1982 Gibson Chet Atkins CE, part 2

"A bridge over troubled water"

Main goal: Make this guitar sound as good as it looks and plays!

Also to-do: Craft a new bone nut, level and polish the frets, repair stripped screw holes, and possibly refinish the neck.

Actually, the acoustic tone is already pretty sweet unplugged, although rather quiet as you might expect from a solid-body guitar. It has an acoustically chambered mahogany body with a solid spruce top (which should be a fine recipe for guitar tone) and if you put your ear right up against the wood and play a few notes, the sound is very rich and detailed with tons of sustain from the lower strings. So the tone is already in there, it just somehow needs to be captured and sent off to the output jack. This shouldn't be terribly difficult given the latest generation of under-saddle transducers.

OK, time to strip off the strings and take a peek under the hood...

The bridge saddle pickup is a massive 10mm wide hunk of plastic set in an anodized aluminum u-channel that wraps around the sides and bottom. Underneath all that plastic are 6 piezo transducers (one for each string) with a 7-wire cable to an onboard pre-amp. The slot is about 0.5mm too wide for the pickup which explains the tiny pieces of guitar picks to shim the saddle snug in the slot. Under the saddle is a tapered bakelite shim sanded down to get the proper string height - and of course if you sand too much there's always the foil wrap fix - ugh!

From an acoustic tone perspective, everything about the design of this bridge saddle is wrong! It appears to be an attempt to isolate the transducers from the guitar body and pick up only string vibrations. However, a vibrating string by itself doesn't have much musical tone, especially a nylon string. In a guitar, string vibration is transmitted through the bridge saddle to the soundboard which responds by vibrating according to its own complex resonance modes (accentuating some overtones and attenuating others), and this soundboard vibration is transmitted back through the saddle to the strings, etc.

The back and forth dance between strings and soundboard defines the characteristic tone of the instrument, and the key player is the bridge saddle. Ideally it should have excellent acoustic properties, minimum mass, and be squarely mated to the bottom of the bridge saddle slot along it's entire length to insure a balanced sound energy transfer from all 6 strings. A well crafted traditional bone saddle has all of these qualities. The CE saddle above has none! And a closer inspection of the saddle slot reveals some more surprises...

 

Now that's one ugly saddle slot!! The bottom is rough and uneven (as if hastily routed with a dull bit) and the entire slot is painted with a thick layer of black conductive shielding paint (another tone damper). The treble end of the slot has a hole for the pickup cable and a piece of copper foil (under the black paint) that runs about 12mm along the slot bottom and down into the hole where it's soldered to a ground wire. With all that crap in the slot there's no way to squarely mate the saddle to the bottom, it's no wonder they had to build the pickup in a sturdy aluminum frame. And since the u-channel is grounded through the pickup cable, there's really no need for all that shielding paint in the slot.

So with the serious problems identified, it's time to consider my options...

1. The simplest fix is to rout the slot down perfectly flat (which will also get rid of the thick paint layer), craft a new hardwood bottom shim to get the proper string height and insure the saddle is squarely seated, and reuse the original pickup. I'm certain that this will improve the tone considerably although probably not enough to offset the tone-sucking dampening of all that plastic and aluminum between the strings and guitar top.

2. A more ambitious and expensive fix is to rout the slot flat, shape a piece of rosewood as a close fitting plug to fill the old slot, rout a new slot for a traditional 1/8" bone saddle, and install a modern under-saddle transducer with a matching pre-amp.

I plan to experiment with both. The first option is quite easy but I'm really curious to hear if a state-of-the-art transducer can capture more of the sweet body tone. In any case, I first need to put the saddle back in the slot along with the old funky shims, get out the digital caliper, and take accurate measurements of the saddle height at both ends.

Once the old saddle is disconnected and out of the way, I'm ready to set up the routing jig and start making sawdust...

I remove just enough wood to get the slot bottom perfectly flat and level. Yep, there's rosewood under all that black paint. When the routing is finished I put the saddle back in (without any shims) and measure the saddle height at both ends again. Comparing with my previous measurements will tell me the exact thickness and taper required for a new bottom shim.

Here's the new ebony shim, perfectly shaped to fit the slot and tapered to provide the correct saddle height at each end. I put some thin strips of aluminum tape on the sides of the saddle so it fits snugly in the slot...

Before I put on new strings, I'll level the frets, repair the stripped screw holes in the headstock for the tuners, and I still need to do something about the string volume balance on the pre-amp.