So, last time, we talked a little about the background on this whole string-angle at the nut thing.
To recap quickly: The angle the string takes between the nut and the tuner is important. Fender-style headstocks can have tuners placed some distance from the nut which means those strings leave the nut at a shallow angle.
And that’s a problem.
What’s the problem
The angle at which the string leaves the nut determines how much force is pulling that string down into the nut slot.
Steeper angles mean the string gets pulled down harder.
A more shallow angle… Well, that can cause some problems.
Buzzing on open string
First up, and most obvious, is that a string that’s sitting more loosely in the nut will be more inclined to buzz when played open. If you’ve a poorly slotted nut, this problem can be multiplied.
Without so much ‘pull’ down into the nut, the string’s vibration can cause it to rattle in the slot.
Lack of focus
A lack of ‘focus’ can also be a problem. A string’s vibration is the heart of the guitar or bass. Anything that interferes with that vibration can suck tone.
Without the downward pressure from a steeper angle, the vibration may cause the string to move slightly in the nut slot. Maybe this won’t be enough to cause buzz, like above, but it may well impact your tone. A looser string will tend to sustain for less time and may well play less cleanly.
Not what you want.
Guard against string angle problems
If you’ve got an instrument with string retainers, you probably don’t need to worry about this.
However that’s not a guarantee.
For example, this bass had a buzz when the 3rd string was played open. The nut height seemed ok, as did action and relief.
Pressing the string just behind the nut cured the problem. Check out the side view in the first image below. You're looking at the A string in particular.
The string angle is too shallow on the A.
This is not uncommon on Fender basses. If you don’t wind the string low enough down the tuner post (on that 3rd/A string mainly) you’ll end up with an angle that’s shallower than ideal. This may cause the problems mentioned above.
The solution is to restring and make sure to leave a couple of wraps and to keep those wraps pretty low on the post (second photo). Pretty easy answer but not something that’s terribly obvious unless you know.
Same goes for guitars. Retainers help where fitted — and the problems on the other strings tend to be less pronounced than that bass A-string — but keep an eye on your string wraps when restringing. I’d aim for about three turns on the 4th/D and around three-and-a-half to four turns on the 3rd/G.
On the other hand
By the way, it’s important to remember that the converse is also problematic. You don’t want too steep a break-angle either. Too steep an angle can encourage string breakages and isn’t great for tuning stability — especially on trem-equipped guitars.
Steeper angles make for sharper corners and kinks so don’t go overboard with this.