Coarse Tuners part 2

As described in an earlier post, I've tried to make a compact set of coarse tuners to go with the fine tuners on my Schaller 456 fine tuning bridge, so I could reduce the headstock and loose the big and heavy traditional tuners. The earlier attempt in the form of a locking nut wasn't succesful, but now I think I'm on to something.

I've installed my own coarse tuners, each consisting of a blind screw, a T-nut and an allen nut (a.k.a. an internal wrenching nut). In the blind screw, a hole is drilled for the string to go through, just like the peg of an ordinary tuner.

To tune up the guitar, you turn the blind screw clockwise with an allen key until you reach the approximate tone. Then you fasten it by tightening the allen nut on the back of the headstock. The rest of the tuning is done with the fine tuner at the bridge.

One of the beautiful things about it is that when you tighten or loosen the string by turning the set screw, the height of the string over the fingerborad stays the same, since it rests in the screw's thread. And the pull of the string tightens the allen nut against the T-nut, securing the string even more.

The best thing about it is, it seems to work perfectly. And it's much smaller and lighter than ordinary tuners, so it's a good solution if you want to build a headless guitar - or convert an existing guitar to one. You'll have to leave a little bit of headstock for the T-nuts, but that's not much. And you might want it anyway to stop your fretting hand from sliding off the neck.

On my own guitar I've mounted the tuners on the very end of the headstock. The reason is that I'll be using the other sections of the headstock for experimentation with alternatives to the T-nuts. A set of threaded inserts and a brass plate with threaded holes are some of the things I want to try. Next experiment will probably be threaded inserts mounted on the next section of the headstock. And I imagine that when I have reached the last section of the headstock, next to the nut, I'll know which of the solutions I prefer.

Drilling the string holes in the blind screws was a pain. I only got two made before I had dulled or broken my drill bits. I'll have to buy some new ones and do it right. That's the reason why the remaining four strings in the picture go to traditional tuners.

Btw, I imagine that if you add some loctite or similar to increase friction, you might be able to do away with the allen nut. Afaik, there also is a substance called "peg dope". I have to get some and try if the tuner can hold the string without the allen nut.

To-do list

Nothing much has happened on my T-beam-bass lately. I've replaced the jack connector since the old one didn't work and clamped the connecting cable going from the jack more securely to the sliding bracket. Plus, I've borrowed a friend's bass to do some comparisons of sound, feel and ergonomics.

His is a 34" bass, and though the picture doesn't really show it, mine, with its 30" scale length, is much smaller and lighter.

My bass still isn't exactly pretty, but I do intend it to be so one day. But until now (and probably some time ahead as well), most of my focus is on experimentation rather than looks.

Nevertheless, in an attempt to convey an idea of what I expect it to become some day, here's a list of some of the things, I'd like to do next:

• Make the saddles lengthwise adjustable for intonation, i.e. making slots for the saddles and fastening them with nuts.
• Shape the neck as shown on the image . I have to modify the sole plate of my jigsaw to be able to do that.
• Make a prettier and more ergonomic shield in 5 mm acrylic (that's approximately 0.2"). The current one is just 3 mm thick, and it's too fragile and flimsy looking.
  
• Make mahogany sides rather than the current spruce ones. What's keeping me back here is that I'm not quite sure yet where the holes for the shield are going to be, and I'd rather keep the mahogany intact and experiment on the spruce.
• Decide whether I like the sound of the vertical pickup. If so, I'll tidy up the bracket. If not, I'll buy a P-bass-pickup and use one half of that in a new bracket.

I am not alone

One of the good things about the T-beam bass or guitar is that it's fairly easy to build a functioning instrument and improve it from there. In spite of its relative simplicity, there's still lots of challenges in it. If you're ambitious, there's plenty of aspects to improve. If you're not, there's still the joy of building your own functioning, albeit crude instrument.

It's a really good project in many ways, but until recently, I thought I was the only one making a T-beam bass.

To my delight, as I discovered here, I am not the only one. Kaspar Torn is building one as well. It's still in its early stages, and so far, it looks very promising. As you can see from the pictures, it differs from my own project in a number of ways:

Strings are anchored in a bolt through the vertical flange

String slots and zero fret

Tuners upside down

Angled tuners

This project is going to be interesting to follow. Kaspar leaves many options open, such as a detachable acoustic body and a spike, allowing it to be played upright.

I will post updates as the project moves along.

A slightly prettier sliding bracket

I've made a sliding bracket for the small pickup. It slides with little effort and easily picks up the different antinodes of the strings. Unfortunately, the pickup itself doesn't sound that good, so one of the next steps might be mounting one half of a P-bass pickup in a similar bracket - or perhaps have two sliding brackets and the usual switching arrangement.

Trying a good, well-known pickup should give me an idea of what the instrument sounds like and make it easier to find out its particular characteristics.

The system of cable and female jack on the body also works fine. I plan to add tone and volume pots down by the jack at some point.

A body that preserves vibration

With the addition of a body to the T-beam bass, it begins to resemble an instrument.

The body is a 3 mm (around 1/8") acrylic (or plexiglass) shield, cut with a saw and an angle grinder, polished, and bent in shape with a hot air gun. As with almost everything else on the bass, it is not intended as the final version. For this, I will use thicker (probably 5 mm) acrylic sheet and have the leg rest further to the back.

The acrylic shield is slightly bowl-shaped so it follows the contours of my body. It's a fairly deep bowl shape ;-) It has a leg rest bent into the lower part and an arm rest created by folding back a wing on the upper part. It quite looks like the body of an Ovation Breadwinner, though that was not the intention originally. It's very comfortable, and I expect it to be even more so when I've moved back the leg rest.

The four mounting supports that connect the shield to the stick will have to be replaced with a central support mounted on one of the two places where the stick has least vibration. A so-called node. I located the node by suspending the stick on two springy foam blocks, pouring salt on the stick and tapping it with a knife handle. As predicted in the marimba literature, the salt would gather to show the location of the node. Luckily, the node is somewhere in between the mounting supports, which makes construction easy. BTW; marimba and vibraphone builders do a lot of interesting research into the acoustics and vibration of wood; something that the guitar builders might draw upon in their work.

The reason for having the shield mounts on the node is to preserve vibration in the stick and not have it travel through the body and into the all-absorbing torso of the player. The node does not vibrate - or at least it vibrates less than other areas of the stick, meaning that less vibrations will be transferred from this point to the shield than from any other areas. I expect it to have a pronounced effect on sustain, and perhaps also on tone.

Some sort of leaf spring suspension mount might give even better isolation between the shield and the stick, but that will have to wait for a later version.

A sliding pickup

There has been several attempts - by for example Westone and more recently Norton Guitars - to make a pickup that can be moved to the areas of the strings where different antinodes and their corresponding overtones are located. This gives you the sound of a neck pickup, a bridge pickup and everything in between. Though only one at a time.

The T-beam bass and the bracket for the humbucker pickup were too obvious a candidate to not trying something like this. And since I allow myself an impulsive and unstructured approach to my hobbies, I gave it a try.

The pickup bracket has nylon cable clips screwed to it. The clips grip the edge of the T-beam top flange and allows the whole thing to be slid easily along the beam. It was necessary to isolate the pickup from the vibrations of the guitar body (hence the rubber bands and foam padding). If not, the vibration characteristics of the string on the pickup's location would be hardly audible compared to the much stronger body vibrations also received by the pickup. Isolating the pickup also significantly reduced the noise of the nylon clips sliding along the T-beam... nice, because now it is possible to slide the pickup "in-tone" and hear the subtle changes of the timbre of the string.

The bracket and pickup is big and heavy, so one of the next steps will be making a sliding bracket for the much smaller between-strings pickup, which I made earlier. The small pickup should also be better at sensing a small section of the string, where the humbucker due to its length picks up a lot of vibrations - including the unwanted ones. With the big pickup, you can easily hear the difference up and down the strings, but the effect isn't exactly striking. I hope and believe that the small one will do a better job.

I had to rout a channel in the wooden sides for the nylon clips. With everything on, in the afternoon sun, it looks like this:

A vertical pickup

I made a pickup that sits vertically between the strings. Since the bass is two stringed, the pickup picks up one string from each side. It works well, but I have to keep it towards the bridge end, otherwise the strings will hit it.

It is made from an acrylic sewing machine bobbin wound (on a sewing machine) with a very thin copper wire: 0,05 mm which is somewhere in the neighbourhood of AWG44. This wire is thin as human hair and very prone to snapping... it happened more than once, but I've learned to handle the delicate wire.

I measured the DC resistance to 2,3 Kilo Ohm. I'm not sure how much I can deduct about its impedance from that information, but it's only around one fourth of the resistance of the humbucker that I used earlier.

The center of the bobbin contains a stack of small neodymium magnet discs and iron cylinders. This allows me to vary the magnetic force by replacing an iron disc with a magnet if I want it stronger - and vice versa, of course.

I can rest my hand on the pickup while playing, but sometimes it's in my way. Still, I usually find my way around it and I really like the simplicity of having one small coil picking up both strings. I might recess it a bit into the aluminium and I might abandon it in favour of a more traditional pickup, but overall, I'm quite satisfied.

BTW, I also made two tuning screws from ordinary screws fixed in oak dowels with epoxy glue. They have just adequate friction against the fingers, but they'll have to do until I get a couple of knurled nuts. Still, compared to using a screwdriver when tuning, it's a great improvement.