Low action - Peavey Millenium 4 string bxp bass

It seems that your neck has straightened itself or produced a bit of negative bow. That's about all that can change by itself. Except it usually happens as it gets warmer, not colder. Oh well, if you were in Australia for instance, it would be warmer now, but not up here.

Anyhow, you can loosen the truss rod at "2" to produce a little positive bow. I don't think that would be my first choice, but it depends on the temperature where you are. Sight down the neck and see if it is sunken in the middle, which is a good thing. Or is it straight and humped up? If straight and not bowed, you create the bow and higher action by loosening all strings, loosening the neck at the neck plate, 4 screws on the back, and raising the heel of the neck till you can see and adjust the truss rod, with maybe a half turn counter clockwise. Then tighten the neck to the body (firmly snug only, not over-tight) and re-tune. The strings should pull the neck into place, with a little higher action. If the adjustment was sufficient, the buzz could be gone.

I really don't know why else your neck would change it's bow and cause the buzzing, in the lower registers, as you said. So I point to the saddle adjustment screw at "1", which I would probably tighten, 2 per saddle till the saddle is high enough, just a fraction more, to reduce the possibility of buzzing everywhere on a given string. For that, you loosen the string, and turn saddle screws very slightly clockwise. Then, tune the string, and see what you got! :D

The neck may not be in actual negative bow but just less positive bow (getting closer to being flat). It happens as the seasons change. Depending on where you are located and the climate there will determine which seasons you get the neck giving more relief. Where I am (northern California) the weather gets moister in the fall and so with more humidity the neck straightens out more and I need to tighten the truss rod to bring back some more relief. In colder climates the air gets dryer in the fall and the neck gets more relief and the truss rod may need to be loosened.

Why you didn't see this before is that before you had the setup done and the action lowered the changes in the relief due to the seasons was not enough to cause the high action setup strings to buzz. So, you action hasn't changed over the 6 months only the relief in the neck.

Thanks guys, I will give this a try when I'm feeling confident in my hands here. Just so I'm clear, if the neck is coming up to be straight and flatter then I loosen the truss rod? should I try and adjust the bridge first? I'm hesistant to make any truss rod changes.

Just to add, I live in northern california in the foothills, about 2500 ft. Mild to cold fall with some humidity. I'm really bad about keeping my bass in it's case too because I can't keep my hands off of it :lol:

Thanks guys, I will give this a try when I'm feeling confident in my hands here. Just so I'm clear, if the neck is coming up to be straight and flatter then I loosen the truss rod? should I try and adjust the bridge first? I'm hesistant to make any truss rod changes.

Just to add, I live in northern california in the foothills, about 2500 ft. Mild to cold fall with some humidity. I'm really bad about keeping my bass in it's case too because I can't keep my hands off of it :lol:

So, your bass' neck condition would be similar to what is being experienced by Hyperborea, and he knows how, and is dealing with some humidity issues too.

Humidity expands the wood, or fattens up its molecules the same as heat, though we're not going to get into 'dry heat' or any disagreement.

I think we agree that the neck straightening itself is causing your buzz :shock: so it looks like you may have to loosen the truss rod.

Thanks guys, I will give this a try when I'm feeling confident in my hands here. Just so I'm clear, if the neck is coming up to be straight and flatter then I loosen the truss rod? should I try and adjust the bridge first? I'm hesistant to make any truss rod changes.

Unless there's some other reason to suspect that the action needs adjusted then it's probably just fine and won't need adjusted. From what you've described it's probably the neck relief that needs changed and that means adjusting the truss rod. It can be a bit scary but if you take it carefully and do it gently and gradually then there shouldn't be any problem. If you really feel that you can't do it then you could always take it back to the tech/luthier who did the setup. This would probably only be 10 minutes of his time and not too many dollars.

If you do want to do it yourself it's not too hard. The setup for a bass is identical to that of the guitar except that the target settings (neck relief and string height) will be different. I don't know of any good bass guitar setup sites so maybe somebody else could post one?
Just to add, I live in northern california in the foothills, about 2500 ft. Mild to cold fall with some humidity. I'm really bad about keeping my bass in it's case too because I can't keep my hands off of it :lol:

I'm in the SF Bay Area and the rains have started early this year and the dampness has started causing some buzzing in the guitars. I've already tweaked the guitar I've been playing the most lately. The others will get done as they come into rotation.

Don't be scared of a truss rod adjustment, just take it slow. I recently straightened the neck on a Peavey T-20 bass that took an unbelievable number of turns on the truss rod to straighten. The first day I tightened the truss rod 1 full turn, a few days later I tightened it another full turn, then I tightened it about half a turn a day for about a week straight and finally an eighth turn a day for another week. In the beginning I had over 1/4" bow when I laid a straight edge on the frets. By the time I finished it was straight and I needed to lower the bridge end of the neck a bit because of a buzz. Good luck, and take it slow.

Okay, I think I'm going to take this one on. I checked it out last night and the neck is definitely pretty straight. So a counter-clockwise turn will loosen the truss rod and bring relief to the neck, am I correct?

Okay, I think I'm going to take this one on. I checked it out last night and the neck is definitely pretty straight. So a counter-clockwise turn will loosen the truss rod and bring relief to the neck, am I correct?

Yes, CCW is to loosen the truss rod. Take it easy and turn only about 1/4 of a turn at most each time. It may need a bit of tugging to get it to start to turn but it shouldn't require any real strain - if it does it may be best to check with your tech/luthier. On a guitar what you want is about 0.008" of relief. You measure this by putting a capo on the first fret, fretting a note on the 6th string where the neck joins the body, and then measuring at the 7th fret with feeler gauges. If you don't have those a playing card is about 0.010" thick but feeler gauges are cheap and you'll use them twice a year to adjust the relief. For the bass you may want a different amount of relief.

After adjusting the truss rod give it a minute or two to settle and then measure before turning the truss rod again. After 3 adjustments or you get a measurement you like then leave it overnight to let it settle and check again the next day.