Gibson Chet Atkins CE 1986 that hums!

[Scott Wackerman]

Hi,

 

I've checked all the solder connections and they are fine. It seems the pre-amp is compromised. The owner wants to keep the original volume and tone switch in the rotational orientation as from the factory. So far, most that I've spoken with resolve to change out the pre-amp, volume and tone parts. The problem is; the switches will not be in the same rotational orientation with the after market parts.

Any help would be most appreciated. If you are unclear about my problem then please review the photo's or get back to me.

 

Gibson_ChetAtkins_CE_1986_%20008.jpg

 

Gibson_ChetAtkins_CE_1986_%20013.jpg

 

Lastly, when I contacted Gibson, their solution would change out the original configuration! Arrrgh!

 

Regards, Scott 

 

[Tom Krebs]

I did a search and found the schematic and photos:

 

http://guitarsawdust.blogspot.com/2010/02/1982-gibson-chet-atkins-ce-part-3.html

 

[Scott Wackerman]

Tom,

Thanks for the link. I made a little comparison photo of what I have an what is on that guitarsawdust page and thought there are similarities - The board in the guitar I have (right side) has a lot less components.

Every little bit helps!

Regards, Scott

[Mac Walker]

So the pickup in this guitar is not the original hex pickup, it is an aftermarket humbucker?  It's clear where the other five trim pots were cut off of this board at some point, the remaining leads are clearly visible.  If it were factory original you would not see these leads.

 

I am wondering if the preamp is OK, and you just have a weak pickup, with poor signal to noise ratio (hum) as a result?

 

What is the coil resistance of the (non-original) humbucker?

[Scott Wackerman]

Hi Mac, This is a piezo pickup on a Gibson solid body classical (nylon string guitar). Resistance measures 3.5 ohms. However, the signal to noise ration brings about a question of compatibility. Rolling the volume off reduces the noise significantly. Obviously, a person spent time modifying this guitar.

We may be on to something here!

Again, for clarification, this is a piezo pickup.

 

Regards, Scott

[Rob Mercure]

Hey Scott,

 

Rob here and just wanted to note that I'm glad that advice you got here helped with your problem.  I would have replied sooner but  my health took a dive for the worst and I'm just now getting back on my feet.  The electronics part of guitar repair in general is honestly pretty simple and only gets complicated if you wish to modify response of controls and pickups and such and then have to really master the difference between impedance and resistance - for repairs just being familiar and practiced with Ohm's law is sufficient as well as being able to solder and use other hand tools.  It does get tricky when you start to get into preamps and on board EQ but honestly as a musician and not in any way the tech side of me I've only felt that they added a tiny, tiny bit of utility to my playing and musicians have gotten "spoiled" - as have the rest of the population - with too many consumer choices (I grew up in a neighborhood with a "party" telephone line shared between six neighbors - those kids with their ears constantly to the phone should try dating when a neighbor can pick up the phone and listen in). Unfortunately "Murphy" rules the universe (second law of thermodynamics) and one just have to realize the the more and more complicated your "stuff" the less realiable the whole lot is and the greater need for frequent preventive maintanence.

 

Luck with it from here.

 

Rob

[Paul Verticchio]

Hi Rob.

 

Sorry to hear about your health issues.  You have my personal wish for a complete and quick recovery.

 

It's good to see you back on the site (:

Paul

[Rob Mercure]

Thanks, I hope your wishes help.  But I should know this month whether I'm facing the prospect of a liver transplant which puts my long term physical access in question.  I've been getting together a "plan B" just in case and attempting to find promising younger tool and good "junk" (unrealized materials) users who would use my insane collection if I wind up having to take harp lessons <grin>.  Since most of my material is electronics - tube oriented; then wood working - instrument oriented;  and then tools of all sorts it's been hard to find and meet folks who I feel would use my legacy.  I hate "collectors" and really don't want good tools to wind up hanging on a wall nor do I want much of my collection to wind up in a dumpster just because whoever has to deal with it doesn't know what it is or what potential use it has.  Even of the close friends who've agreed to be co-executors none has all the interest I have so I'm cobbling up a mix that includes one of each and still have a few gaps.  And even if I don't have to use plan B I've realized that I still have too many potential projects worth of materials to reasonably deal within the next 20 years at my best energy levels (based on my age and how long my grandparents lived) so I still have to distribute probably at least 1/2 of so of my "stuff."  And it would really make housecleaning and organization easier as I've never had sufficient work space for interest that should really have at least 4 work bench areas (the mechanics and sawdust woodworking separate also).  Being a generalist is such a blessing and curse at the same time! 

Hopefully though I'll be kicking for a while as I'd really been looking forward to a new end career as a "grumpy old fart."

 

Rob

[Scott Wackerman]

Hi Rob, 

 

I look forward to more of your helpful and informative posts as you will recover and feel better soon.

All the best to you and your family! Scott

[John Gummere]

Re:  Intermittent and low signal (or hum) problems with Gibson CE/CEC hex pickups.  Mine is CEC serial no. K005, and it had frequent dropouts on the low E string piezo transducer.

I found that if I gently wiggled the wiring in the pre-amp cavity while the instrument was 'live', I got a better idea of where the bad connection problem was...several places, it seemed.  So at first, I decided to re-solder the joints where the pickup was connected (with that delicate printed circuit ribbon cable) to the amp board .  I used a low wattage iron w/ pencil tip, but the cable immediately delaminated before I could wick any of the old solder off, which made me realize that it was toast, so I clipped the cable (and the old guitar strings) and removed the pickup entirely.

I hoped maybe, just maybe, that the pickup might be somehow repairable.  The ribbon cable had also deteriorated where it entered the pickup body, so I pried it all apart (the saddles were lightly set in silicone glue) and discovered not only could it not be repaired, but also that its design/construction was rather poorly done.  The piezo 'bricks' are dovetailed into their discrete nylon saddles and have a common bare ground wire along the top (relieved with a common groove under the saddles).  The wire is solder-tacked to each brick, and when I disassembled the pickup, some of those solder joints practically fell off.  I've heard that in a good solder joint with thin gauge wire, one should be able to snap the connecting wire off before the solder itself breaks.  Apparently the builders were relying on the (small) metallic content of the bricks to adhere to the solder, but maybe corrosion etc. set in and weakened them.  Whatever, the guitar now lies in its case, naked of strings and pickup.  I really like this instrument with its long sustain...what to do, what to do.

I had an interesting phone talk last Saturday with Kirk Sand (of Kirk Sand Guitars in L.A.), one of the co-designers and builders of the original Gibson CE/CEC model.  He confirmed that, yes, the ribbon cable was soon abandoned, and the subsequent six-wire cable they replaced it with had problems, too.  It's just an inherently delicate and tight arrangement, it seems.  He said I 'might' be able to find an original replacement hex pickup, but don't get your hopes up.  The first ones were made by Gibson, which then subcontracted their manufacture to Shadow, a German pickup maker.  They've been discontinued for years.

The workaround seems to be to replace the hex arrangement with a single piezo unit (Shadow still makes one in the same 8mm x 80mm form factor), and try to shape the sound using some sort of graphic eq and/or efx downstream from the pre-amp.  Kirk said it might work, but probably not as well as the separate trimpot volume controls.  Oh well...[sigh].  Nice idea, the hex was.  Worth a try at resurrecting somehow, though.  Maybe further research could locate a sturdier hex design, but I bet it would be an expensive one, if any. (unless I can figure out a way to attach that ground wire to the piezos more securely).

[Scott Wackerman]

Hi John, 

The guitar can be resurrected with new internal components and switches. There are various piezo pickup and pre-amps available. I had tough constraints regarding the guitar I was working on it was customer owned and not mine (this would end different if it was mine and it would be working today). He wanted it fixed - I could accomplish that but he wanted to maintain all the original parts - That I couldn't manage. I tried all the above. Add this complication, the owner/player plays a style similar to flamenco where he slaps the guitar. The material between the electronic cavity and the guitar surface is about 1/8th of an inch - Once I got the guitar to be quiet, he'd play the guitar as he is used to playing (slapping the surface) and invariably the phantom noise would return or signal would drop. I tried purchasing new parts from Gibson but as you know - the project is discontinued. Thanks Gibson!

This was frustrating project. I completed calls, investigated all info available on-line, measuring, and attempting to design my own pre-amp to buying a pre-amp off the shelve.  However, all my effort was denied due to stock part incompatibility.  Finally, I found myself back where I started back and net zero. Your last paragraph contains the answer. Grounding shouldn't be an issue or at least for the unit I worked on. I was looking at replacing the parts and having a machine shop make some plates to I could attach pots that are perpendicular to the guitar as opposed to those thumb-wheels that came with the guitar. Using a down stream pre-amp would work but is not handy or elegant. Alas, tis not my guitar and the owner didn't want that so I guess this guitar also sits in a case somewhere without a smile or strings.

If the guitar was mine I would have retro-fitted the pot plates, installed a robust new piezo and pre-amp and move along. This is not the cheapest method. In addition, the guitar would now be modified. However, this design was myopic at best at the time of release. With the poor design I doubt this will ever fetch much in the vintage market. Current models or like models all have systems like I would use but they use unknown vendors where once again - someone else will be faced with a similar conundrum. Cheers! Scott

 

[John Gummere]

Thanks Scott, would love to hear more about your adventures looking for improved components and machining.  Actually, I think the original pc board and its op-amp seems adequate enough, though it could use more overall shielding attention, coaxial signal cables etc.  When I first looked in there, I could see it was an early production "cut corners" job (the pc board itself actually had a corner crudely sawed off, so it would fit into the amp cavity!).

I'd say let's forget about the Gibson company and their abandonment of this beautiful child...it's now up to us independent tech-heads to get it up and walking again.

Flamenco, eh?  Nice sound, that.  I myself am into Brazilian music, Baden Powell's fast sambas in particular.  I've learned to play a few of his tunes, and I will say that playing them on this instrument (when it was working right, with a little soft chorus and reverb added) sounded like a golden nightingale.

What if there were small metal plates on top of those piezos, and the ground wire was simply pressed down by string pressure to make contact?  Maybe one would have to take it apart once in a while to clean it, but the resulting sound might be worth the trouble.  Whatever. 

Interesting footnote:  A friend of mine who had one of these guitars (he was the one who turned me onto them) was annoyed by forgetting to pull out the plug, and the battery would die.  He installed a mercury position switch on the positive battery wire, so that when he put it up on the guitar stand it would automatically shut itself off.

[scott gannon]

Interesting  post. I don,t do much instrument work, but the most difficult thing I have dealt with so far is the diplomacy of telling a customer that their style is effecting things also. Vexing to say the least. Good luck Buddy!