Fat Rat & Metal Rat mods for bassists

[Ocoaibass]

I have been looking through the AMZ ebook on Rat mods & am curious if any of you have done these mods. The text seems to be geared towards guitarists, which leaves me slightly dubious as to their applications for bassists, which is what I'm using this for.

The Metal Rat seems to introduce a mids scoop, ala Big Muff, but I can't tell how much that would differ from the Filter knob as I'm still rubbish when it comes to reading schematics.

The Fat Rat seems to turn it into some sort of overdrive, which to me, sounds like a step in the wrong direction. I use a Rat to get aggressive & grindy, but a little better articulation may be fun.

That being said, I'm intrigued by the whole compensation cap and op amp situation. He suggests changing to a 5534 or TL071 & removing this cap. If I double stack LM308N chips, would I want to remove or keep this cap?  I know that the cap is essential for the LM308N on its own, but again, I haven't the knowledge to decipher for myself whether or not I'd still need it with TWO of these chips double stacked.

Lastly, has anyone tried any part or all of one of these mods or op amp changes? I am very curious about the chip swaparoo as I've got mine socketed & it would be easy to play around, just not cheap since I'd have to buy some more chips.  TL071 chips are available locally to me, but the 5534 is not.  Of course its only 3 days away from any online order.

[azrael]

Changing to a normal opamp, instead of the externally compensated 308, IMO, is a step in the wrong direction if you like the "RAT" sound. The slew rate distortion from the 308 is responsible for the Rat's signature sound.

Adding a midscoop, if you are a bassist, is also a step in the wrong direction, IMO. Bassists have a hard enough time cutting through without adding a midscoop.
The filter now is a simple low pass filter, meaning it just cuts treble. The BMP tone control pans between a low pass and high pass filter, and the middle just always ends up scooped because of this.

If you want more open and articulate clipping, consider changing the clipping diodes to something with a higher voltage threshold. Perhaps 1N4001s or red LEDs.

I don't know if stacking a 308 is a good idea. I thought stacking opamps in parallel was cool, but then I realized that you are almost halving the input impedance, as well.

[Ocoaibass]

Yeah, I thought the same thing about the mid scoop. As for the 308 chip, I'm going to try the stacking, just for fun, but definitely not the swap. You & several other people (on talkbass forum) have said the same about the 308 being essential.

Thanks for the idea of changing diodes. I've considered the Beavis Audio 3 way toggle mod. It does stock diodes/MOSFETS/red LEDs which sounds like lots of fun options. I may swap out the stock diodes for 4001s first, just to see if maybe I like them better. That way if I build this new clipping circuit I will have several options more.

Thanks for your input. I'll let you know how it goes.