RAT from Tonepad with some mods

[Soeren_DK]

Hi there great DIY friends.

I have bought the RAT board from Tonepad --> http://tonepad.com/getFile.asp?id=89
and thinking of doing some mod on it so I started doing some research before starting. Found that Keeley is doing the mod but I can't find any info about how to his mod.
Anybody know what the Keeley mod do?

I found this mod on http://www.beavisaudio.com/ --> http://www.beavisaudio.com/projects/FKR/images/MightierMouse.gif
Anybody tried overdrive mod?
As I can see I think the to wires from the switch should be soldered to 1 and 3 of the overdrive potmeter on the tonepad pcb.

Cheers
Soren

[richon]

RUETZ MOD is good.
test other materials on the coupling caps, like poly, tantalum.etc

test leds or mosfets as clippers...  and maybe asymetric.

[BAARON]

It sounds very good with your clipping diodes in the feedback loop instead of going to ground, which makes it a nice crunchy overdrive instead of distortion.  LEDs work well for the feedback loop clipping diodes.

[Soeren_DK]

It sounds very good with your clipping diodes in the feedback loop instead of going to ground, which makes it a nice crunchy overdrive instead of distortion.  LEDs work well for the feedback loop clipping diodes.

I'm can't figure this out. What diode?, The one I'm putting across the dist. pot or?

Cheers
Soren

[BAARON]

Here you go, with an "overdrive/distortion" clipping switch and everything to go between the two mods.  The diagram shows silicon diodes for the default clipping and LEDs for the overdrive clipping, but use whatever you want.

You don't HAVE to jumper lugs 2&3 on the gain pot, but it's a good idea.



Blue = wires.  Black = everything else.  This is specifically for the Tonepad RAT board.

[richon]

my RAT with 2n7000 mosfets as clippers sounds more versatile than with SI diodes.... 

[BAARON]

my RAT with 2n7000 mosfets as clippers sounds more versatile than with SI diodes.... 

How are yours wired, out of curiosity?  For the ~2v soft-knee clipping (gate junction clipping) with blocking diodes pointing in the proper direction on each MOSFET, or for the MOSFET body diode (basically just a silicon diode with high capacitance, which makes it darker) without any blocking diodes?  Or with blocking diodes, but pointing in the same direction as the body diodes (which basically just turns into a bunch of Si diodes)?  If you're not sure, you can check with your multimeter and see what the combined forward voltage is in each direction.  It should be >2v if they're arranged for soft-knee clipping, or <2v if they're just acting as silicon diodes.

Or do you have it set up a different way entirely?

[richon]

sorry, but my pedal is closed yet


they are wired antiparalel, just like they are used in the OCD pedal....  maybe this explains it to you.

[BAARON]

sorry, but my pedal is closed yet


they are wired antiparalel, just like they are used in the OCD pedal....  maybe this explains it to you.

It does!  The OCD uses the silicon body diodes of the MOSFETs, rather than the soft-knee clipping method.

[richon]

how does it change the way it acts as a "clipper"

[BAARON]

http://www.diystompboxes.com/smfforum/index.php?topic=76337.msg623609#msg623609

MOSFETs clip in both directions, and they do it differently.  In one direction, they're basically just silicon diodes with a high input capacitance (which cuts highs a little bit) and they clip at about 0.6-0.7 volts, and in the other direction they're a soft-clipping device that clips somewhere around 2 volts (give or take a bit, depending on the MOSFET).  In order to use the soft-clipping side, you need to set up diodes in series with them pointing in the opposite direction of the body diode (i.e., it will need to point toward the MOSFET's drain/away from source) to make sure that the body diode cannot conduct.  Otherwise, once the voltage reaches the forward voltage of the body diode it will clip, and it never reaches the forward voltage of the soft-clipping mode in order to clip in that direction.