Building a Rat (GGG Rodent) - What should i know?

[RacerR]

So I completed my first build last weekend, and I'm now ready to start on a GGG Rodent kit.

I know the  original Rat pedal was equipped with a LM308 op amp, while the GGG kit comes with an OP07C.  I'm not sure what if any impact changing the op amp will have on the sound.

I also noted that the clipping diodes in the original Rat schematic are 1N4148 , but the GGG schematic shows 1N914.  Again - I'm not sure what this does to the sound.

I'd appreciate any thoughts or insight you guys may have on this.

For the above, I refer "Original Rat Schematic Rev B" and to the following versions of the GGG Rodent docs:
BOM: Version 2010January10
Layout: Version 2012January20
Schematic: Version 2012January20

Thanks.

-R

[rousejeremy]

I haven't heard the op amp they provide so I can't comment there.
1n4148 and 1n914 are both silicon diodes with the same forward clipping voltage and are can be substituted one for the other. The Turbo Rat uses Germanium diodes, 1N34a.
Check out some mods here. http://www.beavisaudio.com/projects/fkr/images/MightierMouse.gif
Here is a great schematic covering all versions. http://www.aronnelson.com/gallery/main.php/v/diyuser/GGBB/Multi-RAT.png.html

[Jopn]

With the LM308 it sounds like:
Drrrrrrrggggg Dgug Dgug Dgug

While OP07C is more of a:
Grrrrrrrrggdgg Dgig Dgug Dgug

If your really that curious on exactly the subtleties between the two, it'd be worth buying other opamps to swap and hear for yourself.  From what I understand, online descriptions of sounds and tones are sometimes not a 1:1 match to the sonic timbres they represent.

[GGBB]

The Turbo Rat uses Germanium diodes, 1N34a.

Actually that's the You Dirty RAT.  The Turbo RAT uses standard 5mm red LEDs - this is my personal favourite (at the moment anyway).  A great mod is to have all three diode options on a toggle switch.

[rousejeremy]

The Turbo Rat uses Germanium diodes, 1N34a.

Actually that's the You Dirty RAT.  The Turbo RAT uses standard 5mm red LEDs - this is my personal favourite (at the moment anyway).  A great mod is to have all three diode options on a toggle switch.

Don't know how I screwed that up. Thanks for the correction.

[GGBB]

There's another way to bias the output FET instead of using GGG's "add-on" - the way it is done in the Turbo RAT.  Using the GGG kit, you would jumper R9, use 2.2M in R12 and R13, and leave out C14.  I'm not sure that one is better than the other, but the Turbo RAT version is at least Pro Co original.  Incidentally, the Turbo RAT would also use 2.2M instead of 1M at R1 and R17.

[RacerR]

Check out some mods here. http://www.beavisaudio.com/projects/fkr/images/MightierMouse.gif
Here is a great schematic covering all versions. http://www.aronnelson.com/gallery/main.php/v/diyuser/GGBB/Multi-RAT.png.html

Thanks Jeremy - those links cover exactly the information I was looking for.

-R