The original Nashville pre (to me) seemed like it was an NTMB and a TCT spliced together with the ability to switch btwn the 2. With the volume knob pushed in you had an NTMB type voicing, just mid city (too much for me, got pretty honky). Then, if you pulled the volume knob out you got a TCT type voicing with the ability to control the mid scoop level via a mini trim pot inside the preamp cavity. I always just left my preamp in this mode with mid scoop set to minimum. It really added the right amount of warmth and clarity for what I wanted. When that preamp died, neither Gibson or Bartolini was helpful in finding me a direct replacement. Gibson just didn't care and Bartolini just wanted to sell me the new NTMB stuff. At that point Bartolini still offered a pre-wired "Burbank Tobias" preamp, but the person I talked to convinced me to spring for the HR5.4 NTMB because "the Burbank pre was a 6 week wait period due to it being a special order, hand wired unit. Plus, the HR5.4 NTMB was ready to ship today, was almost identical to the new MTD preamps and will sound as good if not better then the Burbank pre". Well he was dead wrong. The HR5.4 sounded like the stock Nashville pre without the slap tone engaged, but worse. No bass...no treble...just everything from 200Hz-1Khz. After that I just stopped playing it and almost got rid of it during a Guitar Center "trade in, trade up" deal. However, before letting it go I did some reading and realized how vastly different the TCT voicing was from the NTMB and remembered how good the bass used to sound before replacing the preamp. That was my "ah ha" moment. I then immediately called Bartolini to order that Burbank pre, but unfortunately they had discontinued it. Very disappointing news and all the Bartolini guy had to say was "if you feel like digging, the information is still out there somewhere". I then set out to track down the wiring diagrams that I knew had to be somewhere on the web since they used to be on Bartolini's website. Sure enough (via combining 3 separate diagrams) I found all the part numbers and instructions needed to wire my own Burbank TCT pre. I decided to go with an XTCT module which moves the mid cut frequency up to 500Hz (original TCT was 300Hz and then NTCT was 400Hz) because it's an updated design (should last longer/work better) and it cuts the mids at a point that helps warm/clear up the tone while leaving the "meat & potatoes" low mid frequencies intact. Now my bass has more of that classic Tobias sound than it ever has.