Pro Co FATRAT

[GGBB]

Does anyone know what Pro Co has done to the RAT to make it a FATRAT? I'm talking actual circuit and/or component changes not sound/features. If anyone has any gut shots or an actual verified/traced schematic that would be great. I'd like to update my comparative multi RAT schematic (below) to include this new RAT variation so I'm really curious as to what they've done.

[bloxstompboxes]

I don't have an answer for you but I do appreciate that schematic above and have used it for my own multi-rat board design.

[vigilante397]

I don't have a schematic or specific values, but if I understand correctly they added a "Fat" switch, which I assume is a tone cap selector, and they have a clipping switch that switches between the original silicon diodes and MOSFETs for clipping.

EDIT: Just peeked at a thread on FSB and he says C6 is the one on the Fat switch, though I don't own one and have never seen guts so I can't confirm.

[GGBB]

I don't have a schematic or specific values, but if I understand correctly they added a "Fat" switch, which I assume is a tone cap selector, and they have a clipping switch that switches between the original silicon diodes and MOSFETs for clipping.

EDIT: Just peeked at a thread on FSB and he says C6 is the one on the Fat switch, though I don't own one and have never seen guts so I can't confirm.

Can you give me the link to that thread (PM if you wish)?

But without actual facts, we can only speculate. My own "fat" mod I call BB (bass boost) changes C6 but simultaneously lowers R7. Changing C6 alone doesn't do much. Also, in demos I've heard, the FAT mode sounds like it rolls off top end and that's what Pro Co says it does. So I suspect it's more than just C6. I'm also curious as to how they do the MOSFET clippers. Probably just like the OCD is my guess, but I wonder which OCD and where in the circuit they put them.

[GGBB]

Bumping this topic. On the other forum, a couple of people have chimed in that the FAT mode is a 6u8 added in parallel with C7 2u2. One also added that the MOSFET clipping is done with BS170 + 1N270 (no details exactly how).

So I'm looking for further confirmation and especially details about how its confirmed (e.g. actual unit traced by 1st party, your buddy told you, you read it on the web, ...).

Also how things are connected.

For that FAT mode, where and how is the cap switched? Make-break at R6-C7 junction or at ground?

For the MOSFET clipping:

• How are the MOSFETs wired (gate to drain or source?)
• How are the MOSFETs and diodes connected (diode to gate or source?)
• How are the diodes oriented (reverse of MOSFET body or same?)
• How is the switching implemented (regular diodes on or off via SPST or ...?)

[oliveblues]

Hello,

i have a trouble with FATRAT. I ve put an invert polarity 18 volt ac !
i found the resistor that dammage ! its R1 but can't find the value of the resistor to change it !
Could you help me ?

Thnak u so much !

Olivier

[ashcat_lt]

its R1 but can't find the value of the resistor to change it !

That resistor's value isn't super critical.  The 47Ohms shown in the schematic above is as a good a guess as any.  You're lucky it exploded before the  diode did, because with the diode gone, there's nothing stopping that reversed voltage from destroying everything else in the circuit that cares about polarity.

[oliveblues]

Thank you ! is the watt value important? i see in the schematics it was the same resistor in R6. i make a picture of R6.

[antonis]

is the watt value important?

Not particularly..
(with 10mA arbitrary total current consumption value, 47R resistor power dissipation is less than 5mW..)

[oliveblues]

Thank you soooooo much Guys !!! 

[ElectricDruid]

Thank you ! is the watt value important? i see in the schematics it was the same resistor in R6. i make a picture of R6.

Smaller is probably better, since if it had been a big chunky resistor, it wouldn't have burned out, and you'd have a properly fried board now. On that basis, I might go for a 1/4W or 1/8W resistor rather than the 0.6W metal films I usually use for everything. Regard it as sacrificial, and hope it provides a bit of protection.

As Antonis says, during normal operation almost anything will be fine.

[oliveblues]

Thank you Electric Druid

[iainpunk]

i recommend mounting it upright, so it has minimal contact with the pcb, so it doesn't get damaged. maybe even salvage the glass tube from a blown fuse to protect the rest of the pedal while this resistor lets out the magic smoke.

cheers, Iain

[oliveblues]

Thank you Iain ! 

[ashcat_lt]

Yeah, if you intend to keep using it as a fuse, then definitely use a smaller wattage.  I'd rather put a schottkey diode in that spot. 

[rankot]

Yeah, if you intend to keep using it as a fuse, then definitely use a smaller wattage.  I'd rather put a schottkey diode in that spot. 

It's much better to use Schottky diode in series with that resistor, and you can use 0.6W resistor in that case.

Having both is important for two reasons:
1. Resistor is probably part of a low pass filter with filter capacitor, thus removing it completely will stop filtering DC power.
2. Diode will disable current flow in case of wrong polarity, so resistor will not burn (nothing will burn, actually).

[ElectricDruid]

It's much better to use Schottky diode in series with that resistor, and you can use 0.6W resistor in that case.

Yes, I completely agree with Rankot - adding a Schottky diode (1N5817 or something similar, for example) in series with the resistor is a much better idea than using the resistor alone. It's a worthwhile upgrade and provides much more solid protection.

[GGBB]

Well, I finally bit the bullet and bought a FatRAT. Traced it and have added the details to my Multi-RAT schematic. The FAT switch mod is kind of interesting.

https://www.mediafire.com/view/4pdvsczbyvlusgx/Multi-RAT.png/file

[antonis]

finally

Not so much as 7 years, Gord..

[ElectricDruid]

It's still an incredible bit of work, Gord.