04 October 2014

Installing a Pickup and Preamp in a Yamaha FG700S Acoustic

Fig. 1. Yamaha FG700S
If this post isn't all that informative, that's at least partly because I didn't take that many photos. I was so intent on not destroying the guitar that it didn't even occur to me to take photos until after I successfully cut the first hole. But first things first.

I have an inexpensive Yamaha FG700S, which is a $200 guitar new, but I got mine used for $140. For a solid top guitar, it's hard to beat for the price, and I like this one a lot. However, shortly after buying it, I wished I had bought an acoustic electric. I put it on craigslist so I could upgrade to an acoustic electric, but got no bites. So I bought a $13 piezo pickup, and a $22 preamp and input on ebay. I didn't want to spend too much, because I felt there was a decent chance that I would destroy the guitar while trying to install the pickup, since I had never done this before. And I figured if I liked it, I could always upgrade to a better preamp and pickup.

The part I feared most, obviously, was cutting two holes in the guitar. Measuring and cutting a hole in a flat plane is easy, but the preamp goes on a curved section of the guitar. I measured the preamp housing several times, placed it along the edge of the curve in the guitar body to see where it would fit best. After finding a sweet spot, I used a razor blade to make little nicks in the finish marking the border of the section to be cut out. I then marked the border with masking tape (Fig. 2).

I drilled the corners with a 1/2" bit. I started to use a jigsaw to cut the hole, but the wood was too fragile. It made a sloppy cut. I tried a utility knife to score the border of the hole, and I kept scoring until it poked through. This didn't take as long as expected, and the cuts were pretty clean. I sanded the hole and inserted the preamp. It was a little tight here and there so I sanded it again and it fit. I didn't get photos of the preamp installation, so here is the during and after shots of the input and the after shot of the preamp:

Fig. 2. Cutting the hole for the input. Installed input and preamp.
I did the same exact thing with the input. Then I plugged the piezo pickup into the preamp and stuck it under the bridge.
Fig. 3. About to place the pickup under the bridge.

I should note that the preamp came with as under-the-saddle pickup (Fig. 4). I preferred the kind that mounts inside the guitar under the bridge (Fig. 3, above), so I snipped the input off the former and and soldered it to the latter and used that.

Fig. 4. Cheap under-the-saddle pickup

Everything's in, and although I made the input hole a hair too big (so there's not enough wood in one corner for the screw to grab), it went better than I expected.