SB-2 Shielding

There really aren't any pictures of the cavity shielding being done, but it's a straightforward task that really is self-explanatory.  The main thing to get across with this pictorial are the details and tricks to aid in the overall job.

If soldering isn't your thing but you'd like to learn, click here for the basics.

Click the images for a larger version.

This poor old bass found its way to our house a few years ago looking for fresh strings, a setup, and some TLC.  It's a 1999 SB-2 that's been in the hands of high-schoolers.  It has a few rough spots, but it's a sound player.

I decided to turn this into a small project.

Here's what the original electronics looked like.  This is G&L standard.

This image shows the shielded pickup cavities and the channel that runs from the neck cavity to the control cavity.  There's lots of room around the neck pickup because it has the pickguard.  However, clearance around the bridge pickup is tight.  The sides aren't too bad, but the ends are very close.  I shielded the bottom and long sides of the cavity and ended up with a movable pickup.  If you look carefully, you'll note that there is a small piece of foil covering the hole to the control cavity.  More on that in a below.

Those nice neat holes in the foil for the springs were made with this and a small hammer. A couple medium-sized blows to the punch and the foil was scored enough to easily lift out.  The body was well supported for this process.

Additional shielding on the pickguard.  Shielding the entire back of the guard is overkill.  The pickup cavities and lead channels were covered.

This image shows a wire soldered to the bottom of the control cavity. This wire, when connected to the star ground lug shown and described below, ties all the foil on the bass to ground.

The completed control circuit - sorta. The bundle of green wires is comprised of all the various ground connections from the entire instrument soldered to a 3/8" ring terminal, which is clamped in place under the neck pickup control. This is the star ground I mentioned above.  Care should be taken when orienting the jack so that it doesn't short to the foil on the side of the control cavity.

I said that the circuit was "sorta" complete because this image shows the pots wired backward. The red and green pot leads should be swapped. This was corrected before the bass was buttoned up.

Under the heading, "It's All In The Details", I also shield the hole that runs between the bridge pickup cavity and the control cavity. You can see one end of this shield here.  Note that this shield will tend to slightly darken the sound of the pickup whose leads go through it.  This would be the case if the wires themselves were shielded.

The shield tube is made using a piece of RG59-U coaxial cable - TV cable.  It has to be the good stuff with copper braid shielding.  I strip the braid out of the jacketing to get the tube.  What you see below are, left to right, the piece of coax, the empty outer jacket, the inner conductor with dilectric, and an empty copper braid tube.

I narrow one end and tin it to hold it together, then feed it through the hole in the body.  I then spread the other end into a bell shape and solder it to a cavity wall.  I cut the excess off the now free end, leaving about 1/4" protruding into the cavity.  I spread it into a bell shape and solder it to the other cavity wall. This is where that little piece of foil in the bridge pickup cavity gets used - as a solder point.  Care must be taken in the bridge pickup cavity to keep the end pushed as tightly as possible to the wall when soldering to avoid interfering with the pickup cover. Push the wires through as seen above and install the pickup.

Copyright 2009 Ken Baker and