Hello,
I wanted to make some mods on a Marshall 4210 combo (it sounds quite harsh...), but the circuit doesn't match the classic schematic that I found everywhere on the web and on the Tube Amp Book. This schem is from 1983, and my amp seems to be a later model (1988/89 I think). The amp doesn't have the transistor switching circuit (it's IC based), and it has a 470K plate resistor on the first lead channel tube.
Does anybody know a bit more about this amp and where I could find the schematic ? If someone has it, I would gladly have a look at it.
Thank you.
Cyril.
Marshall 4210 Combo, late model schematic
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iknowjohnny
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Re: Marshall 4210 Combo, late model schematic
The link below is direct link to the 4210 schematic. The one you are probably finding is the single channel model. Your channel switching model (and by the way i had 3 of those) uses diode clipping distortion which is probably what you hear as harsh. You can remove them and change the preamp gain structure pretty easily to get more real tube drive after removing the diode clipping.
http://www.schematicheaven.com/marshall ... w_4210.pdf
http://www.schematicheaven.com/marshall ... w_4210.pdf
Re: Marshall 4210 Combo, late model schematic
Thanks for your answer, but it's actually the usual 1983 schematic I found.
My amp is later and has a completely different circuitry (tone, clean and lead channels, and an IC switching). I could redraw it, but it's boring....
There should be another schem, Marshall made a lot of different circuits for JCM800 models.
My amp is later and has a completely different circuitry (tone, clean and lead channels, and an IC switching). I could redraw it, but it's boring....
There should be another schem, Marshall made a lot of different circuits for JCM800 models.
Re: Marshall 4210 Combo, late model schematic
CB, It looks like we are both working on Marshalls! If you get me a little more information on your amp, perhaps I might come across one while sifting through schematics for my own. What's the serial number btw? That would help.
I would like to see the schematic for yours before giving advice...but I agree with Johnny, take out the hard clipping diode pair as you can do so with out risk to your circuit board. It'll take of the layer of distortion your probably experiencing and not liking. It would do wonders. But that still won't help your clean channel. That has to do with filtering that's probably happening before the eq.
Is there a Cap across your 470k resistor? If so its acting as a high pass filter. Try removing the cap, and swapping out the resistor with a 68k to not let the circuit run unattenuated. I did this on my 79' JMP as it had the 470k resistor w/ cap before the tube and it warmed things up a bit.
Good Luck!
I would like to see the schematic for yours before giving advice...but I agree with Johnny, take out the hard clipping diode pair as you can do so with out risk to your circuit board. It'll take of the layer of distortion your probably experiencing and not liking. It would do wonders. But that still won't help your clean channel. That has to do with filtering that's probably happening before the eq.
Is there a Cap across your 470k resistor? If so its acting as a high pass filter. Try removing the cap, and swapping out the resistor with a 68k to not let the circuit run unattenuated. I did this on my 79' JMP as it had the 470k resistor w/ cap before the tube and it warmed things up a bit.
Good Luck!
Re: Marshall 4210 Combo, late model schematic
Hi,
The serial number is X30379. I think it's from 1989, LCR caps are marked 89-29 and the Drake transformers 10-89. I live in france, so it's perhaps a european production only (?...)
It has nothing to do with 70's or early 80's models, it's a lot worse... I began to redraw the circuit, fastidious job ! the locations of the components are completely mixed, with a lot of copper pathes on the circuit board...
But the schematic seems to have a really poor conception quality. The tone circuits are cheap and esoteric, some engineers certainly wanted to "invent warm water" (a french wording
) And the clipping diodes of course !...
I bought this amp to eventually build another one with the parts. I will achieve to trace the schematic to see the intricacy of Marshall engineers, and then I built a good old circuit with good components !
The serial number is X30379. I think it's from 1989, LCR caps are marked 89-29 and the Drake transformers 10-89. I live in france, so it's perhaps a european production only (?...)
It has nothing to do with 70's or early 80's models, it's a lot worse... I began to redraw the circuit, fastidious job ! the locations of the components are completely mixed, with a lot of copper pathes on the circuit board...
But the schematic seems to have a really poor conception quality. The tone circuits are cheap and esoteric, some engineers certainly wanted to "invent warm water" (a french wording
) And the clipping diodes of course !...I bought this amp to eventually build another one with the parts. I will achieve to trace the schematic to see the intricacy of Marshall engineers, and then I built a good old circuit with good components !
Re: Marshall 4210 Combo, late model schematic
Right on! I've in the process of finishing up some mods to my 79' JMp and after all that fun I'm thinking of buying my friends Peavey VTM 60 to gut and have some fun with.
With that combo you'd have plenty of guts to build what ever you want. and good luck to you in both building something nice and old / deciphering your circuit board
With that combo you'd have plenty of guts to build what ever you want. and good luck to you in both building something nice and old / deciphering your circuit board