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Topics - CraftyZA

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Tubes and Hybrids / Rebuilding Marshal Amp
« on: March 25, 2015, 02:39:11 AM »
I'm rebuilding a marshal valvestate S80 amp. The one with the 2 x 12" drivers.
I'm going to rip out the current amp portions and only use the chassis and drivers.
I've got the new power stage sourced. I can decide between a veloman kit amp, or lm3886 based amp designed by a friend of mine.
However...
The preamp and overdrive is still a headache. I need to understand the dynamics before i can design it.
The idea is to use an 12ax7 valve for that. possibly 2.
The input signal on the power stage is set to max 2v. This i quite high. I can adjust to about 1v
Do i need 2 stages before that? IE normal preamp, that will be overdriven by a 2nd preamp? Or do i just give one preamp a very large gain range from clean to crunchy?
Any one got simple circuit diagrams for it?
I've bought an extra 12ax7 tube. Plus I have the one that can be salvaged from the original valvestate amp.

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