Hi, I have three J Basses with Fender Samarium Cobalt pickups. On one of those basses I recently had a repair guy swap out the existing Noll preamp for a Aguilar OPB 3 because it was just kind of dull sounding. Turns out that now it is even worse. So I compared the bass with two other J Bases I have which also have the SCN pickups. In passive mode there is a huge loss of high end in this bass. The other two sound like a normal J bass but the one in question sounds like all the treble is rolled off. When I turn on the preamp I have to boost the treble to full (16db) to get the brightness that I can get with the other preamps set flat. I don't know that much about electronics so I took it back to the repair man and he checked the wiring of the preamp and he says everything is how it should be but I know this is not normal. The bass has an ash body and a maple neck and acoustically it rings and sustains with the same level of brightness as the others. So it should sound somewhat similar.But it is world apart.It is not thin sounding so it is not a phase issue. The SCNs are hum cancelling. Is there a possibility that there is a wiring problem on the blend pot or even that maybe a lead might have come off on the pickups themselves? I'm really at a loss.