The Four Knob Rat: Tech Stuff and History

This page contains misc stuff about the development of the FKR.

Build Your Own FKR!

Here is a PDF with the schematic, layouts, wiring diagram and parts list for the 1.12 Revision.

The Metal Can

The typical LM308 opamp is the standard black plastic 8-pin DIP package. But it also comes in a great metal can version, the LM308AH:

I have procured a bag of these and will test them out to see if they sound any different then the standard LM308. If nothing else, they certainly look cooler, in a geek kind of way.

FKR Prototype #2

Prototype 1 was so ugly I refuse to post a picture of it. So we'll move straight on to proto #2. Ugh. Still a mess. But it sounds heavenly. You can see the various clipping diodes solder to DPDT switches. This build also had an experimental pot to fine-tune the gain structure, but that mod actually did nothing of use so it was tossed.


I had ordered some very cool cast metal chrome-plated Skull knobs for this project. Here's what they looked like on Proto 2:


There were two problems with this knob choice. First, they are huge, so you can't rotate one without it knocking into its neighbor. Second, they are ridiculously expensive--about $15 a piece. So that would have added 60 bucks to the project.

FKR Prototype #3

After some work in component placement and working up a front panel design I was happy with, the pre-production prototype #3 is done. Getting closer, and it all still fits in a 1590BB. The top graphic was printed on inkjet glossy sticker paper, cut to size and stuck on the front of the box. Three coats of clear polyurethane keep the whole thing relatively protected.

The exposed toggle switches are a problem--one errant stomp and you've busted a toggle off. I'm working on various roll-bar ideas to solve this problem, probably something like this:

Here's a Mark One being built:

The BYOC Mighty Mouse had a fantastic RAT clone kit. I used BYOC boards for the first few runs and had fun creating a mod sheet so you can apply the FKR mods. Check it out. BYOC Mods

Stock Rat Schematic

For comparison purposes...

Stock Schematic