Hey some of you mod guys out there. I want to add a mod to a Tweed or a JTM that would allow the switch to be made between the two by pulling out the gain pot or other pot or switch. After looking at the two circuits I see that they are nearly identical other than two Capaciters-C2 and C4 and one resistor R28. I need a kit that will allow me to change from one sound to the other by pulling out on a knob or modding the bright switch. One of the capicitors looks like it is used with the bright switch as well. I am currently setting up a spread sheet that will show the differences between the Caps, Resistors and Pots. If the mod will work I think we could open up many more tones in each module or at least modules with similar circuit designs. I have built a few stompboxes so I am fairly handy with an iron. I do have a variable temp digital soldering station. I just don't understand all of the signal flow on the modules yet. Any help on this?
Tweed to JTM mod
- Thread starter ak37
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I have ordered the parts I need to make the mod but I am going to make it a Plexi. I will have it to where I can switch back and forth on the front of the module. I have it figured out. I will keep you guys in the loop as to how it works out.
ocaptainjr2
Active member
Sounds very cool! Please post a list of parts, or a 'how to' when you are done because I would definately want to give this a try.
I have been putting together a spread sheet based on the board layouts on the grailtone site of all of the various resistors, caps and their locations on the respective pcb's. I have found a source of a 4pdt switch that I will use to do this mod. The switch will mount through the front panel to switch between the tweed and plexi tones. The main differences between many of the tweed, jtm, plexi tones are in the resistors and capacitors. The easiest being between the Tweed and JTM with the original circuits being so very close, these are as well. I love the plexi sound but I also love the tweed as well so I am shooting for a mid complex mod at first instead of the simple first. What the mod will be is removing the resistors and capacitors from the stock tweed board that are different than the plexi module. Those will be populated to a small pcb from radio shack. Beside these components the respective parts for the plexi will be added and then solder the ends together on one end and that output will go back to the main pcb to complete the connection where it was removed. The output from each section will come up from the tweed pcb to the input on the switch. Each output from the switch will go back to the respective resistor and capacitor on the R/S pcb. The switch will have four inputs and eight outputs, so four changes will be made at one time. Don't forget to add the cap for the tube board for the plexi section to the switch as well. I will make some drawings and some pics of this to aide in understanding this mess.lol
I have my parts ordered and my schematic drawn up. My module is on its way. Maybe I won't blow something up. lol. I couldn't find an off the shelf 8PDT mini switch so I got two 4PDT mini's to use instead. One will switch the resistors and tthe other will switch the capacitors.
Shinozoku
Well-known member
I thought about doing something similar, but hopefully making it go from a Deluxe, to a Tweed, to a Plexi. Maybe a 3 position bass cap, then a couple more switches for the other stuff, and a push/pull pot for clean/medium gain. might be a bit over the top though 
I can't wait to hear how this turns out
I can't wait to hear how this turns out
It lives! It lives Igor! I got the mod finished today and got it right the first time! I love it when a plan comes together. The stock Tweed on one side then hit the toggle switch and banf, JTM! I love it and recommend doing it to any tweed or a JTM. It is only a 3PDT mini toggle, two resistors and four capacitors and you have a dual module at the flick of the switch. Anyone wanting the info for this hit me up.
crankyrayhanky
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That's awesome! Post some clips if you can
The Tweed and JTM are probably even more similar due to the fact that the original JTM was a tweaked copy of the original Tweed amp to make the Marshall sound. A little more gain and a little brighter. That is how this mod is too.
I went to straight up plexi. I need a signal flow diagram to make it work. If anyone has any thing like a signal flow diraction mapped out for any module I really need it. I was able to remove the switch mod intact so once I get the path mapped out I will know exactly where to make the to and from routings correct. I am diggin the plexi tone too much to do with out it right now. After I removed the switches I had two left over holes in the faceplate so I made a new one from some thick gold plexi and added a purple led. I have some pics I need to post.
