The Making of the Fat Rat
I bought a ProCo Rat and after some testing I decided that I did not like it too well because it had a harsh edge that did not go well with my playing style. It was either sell the box or modify it to produce a better sound and after some deliberation I had formulated a plan. The idea that I finally settled upon was to revise the circuit to make it conform to my Fat Gnat design as near as possible. The original Fat Gnat circuit was published in RECORDING magazine in the October 2000 issue and is available on the AMZ CD-ROM.
Since there are numerous basic similarities between the two circuits I was able to incorporate most of the elements of the Fat Gnat into the modified ProCo box. Listed below is a summary of the changes that were made to the circuit.
Furthermore, when the "Distortion" knob is set to its minimum, the Rat now acts as a clean boost! - It's no longer a one-trick-pony. At moderate gain it has a lot of the sound of a Tube Screamer without the mid-range hump (i.e. flat mids). It has slightly more maximum gain than before but with all of the harshness removed.
The modifed Rat can now do clean boost, blues drive and full tilt boogie! What a change in sound these mods have made... it sounds like a totally different effect!
BTW, do not be tempted to run the original Rat at voltages higher than the stock 9v. The power supply filter cap is only rated for 16v and higher values could damage the unit.
NOTE: I am modifying the Muff-Rat eBook to include a schematic that shows all of these changes in detail so that you can make your own Fat Rat.
Update Aug 2017: My Kindle ebook with new information on the Rat and the mods is now available from Amazon:
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