Marshall MG100DFX Help Please!

[roboticsdoctor]

Hello Gents,

I just picked up a free MG100DFX from a friend and I believe the IC is bad. While I was poking around in there, it appears that there is a green and red LED that are used for the clipping circuit of the overdrive channel. Any major problems if I replace them with some germanium diodes like a pair of opposing 1N34A diodes? I did this on a Crate head and it sounded amazing! The setup was a little different in the Crate, so I thought I would get some input from yall.

Thanks!

[Mars Amp Repair]

Probably better if you start a new thread. I'm not certain where those clipping LED's are in this amp but in some of the older ones, you can just remove the diodes all together & you'll get a much more natural distortion than the buzzy type you get from this type of circuit. I'm sure the other guys will know better...glen

[man of wheel]

Diodes to billy jo (lol)...ode to billy jo movie

Probably better if you start a new thread. I'm not certain where those clipping LED's are in this amp but in some of the older ones, you can just remove the diodes all together & you'll get a much more natural distortion than the buzzy type you get from this type of circuit. I'm sure the other guys will know better...glen

Hi I am the "new" "nooby" on here
ANY Ways on here trying to fix my my marshall Mg50dfx cause I pulled a real bone head!! Neghbor next door started cranking up Super Stereo over me playing my acoustic. So I thought Oh, thats how it is. You want to play with power , huh? I hooked my300 watt bass amp, and why dont I hook another speaker to that ( I thought... instead of hookig up the speaker which is the male part,Noooo! I plugged into the female, which in reality, is the brain. When no sound came did the double check and discovered what I had did. Since then I turn amp on and it blow fuse so fast I can"t check anything so when I read this, This I think this might be the problem I hope. Also it was mentioned about the red and green diode. I got those on my amp as well and quite frankly, not really happy with the distortion. and since I am at it not real pleased with the reverb as well.
Nice to meet you all, i will appreciate any help. Thank You

[The Dude]

Ok, first, you'd be better off starting a new thread for your amp instead of tagging it on to one from 2009.

If I read your description right, you plugged amp to amp, so the most likely scenario is that you blew up the output IC. In the very first post of this thread there is a picture of the output module that contains the output IC. Unplug that little board. Put in a CORRECT VALUE fuse and see if it holds. Let us know what happens.

[audiopete]

Probably better if you start a new thread. I'm not certain where those clipping LED's are in this amp but in some of the older ones, you can just remove the diodes all together & you'll get a much more natural distortion than the buzzy type you get from this type of circuit. I'm sure the other guys will know better...glen

You can for sure try to replace the clippers with Ge diodes. Some amps use a diode bridge rectifier package for clippers. The clipping will be fuzzier and start earlier due to the lower forward voltage of Ge diodes. For the "Marshall" sound, LEDs are usually best there.

Another mod I like with those amps with the built in clippers is to increase the series resistor (double it) in the signal path before the clippers (lowering signal gain), and decrease one after the clippers for more natural overdrive and less fizz (or mod the gain stage itself for more PI drive - amp dependent). It turned a fizzy Marshall 2205 into a decent facsimile of a plexi.