Build RAT with more dynamics and attack.

[boris]

Hi all,

I would like to build a RAT but with more attack and better dynamics.

I am already thinking of switching to an NE5534 instead of the LM308N.

What can run up to 18v for a little more headroom I think.

Do you have any ideas concerning modifications to be made to increase the dynamics and the attack (value, type of component, etc ...)?

Thank you in advance.

[bartimaeus]

sounds like a turbo rat to me, which is just led diodes instead of silicone. that will add a lot more headroom than swapping the opamp. if that's too dramatic a change, you could experiment with other clipping diode options to get you somewhere between turbo and standard rat.

also, have you seen GGBB's multi-rat diagram?

https://www.diystompboxes.com/smfforum/index.php?topic=122468.0

[Mark Hammer]

Hi all,

I would like to build a RAT but with more attack and better dynamics.

I am already thinking of switching to an NE5534 instead of the LM308N.

What can run up to 18v for a little more headroom I think.

Do you have any ideas concerning modifications to be made to increase the dynamics and the attack (value, type of component, etc ...)?

Thank you in advance.

What you're describing stops being a Rat.  That's not necessarily a bad thing, but it makes about as much sense as saying you want to build a Rat that is super clean with wide bandwidth.  In other words, you're adding transformations that turn it into a different device.

Using an 18V supply (and make sure all relevant electrolytic caps are good with that) will certainly increase headroom.

A standard Rat uses the dual ground-leg approach which provides noticeably more gain for upper mids and highs than for the frequency content below that.  I'm not sure how much more "attack" you might expect to get than what the standard circuit delivers.

One thing you could try is to replace the back-to-back pair of silicon clipping diodes with a pair of red LEDs, as bartimaeus suggests. They won't clip in an especially different manner, but they will have a higher clipping threshold, such that they won't clip unless you dig into the note. That will provide hotter maximum output, and more dynamics.  Were you using an LM308 and 9V supply I doubt they'd sound they way I'd expect, using a 5534 and 18V supply. 

With the gain applied in the stock circuit, and the limitations of the 308, especially when using only 9V, part of what you're hearing is clipping from the op-amp itself, which is then RE-clipped by the diodes.  With a 5534 and 18V, the brunt of any clipping you hear, until the gain is pretty well dimed, is from the LEDs alone.

The stock Rat circuit uses a simple single-pole lowpass for its "Filter" control.  Effective, but maybe a slightly more flexible tone control might get you a wider range of sounds.

You can see below that the "Filter" control is simply a variable 100k resistance with a 3n3 cap to ground.  The larger the resistance posed by the pot, the lower the cutoff frequency of the filter.  Ordinarily, the Filter pot would interact with the volume pot such that more treble cut would result in less volume as well.  The FET buffers and isolates the Filter control to sidestep that problem.

But let's try this.  Instead of connecting C8 to R8, let's cut that connection (leaving R8/C9's connection intact), and have the wiper of the Filter pot connect to C8 instead.  That leaves the full 100k and 1k5 in series.  Moving the Filter pot still changes where the treble-cut begins, in the exact same way.

So, what's the advantage of doing that?  Well, straddle R7/R8 with a cap, like you see in the bottom redrawing (thanks to electrosmash for the original drawing) and you've turned it into a variable-scoop filter, with plenty of sizzle.  Since you don't necessarily always want the extra sizzle, we'll add a simply on/off toggle for the added cap.

Note that since your plan is to use LEDs, and 18V on a 5534, I've drawn it as that.

[antonis]

What you're describing stops being a Rat.

Nothing to add...

[GibsonGM]

Welcome, Boris....sounds like you need a good tube amp and a mosfet boost   

[antonis]

a mosfet boost 

Just a clean boost, Sir..
No clipping, no distortion, no odd harmonics, nothing..??

[niektb]

If it compresses too much, you could also try reducing some bass , for this you could play around with the values from R4 and R5

[Gus]

Do you mean an expandora?