Sunday, February 28, 2010

1982 Gibson Chet Atkins CE, part 3

"Resistance is futile"

The Borg of Star Trek were wrong, resistance is not futile, at least when it comes to fixing the pre-amp in this guitar.

Problem: the G string is much louder than the other strings.

Solution: more resistance.

The pickup has separate piezo transducers for each string, with six trim pots on the pre-amp board to adjust volume balance from string to string. Unfortunately, this doesn't work as advertised, and appears to be (as some guitar forum posts would suggest) a common problem with this model. The output of the G string with its trim pot turned all the way down is louder than any other string turned up to max.

I managed to locate a schematic of the pre-amp circuit board (saving me the hassle of tracing it out by hand). The area of interest is the mixing stage where the trim pots are located...

 

Each transducer is connected to a 5 M trim pot in series with a 4.7 M fixed resistor, an adjustment range of 4.7 to 9.7 megohms. That's not sufficient for my honking G string, but another resistor in series should tame it. Since the trim pot is 5 M, I need to add at least 5 M to shift the adjustment range to something useable. Luckily, I had a 5.1 M resistor in my parts drawer.

 

The 7-wires from the pickup (one for each string plus ground) are soldered to pins on the pre-amp circuit board. I unsoldered the G-string wire (3rd pin from the right) and soldered the resistor in its place, reconnected the wire to the other end of the resistor, put on some new strings, tuned it up, plugged it in, and easily adjusted the G-string output to balance the others. So simple, I can't believe I didn't try this fix years ago!

The amplified tone is remarkably better than before, but I can't say for sure if it's the new ebony saddle shim, or just the fresh set of strings. It will take a couple of days for the nylon strings to stretch enough so I can record some audio clips for reference. That will help in evaluating whether there's a significant improvement when I try the traditional bone saddle with a modern transducer.

Saturday, February 27, 2010

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.

Friday, February 26, 2010

1982 Gibson Chet Atkins CE, part 1

"She's got a body to die for, but..."

This is my '82 Gibson Chet Atkins CE, Custom Shop Edition:


In 1981 the legendary Chet Atkins came to Gibson with a prototype for a solid-body nylon-string acoustic electric guitar, something he could play on stage at high volume without feedback and still get a nice acoustic tone. The resulting CE (classical electric) model was produced by Gibson for over 20 years and widely adopted by such notable players as Willie Nelson and Earl Klugh. It's become quite collectible since Chet's death in 2001.

I acquired this guitar about 20 years ago from my good friend and fingerstyle virtuoso Danny Heines, www.dannyheines.com. At the time it seemed to be a natural choice for my jazzy-bluesy fingerstyle repertoire in an amplified band setting. And with such stellar endorsements as Earl Klugh and Chet himself, this should be one fabulous guitar... right?

Well... not exactly! Although it looked and played great, I never could really warm up to the dull quacky plastic tone of the pickup (which is pretty much all you hear when amplified) and no amount of EQ could rescue it, at least to my ears - plus it was impossible to get the volume properly balanced from string-to-string. As a result, this guitar has mostly languished in its case - only occasionally taking it out, playing a little, and promising to someday figure out how to make it sound as good as it looked and played.

As the first project in my Ten Guitars odyssey, I decided to finally make good on that promise.


Most serious fingerpickers (myself included) would credit Chet Atkins as the biggest single influence in the art of contemporary fingerstyle guitar. I've learned a lot from Chet over the years while attempting to steal a few of his licks and techniques, I figure the least I could do in return would be to put some serious T.L.C. into one of his namesake signature guitars.

"Years from now, after I'm gone, someone will listen to what I've done and know I was here. They may not know or care who I was, but they'll hear my guitars speaking for me."
– Chet Atkins, CGP

1959 Rickenbacker 450 Combo, part 1

"The Accidental Guitarist"

My first serious encounter with the guitar was accidental, or more precisely, the result of an accident. I broke my left arm playing football as a teenager in 1959. The compound fracture was so bad they had to put it back together with a metal plate and screws. When they removed the cast three months later, my elbow was so stiff I couldn't straighten it, and there was no strength in my hand or fingers.

I was at a friend's house a few days later, showing off my surgery scar, when his father (a guitar player) suggested guitar therapy for the lame arm. He picked up his beat-up old Stella steel-string flattop, showed me how to tune it, strum it, a few easy chords, and told me to take it home for awhile.


As soon a I put my hands on the guitar I was hooked! I completely forgot about the injury, all I cared about were the cool sounds I could make. Within a week I'd figured out the beginning riffs to "Guitar Boogie Shuffle" and "Rebel Rouser" by ear and my left hand was getting stronger every day. By the time my next birthday came around, I'd convinced my parents to get me an electric guitar, a brand new Rickenbacker 450 Combo model solidbody with two pickups and a sexy red Fireglo finish, very cool!


It was a great time to be a teenager with an electric guitar - Rock'n'Roll was in it's prime and the radio was filled with guitar hits by Chuck Berry, Duane Eddy, the Ventures, any many others. I learned them all, wearing out the grooves in my 45rpm records by dropping the needle in the same spot over and over and over trying to figure out how to play a particular lick. I couldn't afford an amplifier, so I built one from scavenged parts and tubes from old radios. I put together a band called "The Road Runners" with a couple of guys from my high school to play the annual talent show, we brought the house down! A few months later I was hired by a real band that played wedding receptions and local night clubs, nice gig for a teenager... You mean I actually get paid cash to have this much fun?

Now, after all these years, the 6 inch scar on my left arm still marks the spot where there's hardware screwed into the bone underneath, but it also marks the beginning of an extraordinary lifelong musical odyssey that took me all over the world. Wherever I travelled, my guitar was my "all access" pass, my interpreter when there was no common language, my magic key to unlock doors to otherwise inaccessible places, sometimes following and sometimes pointing the way. A borrowed Stella restored my left arm, but my Rickenbacker gave me the whole world, asking only for an occasional set of new strings in return. What a bargain! It was my main gig axe until I bought a Gibson ES-345 in 1971. The Gibson was sold a few years later, but the Rick is still around, here's what it looks like today...


By the mid-1970s, the original red Fireglo was so beat-up that I stripped it down and did a natural finish, replacing the brass plated metal pickguard with a custom made black plastic version. At the same time I installed a set of Schaller sealed tuners, a brass nut, a Gibson SG style bridge, swapped the bridge pickup with a 1962 Telecaster pickup, rewired for single volume and tone controls, and refretted with jumbo frets. Vintage purists might not approve of my mods, but it was a much better guitar afterward.

Although still playable, it's 50 years old and needs some serious work. The truss rod is bent at the nut (on the verge of breaking) and the fretboard has started to delaminate from the neck. At this time, I haven't decided whether to do a complete restoration to its original 1959 vintage Fireglo glory, or simply make the necessary structural repairs. Until I do, there are other guitars ready to be turned into sawdust!

Old Love, New Life

The relationship between guitarist and guitar is an intimate and passionate love affair, unlike any other, so it's naturally difficult to let go of an old instrument when a new one comes along. A new guitar is exciting and alluring, promising intriguing new sounds and possibilities, while the old is a faithful companion with a priceless sentimental history. As a result, many of the guitars I've acquired during the past 50 years remain in my possession, and some would qualify as vintage collectible. There are two or three that I play quite often, but the others remain in their cases for years at a time, sadly neglected, rarely played, still bearing the scars of too many gigs on the road.

About a year ago I was pondering what to do with them, perhaps at least count them as I wasn't even certain how many I had. I opened the dusty cases, played a little, and surveyed what needed to be fixed. For some, a new set of strings, fret dressing, set-up, and other minor detailing might be enough. Others, however, needed more ambitious repairs like bridge replacement, refretting, cracks fixed, etc. There were ten guitars in all, including three bass guitars and a beautiful Hawaiian lap steel from the 1930s, plus a nice Turkish Oud that I bought in Istanbul a few years ago. Every one is a fine instrument that deserves to be played, not exiled in storage for sentimental reasons!

With that in mind, I resolved to overhaul the entire collection - focusing primarily on playability and tone, and then aesthetics - to give these old loves new life so I'd be enticed to pick them up and play more often. The luthiery aspect of this project is daunting in itself, but the promise to play them afterward could prove to be even more challenging, especially with the Oud and Hawaiian lap steel which I'll first have to learn how to play. And there's always the risk I might get one fixed up really nice and play it obsessively, letting the rest of the project lapse into limbo.

Hopefully, recording my progress in this blog will help me stay on track and maintain a balanced perspective between the task at hand and my longer range goals. I gratefully thank the many guitarists, luthiers, and woodworkers who have taken the time to share their invaluable knowledge and experience online. In return, I offer this public journal of my endeavor so others might benefit as I have... welcoming feedback, questions, tips, or advice.