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Gibson Chet Atkins electronics upgrade


marpar

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I think I mentioned that I had some problems with the preamp in my Chet Atkins guitar. Most probably they resulted from the age of the guitar. I still intend to fix it but in the meantime I decided to make a new version of the preamp. The new version is a drop-in replacement for the old preamp (the same size, the same mounting holes, the same connections) but it is more modern. It uses SMD components and modern parts like, e.g. J201 audio JFETs. See attached photo. I works great - all the problems I had with the previous preamp are gone.

I still have some other ideas to improve the sound of the guitar. The first on the list is shielding of the cavity with copper tape. Another is a complete new version of the preamp. It's because the Gibson preamp uses some outdated circuits (like "grounded gate mixer", which was mostly used in RF circuits).

Stay tuned if you want to see it.

 

Marco

post-91046-047170800 1540636550_thumb.jpg

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The original version of the preamp was checked with LTspice simulation program. Some components needed to be adjusted in order to improve the frequency response of the circuit (and my version is already adjusted).

After a short discussion of the circuit on the LTspice discussion group it was suggested to build a much more modern version of the preamp (and hopefully better). It uses so called "charge amp" circuits - there is one for each string separately. The new version of the preamp was also tested first with LTspice and then build - see attached photo. As you can see this is also a drop-in replacement for the original preamp. It is quite complex; it uses SMD components (0603 packages) and is double-sided (the charge amps for each string are on the bottom layer of the PC board).

Now I have to play it and see which version is better. It seems that the latest version is the best and will stay with me and my guitar [rolleyes]. If anyone needs such a preamp, I have 1 spare board that I can share.

 

Marco

post-91046-059125400 1541063563_thumb.jpg

Edited by marpar
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  • 2 years later...

Hello Marco,  Nice project and upgrade. I searched for schematics or repair and found this post so hope you can help.

I have a Gibson Chet Atkins CEC 1993 model with a non working preamp, any way to get schematics  for original board (EXP 1213 Rev. 1.0 Board) or a new board BOM that you built?

Thanks in advance,

Tony A

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  • 6 months later...

Please find attached schematic of the preamp with

expected voltages. They may differ by 10% from the actual circuit. I

assumed that the battery voltage is 9V (a new battery sometimes has

9.6V). The first test would be to measure the voltage on the D1 diode.

It should be the same as the battery voltage but in case there is

something wrong with the wiring, it will be different. Please measure

the voltages from the bottom of the PC board in order to avoid making

a short circuit. You have to identify the transistors (there are only

4 of them), find out their pinout (using datasheets) and verify the

voltages one by one. If any one is different, make a note and let me

know about it.

Please check that the wires at the pots are not broken.

Edited by marpar
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On 11/1/2018 at 5:23 PM, marpar said:

The original version of the preamp was checked with LTspice simulation program. Some components needed to be adjusted in order to improve the frequency response of the circuit (and my version is already adjusted).

After a short discussion of the circuit on the LTspice discussion group it was suggested to build a much more modern version of the preamp (and hopefully better). It uses so called "charge amp" circuits - there is one for each string separately. The new version of the preamp was also tested first with LTspice and then build - see attached photo. As you can see this is also a drop-in replacement for the original preamp. It is quite complex; it uses SMD components (0603 packages) and is double-sided (the charge amps for each string are on the bottom layer of the PC board).

Now I have to play it and see which version is better. It seems that the latest version is the best and will stay with me and my guitar [rolleyes]. If anyone needs such a preamp, I have 1 spare board that I can share.

 

Marco

post-91046-059125400 1541063563_thumb.jpg

The low noise (HUM......) on my Atkens is annoying. I hope your updated version solves this problem. Where can I buy it?

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  • 1 month later...

Good day.  I am extremely interested in your version of the pre-amp for a  Gibson CE. I have a very early version of the guitar with a tremendous feel to it. However the electronics are shot. I managed to source a new bridge as the original eventually had volume drop out for a few of the strings. But the guitar has also clearly got problems with the preamp as well. I am based in the UK and would like to discuss this further if you are amenable.

Terence

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Hi, sorry for my bad English, I don't sell parts, I just made mine out of passion. I can help anyone who wants to make one but has to build it at home. What you have to use depends on whether you want to have six piezos (as in the case of my Gibson Chet Atkins CEC with nylon strings) one for each string or not (on the market there are few pick-ups with six separate piezos) if I remember correctly the SST electronics didn't have a preamp with six separate controls and therefore also the pick-up I think was with a single piezo.

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  • 3 weeks later...
On 10/27/2018 at 12:49 PM, marpar said:

I think I mentioned that I had some problems with the preamp in my Chet Atkins guitar. Most probably they resulted from the age of the guitar. I still intend to fix it but in the meantime I decided to make a new version of the preamp. The new version is a drop-in replacement for the old preamp (the same size, the same mounting holes, the same connections) but it is more modern. It uses SMD components and modern parts like, e.g. J201 audio JFETs. See attached photo. I works great - all the problems I had with the previous preamp are gone.

I still have some other ideas to improve the sound of the guitar. The first on the list is shielding of the cavity with copper tape. Another is a complete new version of the preamp. It's because the Gibson preamp uses some outdated circuits (like "grounded gate mixer", which was mostly used in RF circuits).

Stay tuned if you want to see it.

 

Marco

post-91046-047170800 1540636550_thumb.jpg

 

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On 10/27/2018 at 12:49 PM, marpar said:

I think I mentioned that I had some problems with the preamp in my Chet Atkins guitar. Most probably they resulted from the age of the guitar. I still intend to fix it but in the meantime I decided to make a new version of the preamp. The new version is a drop-in replacement for the old preamp (the same size, the same mounting holes, the same connections) but it is more modern. It uses SMD components and modern parts like, e.g. J201 audio JFETs. See attached photo. I works great - all the problems I had with the previous preamp are gone.

I still have some other ideas to improve the sound of the guitar. The first on the list is shielding of the cavity with copper tape. Another is a complete new version of the preamp. It's because the Gibson preamp uses some outdated circuits (like "grounded gate mixer", which was mostly used in RF circuits).

Stay tuned if you want to see it.

 

Marco

post-91046-047170800 1540636550_thumb.jpg

Hello Marco. Is your preamp for the Gibson Chet Atkins for Sale?

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