JLP
. . . because we are looking at a set of measurements (nut height/relief/bridge height) to quantify what you have been feeling.
And . . . as you are playing with a light touch, you would not tend to 'induce' as much buzz as some of our more ham-handed friends.
Plus . . . adjusting the truss rods IS changing the string heights in a reverse fashion to raising/lowering your bridge. In other words, you're doing it from the nut end instead of the bridge.
Visualise that as you tighten the truss rods, the nut is going to go down relative to the body as the neck flattens out (or down), and the middle of the fingerboard rises. Loosen it, the reverse happens: The nut will go up relative to the body as the fingerboard bends up at each end, and the middle of the fingerboard sinks.
But remember this is happening in SLIGHT fractions of an inch. I have to use rules or feeler guages to record these changes as my eyes can't see these slight changes.
Over time, these slight adjustments back and forth + time usually end up where you are now.
Probably NOTHING has changed, it's just cumulative over time, especially if the rods were the only thing you've changed. Different strings tune up to different lbs/ft in the total pull of the four strings from brand to brand and guage to gauge.
In set up I go at it this way:
1. TUNE to pitch.
2. I check the nut/string heights.
3. I check the neck relief.
4. I check the string heights over the last fret.
Because...
TUNING equals tension on the neck. Must be correct: Sharp, too much pull. Flat, too little pull. We tune constantly doing this is we make any adjustments to keep the pull consisitent.
NUT HEIGHTS have to be right: Too low, buzz on open strings and/or the first couple frets. Too high, makes the action harder, can throw tuning off as you're bending notes just to fret a note.
NECK RELIEF I'm looking to get it dead straight, then let it off just enough so it won't buzz through the amp, even if I get a little buzz here and there unplugged. Some basses will play fine with a dead straight neck, some won't.
HEIGHTS OVER THE LAST FRET I'm looking to set the height of each string the same so the strings FOLLOW the radius of the fingerboard and bridge saddles. This set of heights will raise and lower to kill any remaining buzzes they introduce.
And these measurements vary from as low and flat as humanly possible if you want it as low as Entwistle, to higher numbers depending on what feels good to YOU: The only numbers that matter here. There's no two identical setups as there are no two identical players.
The general setup would be
NUT HEIGHT Fret each string at the third fret. Reach around with your other hand and fret the same string at the first fret while still holding it down at the third. You should feel a little movement and hear a 'tink' as the string bumps into the first fret. If it's already touching, raise it slightly. If you think it's a lot of travel lower it slightly. In real numbers, it's like 20/1000ths under the G and 30 to 35/100ths under the E over the first fret, unfretted, in that neighborhood.
NECK RELIEF Capo the strings down at the first fret. Fret the
E then the G about where the neck meets the body. Around the 10th or 11th fret, you should have enough clearance to slip in a thin to medium pick. Not enough, back off the rod slightly. Too much, tighten it slightly. Again in real numbers 10 to 15/1000ths relief for Entwistle, more for most of us.
HEIGHT OVER THE LAST FRET should be around an 1/8 of an inch. In real life, you will probably run the bass side that high or a bit higher and the treble side a bit lower: The big strings flop around more than the D and G. In fact, the nut will probably mirror this lower/taller, higher/shorter profile.
This is the basic layout. Their is an interaction of the three that can make you NUTS till you 'get it'. Or just take it to a qualified tech, and spend your free time on less aggravating endeavors ! ! A lot of times, I wish I had! But should you teach yourself to do this, then as you search for your perfect string set, you can make the bass feel the same from brand to brand, if that's important to you.
And should you decide to dive in, I can not stress enough to make adjustments in TINY amounts: Think watchmaking, not engine rebuilding. And to constantly check your tuning to maintain the correct tension.
It's all up to what's right for you.
J o e y