Technical Question for Marshall Modders

[tonmazz]

I'm undertaking my first attempt at modding a Marshall JMP 100 and so far it's coming pretty good. I've been following the Ultimate 800 mod from the tone lizard site below:

http://www.tone-lizard.com/Ultimate_JCM800.htm

My questions are more for my own understanding more than anything. They deal largely with the treble peaking circuit and there are two they refer to in this mod. Definately gave the amp more gain but it seems to be taking me in a dark direction as I follow each step. Specifically the removal of the Capacitor on the circuit board I'm not sure if i like that result. I like the added gain and want to play around some more but I was curious if this was a common place to start when modding a marshall and what these treble peaking circuits are supposed to do. I would also like to hear some other opinions and ideas of other areas to play with or things that have worked. Not asking for anyone to give away any secrets, but I know there are basics that can be shared. Any help or advice is appreciated. This is a ball playing around with this stuff.

 

[James Lugo]

Man you are a daring man. I would be so afraid to f around with a JMP myself. You should email Friedman, Cameron or Fortin. I know Mark can be hard to get a hold of but he's a good dude but Dave and Mike are pretty accessible. Dave's my guy, he's a bad mofo with Marshalls.

 

[duesentrieb]

If you make a list what you've changed from stock specs so far, I'd be glad to "help".

 

[tonmazz]

If you make a list what you've changed from stock specs so far, I'd be glad to "help".

Thanks!! Check out this link, I followed steps 1 through 4 so far.
http://www.tone-lizard.com/Ultimate_JCM800.htm

I've found that removing the bright cap, seemed to be a good move. The cap across the resistor in step #1 I have to swap back and see the difference. The different resistor value seems to be good. The biggest change in tone for the worst was removing the 500PF cap on the board in step 3, I think it robbed to much treble. Dropping the value of the resistor in step 4 seemed to add some more nice saturation but I want a bit more treble at this point. Thats where I'm at. My next step was going to be to put back the 500PF cap to see what that does. I also had some great advice from others that I'll be trying as well. Any advice is welcome. Thanks.

 

[tonmazz]

Man you are a daring man. I would be so afraid to f around with a JMP myself. You should email Friedman, Cameron or Fortin. I know Mark can be hard to get a hold of but he's a good dude but Dave and Mike are pretty accessible. Dave's my guy, he's a bad mofo with Marshalls.

James,

Hey man! You know, I greatly respect those three guys having owned a Cameron and had some great advice from Mike who is a 100% class act and his stuff sounds killer! Never had the pleasure of owning a Friedman but on your vids they sound great. I just want to try and do this for my own knowledge so I can stop spending $2000 everytime a nice new hot rod comes along. I am an amateur and have no aspirations to anything but understanding how to affect the tone, saturation, etc for my own enjoyment. It's pretty awesome so far and I'm starting to see how different areas of the board affect tone, saturation for better and worse. See what happens when you're bored!! At the end of the day, maybe I'll have something I can tweek to my liking and learn a thing or two along the way. We'll see. The other neat thing is that I picked up a beat up, on the outside, JMP for $600 and it needed a few minor things to get back to stock and thanks to 232cap for helping me with that. Now I can take it from there. I'll keep you posted and maybe post a clip or two when it's all done. No making fun!!

 

[duesentrieb]

If you don't want to reinstall the 470pF of #3, you can also solder a 220k from the middle of the gainpot to ground (freshens up the sound again). Also the 470k (before in parallel with a 470pF cap) could be nicely replaced with another 220k for a bit more gain, but without that "tiredness" of the original 470k.

If you don't have 220ks, keep it as it is now and solder the 1nF (1000pF) which you took off the gainpot to the "#3-470k" in parallel, thats a nice upper mid-gain hump you may like.