Hi, I have a Dean Edge Hammer 4 bass and I want to replace the active pre-amp because the Bass and Treble controls aren't doing anything. I did have this checked at a guitarshop, but they couldn't find something wrong and said it's probably normal behavior... I did some research on the current configuration of the electronics in my bass and found out that it uses a RBA-04M as pre-amp. After some googleling I found the wiring diagram of this specdific pre-amp. Using this wiring diagram I noticed some anomalies in the actual configuration in my bass: The ground isn't daisy-chained between all 4 control pots, but seems to be splitted between Volume & Balance control pot and the Bass control pot & both pickups & the output jack connector. The Treble control pot isn't even connected to ground at all. --> Could this explain the malfunctioning of the Bass and Treble controls? The red+white wires of both puckups are soldered together (considering both pickups are passive humbuckers with coils connected in serial), but these 2 wires of the neck pickup are soldered together on the output pin of the jack connector and these 2 wires of the bridge pickup are soldered together and put somewhere behind a piece of tape. --> Should I remove the soldered red+white wires from the output jack connector? Using a multimeter I measured a short circuit between the output pin and the ground pin of the jack connector. --> What could be the reason of this? For me it doesn't seems very logical, because why should one put the output signal to the ground? I have done a search for a replacement of the pre-amp and the controls and I have found a Glockenklang 2 band EQ that comes with 4 control pots, the same as in my actual configuration. Can this be a good replacement for my bass? The reviews are looking good. The wiring diagram looks pretty simple, I only have to find out which wire of the pickups (green or black) is the output of the pickup that I have to connect to the Balance control pot together with the ground wires of both pickups. I hope someone with some experience in this matter can give me some advice.