Hello. I was also having a tone issue with my TT4 passive Sandberg. I definitely feel that my Sando lacks low-end compared to my Fender JMJ Mustang, P-Bass and my Rickenbacker 4003. Those other basses just have such a great low fundamental that the Sandberg doesn't have. Could this be a potentiometer issue? Stock strings? Any help from your end would be appreciated.