Back in 2005, I was knee deep in DIY and having lots of fun with it. Granted, I hadn't been doing it very long, maybe a year, but I was learning quite a bit and started coming up with my own ideas. One of them was based off a circuit named the Fetzer Valve from Runoffgroove.
The Fetzer is based off the first input stage of a Fender amp. I decided to take that idea and make one that is the first input stage of a Marshall amp, which is where the name came from. It came out better than expected and so I decided to share it with the DIY community. Turns out that several folks like it and quite a few had been made, even by beginners. It's an easy circuit to make.
I still have one of the first ones I built and just recently started using it again. There's quite a bit of boost to it. In front of a clean amp, you'll get a noticeable volume increase. In front of a slightly overdriven amp, you'll still get some volume increase but it'll saturate the front end of the amp more increasing the drive. Pretty typical of a boost circuit. I like the bit of Marshall flavor it adds to the sound.
In the PDF below, the schematic, perfboard and veroboard layouts are included, as well as a couple photos of the completed circuit.