before the first gain stage. that’s definitely a hefty signal drop. to boost the signal, i simply removed the 33k SMD resistor on the preamp board pictured below and replaced it with a small piece of copper wire between the pads resulting in a significant volume boost. cranking up the tweeter pad on the back basically turned a mediocre bass amp into a portable DJ amp.
and if you’re not familiar with solder surface mount devices, you should really check out this extremely informative video.