marpar Posted October 27, 2018 Share Posted October 27, 2018 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 It's because the Gibson preamp uses some outdated circuits (like "grounded gate mixer", which was mostly used in RF circuits).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 Quote Link to comment Share on other sites More sharing options...
marpar Posted October 27, 2018 Author Share Posted October 27, 2018 I started shielding the cavity. It looks like this: Quote Link to comment Share on other sites More sharing options...
marpar Posted November 1, 2018 Author Share Posted November 1, 2018 (edited) 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 . If anyone needs such a preamp, I have 1 spare board that I can share. Marco Edited November 1, 2018 by marpar Quote Link to comment Share on other sites More sharing options...
Tony A Posted November 14, 2020 Share Posted November 14, 2020 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 Quote Link to comment Share on other sites More sharing options...
marpar Posted May 15, 2021 Author Share Posted May 15, 2021 Hi Tomy, sorry for the delay. https://funkyimg.com/view/3c3VY Quote Link to comment Share on other sites More sharing options...
marpar Posted May 15, 2021 Author Share Posted May 15, 2021 (edited) 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 May 15, 2021 by marpar Quote Link to comment Share on other sites More sharing options...
Tony A Posted June 4, 2021 Share Posted June 4, 2021 Marco, Thank you very much for your time, response and schematic. I will look into this and get back to you if I have any questions Ciao Tony Quote Link to comment Share on other sites More sharing options...
marpar Posted June 14, 2021 Author Share Posted June 14, 2021 Hi Tony, I'm just glad I could help. Marco Quote Link to comment Share on other sites More sharing options...
Graeme Duffin Posted July 24, 2021 Share Posted July 24, 2021 hi. I don’t know if this post is still current, but I’d be really interested in a replacement preamp for the Chet Nylon string. This one hums and makes other noises. Any info greatly appreciated! Graeme Duffin Quote Link to comment Share on other sites More sharing options...
alimjan Posted November 5, 2021 Share Posted November 5, 2021 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 . If anyone needs such a preamp, I have 1 spare board that I can share. Marco The low noise (HUM......) on my Atkens is annoying. I hope your updated version solves this problem. Where can I buy it? Quote Link to comment Share on other sites More sharing options...
Johnny4nr Posted December 16, 2021 Share Posted December 16, 2021 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 1 Quote Link to comment Share on other sites More sharing options...
SdN Posted December 26, 2021 Share Posted December 26, 2021 Hi Marco is this post still active? I have the same issue, I can not fix the pre-amp and I am missing the scheme, any help would be highly appreciated. Ciao Stefano Quote Link to comment Share on other sites More sharing options...
SdN Posted December 27, 2021 Share Posted December 27, 2021 ... also because the link isn not active anymore and there is nothing attached here .... help ! 🙂 Quote Link to comment Share on other sites More sharing options...
marpar Posted January 13, 2022 Author Share Posted January 13, 2022 https://ibb.co/25Kq99H Quote Link to comment Share on other sites More sharing options...
Ricontheroad Posted May 27, 2022 Share Posted May 27, 2022 I have an 82 CE. Everything is great except the pickup ribbon has ripped right at the bridge. As far as I can tell, the ribbon is in yhe resin of the bridge. Any ideas from anybody would be appre iated. Cheers Ric Quote Link to comment Share on other sites More sharing options...
marpar Posted May 27, 2022 Author Share Posted May 27, 2022 Hi Ric, Is it completely silent (as I think) did I only work some strings? I know it sounds silly, have you checked the preamp battery? Marco Quote Link to comment Share on other sites More sharing options...
BDub W Posted January 31, 2023 Share Posted January 31, 2023 I am currently building my own SST style guitar. Do you know what preamp I need, or similar, as well as do you have any parts that you would like to sell? Quote Link to comment Share on other sites More sharing options...
marpar Posted January 31, 2023 Author Share Posted January 31, 2023 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. 1 Quote Link to comment Share on other sites More sharing options...
CGuitarSWK Posted February 21, 2023 Share Posted February 21, 2023 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 Quote Link to comment Share on other sites More sharing options...
CGuitarSWK Posted February 21, 2023 Share Posted February 21, 2023 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 Hello Marco. Is your preamp for the Gibson Chet Atkins for Sale? Quote Link to comment Share on other sites More sharing options...
marpar Posted February 22, 2023 Author Share Posted February 22, 2023 Hello CGuitarSWK, I'm sorry but it's not for sale. Quote Link to comment Share on other sites More sharing options...
Guitarman1 Posted April 6, 2023 Share Posted April 6, 2023 Hello, Marco can you share with us your PCB Layout design? Amazing work! Thank you in advance! Quote Link to comment Share on other sites More sharing options...
marpar Posted April 6, 2023 Author Share Posted April 6, 2023 I'm sorry, it's a long story, but I no longer have them... Quote Link to comment Share on other sites More sharing options...
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