Fitting a Fishman Matrix Infinity in an Archtop Guitar

This was the first archtop guitar where I installed the FMI system:

It is a 15-inch archtop, small and comfortable to play. It has several uncommon details, for example the bridge:

Being so low, it could not have the usual adjustment wheels; instead, it has two grub screws threaded in the saddle that push onto two brass pieces embedded in the foot. This low bridge was the result of a design towards low pressure, which allowed me to make a thinner, more responsive top. You can see that there is a tailpiece, as in most archtops, but the fretboard is glued to the top, which is characteristic of flat tops:

Archtops usually have a neck extension that raises the last section of the fretboard above the top.

This low pressure design was the origin of some problems. At first, I installed a cheap piezo/preamp system with an undersaddle pickup, but I could never get a balanced volume for all the strings. I tried the obvious solutions, but nothing seemed to work. One of the problems that I saw was that the ebony saddle flexed a little under the pressure of the strings. I thought of using some kind of reinforcement or make it bigger, but first I tried to make another from a block of Granadillo wood (Dalbergia melanoxylon), which was noticeably stiffer than ebony. If you look closely with good light you’ll see that it is not the same color as the foot (Ebony):

This worked perfectly and has remained without any distortion since I made it more than a year ago, but it didn’t fix the balance problems of the saddle inside it.

Another problem was that the preamp didn’t have any controls, but I managed to wire a small thumbwheel potentiometer under the tailpiece:

As the balance problem seemed impossible to fix I left it alone for some time, thinking that any undersaddle pickup would have the same problem due to the design having such a low pressure on the piezo. I even thought that it was going to be impossible to use an undersaddle piezo, so I should better think of some other solution, perhaps an internal microphone or a different kind of piezo. However, before giving up, I decided to try a better undersaddle piezo/preamp system, so I removed the cheap unit and tried the FMI. With it, all the strings were perfectly balanced, and the tone improved dramatically. You can guess that I felt really happy. I removed the potentiometer from the tailpiece and installed the FMI controls where they were designed to be, accessible through the soundhole:

I built a small ebony adapter to flatten the inner surface of the top, but the pots can be accessed very easily due to the hole being oval. In fact, I designed it like that thinking of that possibility.

My second archtop with the FMI system was quite different:

This is a 17-inch guitar, custom designed by the client who ordered it. He had in mind what he called a “Maple and Water” theme. The inlays represent leaves dripping water that finally falls into the tailpiece. The sound holes add more to the water idea. The back and sides are quilted Maple and the top is a beautiful bear claw Spruce, both adding some kind of watery appearance to the wood. He also wanted the neck to join the body at the 16th fret, and wanted a floating pickup (Benedetto S6) as well as some kind of piezo to make it more versatile. He didn’t want to mix the piezo and the magnetic inside the guitar; instead, he would be using separate amplifiers.

He proposed to use the LRBaggs iBeam, which is a great system with a great tone, but archtop guitars are a nightmare when it comes to work inside them, and the iBeam needs to be installed inside below the bridge. I could have done it making an access port at some place, most probably the sides, but it wasn’t an elegant approach. Or I could have installed it before closing the soundbox, but this seemed to be a bad idea as contact pickups are extremely sensitive to placement. Instead, I suggested using the FMI, with its undersaddle pickup.

The first problem was where to put the control board. This was my first idea:

This way, all the controls could be accessed (the switch through the sound hole). It would need bigger thumbwheels for the pots, as they didn’t seem to protrude enough through the sides. I should also make an internal sturdy support for the board which kept it firmly in place while at the same time allowed its removal. This was perhaps the most difficult part, so I thought of a different solution: I decided to fix the board to a support glued to the neck block, and install/remove it through the battery box, located nearby:

You can see that I had to cut the two “horns” from the control board, but fortunately that could be done because there were no conductive traces on them. This is the guitar before gluing the top:

Of course, I practiced the installation from outside before closing the sound box. I saw that it was rather simple. The screw that secures the board to its support was easily accessible through the hole for the battery:

I checked also that the preamp could be inserted through the battery hole. Archtops have such poor access inside them that checking these things is absolutely essential.

Regarding the bridge, as this time it was not going to be very low I decided to use the usual archtop thumbwheels. I had to separate them more to make room for the pickup and avoid contact between the thumbwheel and the output wire:

Consequently the saddle was also a little longer, but it was also sturdier, so I made it from ebony:

The saddle insert was similar to the one that I used for my first FMI-equipped guitar above. It had small notches cut in the face that contacted the piezo to increase the pressure under each string (sorry for the confusion: the saddle in an archtop guitar is that big ebony piece. There is an additional piece on it,

which here I have called saddle insert, and is quite unusual in archtop bridges. It looks a lot like the saddle in a flat top guitar bridge.)

The underside of the bridge has a cavity that allows limited movement of the bridge to correct the intonation:

Installing the bridge was easy. Before drilling the hole for the wire, I marked the position of the bridge with masking tape, taking into account the usual compensation:

I secured it until everything was in place:

I installed the preamp at the tail. The FMI comes with a chrome strap holder attachment (still not installed), but I need it gold. I wish Fishman included a gold one in the kit, as most guitars beyond certain price have gold hardware.

Finally, I put everything together:

All this took some time to set up, but it is a pleasure when you see that everything falls in place as you expected. And the finished instrument is a joy to hear and to look at: