Which RAT circuit to build?

[mremic01]

Hi all. I'd like to build a RAT clone, but I'm not quite sure which circuit to go for. It seems to me like the GGG schematic is a little different from the Tonepad one (10k resistors instead of 100k and a .047uf cap instead of 1uf). Tonepad's seems more consistent with this one: (http://www.happybob.com/rstrand/rat/pcratrev.gif). Some bands I like from the mid 90s used RATs, so from what I can tell I should be copying a RAT2 circuit?

Could anyone lend some insight into which would be more what I'm looking for, or which one is correct.

Thanks in advance.

[tubelectron]

mremic01,

1/ You have reach the right information source (http://www.happybob.com/rstrand/rat/pcratrev.gif).

2/ I found that the best RAT is the 1981 rev.B circuit. It uses an LM308N, and no IC than this one sounds better in this circuit. The clipper uses 1N4148, not Leds.

3/ To built my RAT, I bought an used Vintage RAT RI (post-2003, big box model, discontinued today, S/N°:VR-114590, USA made), and modified it to return to the 1981 Rev.B circuit, which is easy to do. My Vintage RAT RI PCB is labelled : PRO CO SOUND inc. RAT3 REV.B SEC-5-0, so the transformation from a more recent RAT( 2 or 3) to the 1981 Rev.B circuit is possible.

4/ My Vintage RAT RI was fitted stock with an OP07DP IC, which sounded like any standard distortion, and the changeover to an LM308N improved greatly the sound, while the LM741C offered intermediate results. The change of the IC is the only mod I have done. Quite easy...

A+!

[digthisbigcrux]

although, leds do sound pretty damned good.

[ode2no1]

you might consider putting the diodes on switches, one side being 914 or 4148 and the other being led's, that way you can have a rat, turbo rat, and a hybrid (which is how my turbo rat is set up) with one led and one stock diode. the ruetz mod is awesome too for a rounder, yet less distorted, rat tone.

[El Heisenberg]

The GGG biasing of the 2n5457 makes a difference too.

I bought an IC that NTE had listes as a replacement for the LM308. I have one that is stock with LM308, and one with the NTE IC and the GGG jfet bias mod.

They both sound the same. The NTE one is smoother, less harsh, but not much.

[El Heisenberg]

Wouldnt a real easy mod be to just stack another identical IC on top of the IC?? Like if u uswd an lm308 stick another on top!

[mremic01]

http://www.diystompboxes.com/pedals/PCRAT1.GIF

So it looks like R.G. Keen traced the schematic and it's been revised by both Jack Orman and Brad Fajardo. But Orman and Fajardo's revisions are inconsistent with the component values. I think for now I'll socket the ones that are different, but does anyone know what is going on here? Is there a definitive RAT and RAT2 schematic?

[El Heisenberg]

Dood the only difference besides clipping diodes (which should be easy to imagine How theyll effect the sound), the only diff between the Rat circuits (besides IC and tranny) are the biasing resistors for the JFET and IC. They can be 100k-2MEG. Ive seen all sortsa values in these two spots.

The difference in sound is MINIMAL. Not noticable.

Use 1 meg resistors. If u want use the 10k/22k voltage divider at GGG for the JFET.

[tubelectron]

Hi,

Some pics of my Vintage RAT RI returned to the original 1981 Rev. B specs :






As you can see, if you buy the unit for an affordable price, the transformation to an original RAT is easy to do...

A+!

[trjones1]

The GGG biasing of the 2n5457 makes a difference too.

I just noticed this difference between the GGG and Tonepad.  What is the difference in sound, if any?