Apologies in advance for the long post, feel free to skip to the pictures if you'd like!
After lusting for a modified Marshall for a long time, and being quite the tech head/nerd when it comes to everything guitar related, I decided to modify my 1981 JCM800 2204 to no longer be dependent on any overdrive or boost pedals. My modding experience is fairly limited, it started a couple of years ago with the 'British Glory mod' on an Orange Tiny Terror, which went fine. Then I tried to modify a 1987x to a 2204 circuit, which ended quite disastrous and my local amp tech had to spend so much time cleaning up my mess that it cost me £160... After that fairly discouraging experience I didn't do much more, until I did the BG mod to another Tiny Terror, and again there were no issues so I gained a bit of a confidence boost again. But then I scored a cheap Vintage Modern, which I didn't really like, but I found this guide on the Metropoulos forum which supposedly would turn the low dynamic range into a Plexi, and the high dynamic range to a JCM800. Which again, ended disastrously, f*cked up a trace in the circuit board which luckily was just going to ground, but luckily I managed to sell it for a decent loss.
Fast forward to the 2204: It sounded really good stock, but as you know a cold clipper in a 3 stage design doesn't yield a lot of gain, and an extremely uncompressed character that is really nice for classic rock like AC/DC, but not particularly for heavier stuff unless you boost it. After struggling with a *bunch* of overdrive pedals not giving me what I wanted, on top of despising the fact that even if I found a good one I would still be dependent on that pedal to get my sound, it was quite a nobrainer really. Started out with the regular 'warming up the cold clipper' with a 4.7k cathode resistor, which was a great mod and something I would recommend to any JCM800/JMP MV owner. Then I started experimenting with Jose type circuits including the Cameron Atomica and Friedman BE. Atomica sounded really good, BE not so much but I think I might have done something wrong....
Being a quite massive Green Day fan I have been researching the Dookie mod for longer than I can remember, but apparently the schematic floating around is incorrect so I didn't bother trying it. I did, however, find a schematic for the Custom Audio 3+SE preamp, which sports the circuits for the Lead and Crunch mods. The SE Lead is not very versatile, it doesn't clean up particularly well with the guitar volume or gain knob (probably because there's 3 gain stages after it) but man does it have *that* sound! By "that sound" I mean what my head/ears imagine the 80s to sound like, haha!
Next up is my Marshall JMP from 1972, that has been modified with the Crunch mod! Just need to get some Mustard caps to at least attempt to trick people into thinking that it's stock
It has been pretty much a rebuild, I'm sure you can identify what is stock and what is not
