RAT bass mod?

[oczad]

I have a rat clone, one of those biyang mouse ones with the 3 position diode switch. I mainly just use it as a clean boost where the distortion is way down and the level to whatever amount of boost i wanna hit the amp with. I love what i get from it but theres no low end to speak of. I know RATs cut lows because the distortion gets farty, but since i use it as a signal boost rather then distortion i think adding bass would not cause a farty lows issue. So what i'm wondering is what the best way to add lows is. I assume there must be a post OD area to do that, but if not i think a pre OD area would be ok considering how i use it. Any ideas? Circuit seems to be pretty straight forward RAT aside from the diode switching. (also, i use it with diodes set to none)

[ElectricDruid]

The highpass filtering is in the gain stage. There are two "legs" in the gain circuit, each with a different cap.

Here's the "MultiRAT" schematic:
<EDIT>Please see Gord's post below - my link was an old image from the interwebz</EDIT>

We're talking about C6 and C7. C7/2u2 has more of a bass-limiting effect than C6, with a roll-off around 1.5KHz (according to Electrosmash, who are not generally to be trusted without crosschecking).

The simplest way to improve bass would be to simply remove that 2u2 cap which would disable that leg of the gain.  That leaves the other side which is a lot less bass-cutting (60Hz - same caveat) and should fatten up the bottom a lot.

HTH

[oczad]

thanks, i'll look into this.

[Fancy Lime]

Awww Rats! I read the Subject and thought I'd get an opportunity to ramble on about how to turn the Rat circuit into an actually great bass distortion. Two-band tone control and all. Oh well, maybe some other time.

EDIT: as for your actual question and purpose, I'm with Tom. Cut that 2u2 cap and you'll have a lower gain Rat with pretty full range sound for use as a clean boost. To me personally, that seems a rather peculiar use case for a Rat, but it does seem to be a popular one.

[GGBB]

Most recent Multi-RAT schematic:



My personal recommendation for improving bass is my "BB" mod:



It's still sounds like a RAT but gives more deep bass. If you're just doing clean boost you might want to try Tom suggested.

[Rob Strand]

My personal recommendation for improving bass is my "BB" mod:

FYI: You can actually simplify the switching on the first two circuits by simply connecting the second RC network in parallel with the first RC network using an SPST switch.   Paralleling the caps does nothing when the RC products (or pole frequencies f=1/(2*pi*RC)) are the same.   In the 270R case there is a very minor difference in response as 270R isn't quite 560R/2 and 10uF isn't quite 2*4.7uF but it's all academic - I only mentioned it in case you see a small difference on an LTspice sim.

[GGBB]

Paralleling the caps does nothing when the RC products (or pole frequencies f=1/(2*pi*RC)) are the same.   In the 270R case there is a very minor difference in response as 270R isn't quite 560R/2 and 10uF isn't quite 2*4.7uF but it's all academic - I only mentioned it in case you see a small difference on an LTspice sim.

The mod is deliberately designed to keep the knee frequency the same while raising the gain. It actually sounds really great IMO - keeps the characteristic RAT tone while increasing low bass. And there is a clear sonic difference at "270R/10uF" "560R/4u7" although not as obvious as the greater setting. Try it - you'll like it!

[Rob Strand]

The mod is deliberately designed to keep the knee frequency the same while raising the gain. It actually sounds really great IMO - keeps the characteristic RAT tone while increasing low bass. And there is a clear sonic difference at "270R/10uF" although not as obvious as the greater setting. Try it - you'll like it!

I get the idea.   All I was suggesting is it possible to simplify the switching.



Some similar tinkering was recently done here,

https://www.diystompboxes.com/smfforum/index.php?topic=130948.0



This simulation shows the response V(VRAT2) and V(VRAT2B) with the bridged caps are identical - Cyan trace underneath Dark Blue trace.



Please forgive the specific part values.  The frequencies are the same as the RAT and your RAT bass boost mods.  The impedance matches the TS9 which continues from the thread I linked.

And of course you can see the effect of your mod boosting the bass.