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Alembic F2b meets KLON Centaur = Frog Fx1 Tube Preamp

I want to point out something that I very intentionally did, but really haven’t emphasized much at all and that is in regard to the 2 diode clipping options on the Frog Fx1 Tube preamp pictured below.  The clipping options were not in the Alembic F2b preamp or in the original Fender circuit.  I had some room available on the printed circuit board (PCB) when I designed it and decided I would add some diode clipping options to give a little bit of fuzz or overdrive tone to the preamp.  I was familiar with the Klon Centaur that was designed in the 1990’s and had built a clone of the circuit and liked the mild overdrive tones it gave me with guitar.  So, I researched the circuit diagram of the Klon Centaur (it is not tube based) and found where Bill Finnegan placed the pair of clipping diodes in the circuit.  They were right after the first opamp buffer stage and Bill only included one clipping setting.    So having found where they were placed, I tried placing the clipping diodes right after the first preamp stage of the Frog Fx1 (there are 2 preamp stages in the Frog Fx1) and found that they worked great in that position.  There were a couple different types of diodes I liked that gave distinctly different clipping characteristics so I added 2 different clipping options.  One is more of a mild overdrive and the other is a mild fuzz/distortion tone.  They are very touch sensitive, so their influence on the sound is related directly to the output/string attack of the instrument used.  I am sure there are many more that would sound great, but I only had so much room on the PCB.

Just so you know the street price of the Alembic F2b is about 1300.00 and the KLON Centaur has truly become mythological and runs between $2000.00 and $3500.00 when you find used ones online.  Makes the price of the Frog Fx1 downright reasonable!

Alembic, Fender, and KLON are the property of their respective owners.

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Frog F1a Tube Preamplifier PCB for DIY

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Class A vacuum Tube preamp based on the Fender Dual Showman preamplifier section which inspired the Alembic F2b preamp. It is high quality 1.6mm board with 2 ounce copper traces (double the normal printed circuit boards) with Gold plated solder pads.