How to Install a Fender Blues Junior Bias Trimpot Without Drilling Holes in the Board

Where Fender Blues Junior mods are concerned, Bill M of billmaudio.com is truly a player on the world stage (see my previous appreciation of him and his mods here). The info and kits he provides on his site have been invaluable to me and countless others from around the world. So it is only with due respect (and sometimes awe) that I disagree with him on one issue: the need to drill holes in the board to mount a trimpot for bias adjustment.

His point is that bent leads on a trimpot may cause the pot to be wobbly, which in turn can cause the leads to break. First, the trimmer I used is not wobbly even with bent leads. Second, if you can use hot glue to secure other components on the board (electrolytic caps, multi-wire cables), you can use it here if you want. Again, there is no need to with the pot I used (but see my final note in the last paragraph). This is not the same pot that is included in Bill M kit (same specs, narrower housing), so I have included a close-up shot of it so you can find it. I got mine on eBay—a Bourns 3296 variable resistor, 50K ohm, 25-turn (Fig. 1).

 

Fig. 1. Here is the trimpot I installed in my Blues Junior. It is a little narrower than the one provided in Bill M's kits.

I recently installed this trimpot in my Blues Junior III (details vary among different BJr versions—check billmaudio.com for details). To avoid drilling a hole in the board (which I have done once before, and very nearly botched it), I bent the middle lead of the pot straight out and spliced a piece of wire to it (Fig. 2). I bent the outer leads slightly inward and down (note: you really only need to bend one lead, but I have an often unnecessary habit of centering things). I pressed the pot to the board and soldered it in place (Fig. 3).

Fig. 2. Ready to install: trimpot with extra wire spliced onto the middle lead and outer leads bent slightly inward

Fig. 3. Installed trimpot.

Because this trimpot housing has little nubs/standoffs on the edges (visible in my beautifully rendered and incredibly realistic diagram in Fig. 4 below), there is space underneath for the lead to fit between the housing and the board. As a result, when the trimpot is mounted, it is snug, not at all wobbly, and perhaps most important, reversible. Further, it was easy and not even remotely nerve-wracking.

Fig. 4. This is what a diagram looks like when it is created in Word and Paint. But you get the idea.

As a final note, though—and I can't stress this enough—I would personally take Blues Junior advice from Bill M before I took it from me. I am only sharing this as an alternative for people who aren't willing to drill a hole in the board. If that's a dealbreaker, this alternative might work for you.

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.