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March 19, 2024, 02:06:22 AM

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Marshall lead mosfet 100 lead channel very quiet

Started by buffalocomputer, May 19, 2021, 06:40:11 AM

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buffalocomputer

Just got one of these and a 60's 4x12 cabinet for $125, but the lead channel is extremely quiet. I can hear that it has the crunch, so I know that part of the circuit is good.


The amp does not respond to the volume knob on the lead channel, so I'm expecting it's a problem with the pot.

If turns out not to be the volume pot, what other components could cause that pot not to respond on the lead channel?

Also, what would be some good mods that I could add that I can make switchable with installing switches on the front plate?


Enzo

I suggest making the amp work before even thinking about mods.

Do nit assume it is a bad component.  It could be, but could also be a broken connection, broken wire, cracked circuit trace, etc.   Apply a signal and trace it through the channel looking for where it disappears.

My first reaction is a bad semiconductor somewhere.


Tassieviking

First thing to do is to find out which model MosFet you got, they made more then one model as far as I know.
Then i would find the correct circuit for it.
Try DrTubes website for the circuit to start with.
https://drtube.com/en/library/schematics/69-marshall-schemas
Once we know what you have we can make better guesses
There are no stupid questions.
There are only stupid mistakes.

Bjorn218

You have already pulled the grain pot out?  It's a push/pull. You also have to activate the gain channel with a TRS plug or was it TS, I can't remember just a plug where the foot switch plugs will do. That's what I had to do with mine.  It's a TS now that I think of it as I used a TRS plug and pulled it back out about a 1/4" to make the connection.