Bass improvements – intonation and string height

Posted by is9582 on October 21, 2015as , , , , , ,

I recorded some music a few days ago, and after creating the drums, I went back in to lay down a bass track. While I was tuning up the bass, I happened to glance at my strobe tuner and noticed the intonation was off quite a bit, so I grabbed my tools.

[**For anyone that doesn’t know about intonation on guitars and bass guitars, I’ll give a brief explaination. Most electric instruments have adjustable saddles in their bridge, which are there specifically for setting the intonation. When an open string is played, say the low E string, an E note sounds (big duh, huh?). When you pluck the string again, while pressing against the 12th fret on the same string, it also sounds an E note, but it is one octave above the open string’s note. If the intonation is not set correctly, the note at the 12th fret can be either sharp or flat, relative to the open string. By moving the bridge saddle, you can adjust it until both the open note and fretted note are precisely one octave apart, rather than just shy of an octave (if the fretted note is flat) or just over an octave (if the fretted note is sharp).]

During the adjustment of the intonation, the saddles on the E string and the A string both ran out of travel, meaning they could not adjust far enough so the two notes were exactly an octave apart. To fix this, it was necessary to move the physical bridge further away from the headstock. Since the D string and the G string both intonated with the bridge in it’s current location, it was important to make sure I didn’t move the bridge too far rearward, or I could reach the point where the D & G could no longer intonate correctly.

Bass body with paper template created.

Bass body with paper template created.

I made a paper pattern, that I fit around the bridge in it’s current location, and I taped it directly to the body of the bass. This allowed me to mark directly onto the pattern, keeping the important information close at hand, and not needing to clean up the surface of the bass when complete.

Closeup of the pattern, with notes and information.

Closeup of the pattern, with notes and information.

Once I determined the location of the bridge, I marked through the three screw holes this model has, to find where I needed to drill. The body on this bass is somewhat thin, so I made a wooden jig that prevented the bit from going deeper into the wood than I wanted, as well as helping to keep the holes perpendicular to the top of the bass. I used a small compass like an awl, to mark the precise location where I wanted each hole. On a previous test, I used a 1/8″ drill bit for these holes, and I was able to muscle the screws home, but it was just a bit more tight than I wanted. On this upgrade, I used my 9/64″ drill bit, which seems to be the perfect fit for the provided screws.

Using a small compass to create an indentation to help prevent the drill from wandering.

Using a small compass to create an indentation to help prevent the drill from wandering.

After I drilled the holes with my cordless drill (the back of this bass is curved, so it was not really an option to use the drill press), I hand-fed each screw until it bottomed out. I make sure to use a fairly fresh Phillip’s bit that fits the screw properly, which helps to prevent “camming” out or other damage to the screw’s heads. I like to pre-feed the screws, so there is less chance I’d slip (as it doesn’t require as much force, after the threads are cut in the wood, the first time) with the bridge in place, and possibly gouge the bridge.

With the bridge back in place, I strung up the strings, and set the intonation. Everything worked great, and all four strings were spot on, with room to travel if needed in the future.

As I now was certain the bridge is where it will function correctly, I decided to recess it slightly into the top of the bass, to bring the string’s action down a bit. This will serve two purposes; First it will make it easier to fret notes along the neck, but more importantly, when the string has less distance to travel, before hitting the fret, there is less chance it will cause the note to play sharp. As the string stretches (even though it isn’t much), as you press the string down to make contact with a fret, this can cause a note to go sharp, just as if you bend a note that is already fretted.

I measured the distance between the bottom of the E string and the pickup, when I fretted the string at the 24th fret, to make sure it wouldn’t make contact. (Obviously, if it did, I could also recess the pickup in the same fashion as I will do for the bridge.) I also measured to see how deep the bridge could sit into the wood, and still have access to the screws that adjust the saddles, in case a different set of strings behaved differently. Based on these measurements, it looked like the maximum depth I could recess the bridge, would be approximately 0.1″.

With the bridge screwed solidly to the bass, I used a sharp marking knife to score around all four sides. Start with a light scoring, and progressively get deeper, until you are done. I removed the bridge and set it aside, so I could remove the waste wood in between the score lines. I started this operation with a small chisel, which I used to remove the inside “lip” on all four sides. I do this so I can follow up with my router plane, and this allows me to stay a decent distance from the “good” wood, helping to prevent any accidents.

Red arrows point to the heavy scored lines against the bridge body.

Red arrows point to the heavy scored lines against the bridge body.

Make sure the iron in your router plane is as sharp as you can get it, so there is less lifting of the wood, and more pure cutting. Start with the iron set so it is just barely below the router plane’s sole. It is quite easy to overshoot the target depth, especially when the max depth is only 0.1″! Take it slow and steady, and you should end up with a professional job.

Stanley router plane, removing some of the waste inside the score lines.

Stanley router plane, removing some of the waste inside the score lines.

 

Recess complete, and waiting to re-install the bridge.

Recess complete, and waiting to re-install the bridge.

 

Bridge inserted into the shallow recess, with strings loosely laid across the pickup.

Bridge inserted into the shallow recess, with strings loosely laid across the pickup.

I stopped with the bridge approximately 0.05″ deep, and plan to play the bass like this for a while. I can always come back in and make it a little bit deeper, which is usually easier than the alternative. BUT, don’t despair if you happen to go too deep. You can find a range of materials that you could use as a thin spacer, underneath the bridge, to raise the bridge as needed.

Now that the bridge is repositioned and lowered slightly, I’ll see how it plays and decide if it feels like I should remove a little more wood from underneath the bridge. Time will tell when/if this bass is ever totally complete.

Thanks for stopping by and checking out my blog. As always, please let me know if you have any questions or comments.

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