ProCo Rat Bass Mod

Everyone loves a big fat filthy bass guitar sound, and a lot of bass players use the Rat to get it.

I love the Rat, it’s one of my favourite guitar pedals, but the trouble for bass players is, that it’s designed for guitar, so it doesn’t act on lower frequencies as much.

Ben, the lead bass player in my band, gave me his old Rat with this request:

I’m just going to use it as a filthy tone on top of the SansAmp. So I need it to keep as much bottom end whilst still boosting the volume and breaking up a bit harder.

I hunted around online for a suitable mod, and found the perfect one: The Bass Bost Mod by GGBB. It works by boosting the bass without changing the sonic signature of the Rat.

Here is what I did to Ben’s Rat:

  1. Replaced the power socket with a standard 2.1mm “Boss style” one.
  2. Replaced the Red LED with an Orange one
  3. Added a 3 way switch to select: Stock, More Bass, or Even More Bass.

The Power Socket

This was a matter of removing one component and replacing it with another. Drilling a hole in the enclosure was the hardest part, literally – the Rat is thick steel.


The Bass Boost Mod

The mod involves adding a 3 way switch to select the amount of bass to let into the rest of the Rat circuit. Here is my layout based on the schematic provided by GGBB. When the switch is in the centre position, it is a stock standard un-modified Rat. To one side it adds more bass, and to the other it adds even more bass.

Here is the switch wired up, and also where it connects to the board:


The switch was a very tight fit!

Here is the finished product, with the switch installed:

Audio Sample

Here’s how it sounds!

  1. Off
  2. Stock
  3. More Bass
  4. Even More Bass
  5. Off