Pro Co FATRAT

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Pro Co FATRAT

Postby ggbb » 13 May 2016, 16:17

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.

Image

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Re: Pro Co FATRAT

Postby Cub » 15 Jun 2018, 15:33

Little bump here. Has anybody seen a Fatso in the wild yet?
I wish I were a chestnut tree, nourished by the sun.
With twigs and leaves and branches and conkers by the ton.

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Re: Pro Co FATRAT

Postby Ichabod_Crane » 16 Jun 2018, 14:38

Hello, I don't know if someone knows the real schematic, but I can assume it, though I didn't try the original Fat Rat.
We can see the description here: https://www.ratdistortion.com/product/107/fat-rat
The pedal has two extra switch: the clipping switch Mosfet/Stock and the Fat switch: Stock/Fat.

- Look at the image attached. You can see how you can add the extra clipping mode using a DPDT switch.
- About the fat mode we can assume that it could be the Ruetz Mod, but if you want to use just a switch instead a pot you have to use a DPDT switch to select the stock resistor or a 1k resistor.
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Re: Pro Co FATRAT

Postby thesmokingman » 18 Jun 2018, 14:33

my notes show the fat switch to add a 6u8 to C7 and the MOSFET clipping to be bs170+1n270 pairs

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Re: Pro Co FATRAT

Postby p.eat » 25 Jun 2018, 11:20

thesmokingman wrote:my notes show the fat switch to add a 6u8 to C7 and the MOSFET clipping to be bs170+1n270 pairs

I can confirm. Fat switch adds 6u8 in parallel to C7. The Fat Rat I had used a BS170 and a BATxx for the Mosfet-clipping. The rest was to standard wf specs. My personal opinion: I found both switches rather useless....

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Re: Pro Co FATRAT

Postby brownwhopping » 23 Oct 2018, 19:48

p.eat wrote:
thesmokingman wrote: I found both switches rather useless....

Why? I used to make Rat with 3-way clipping switch (GE, SI and LED) and it sound very similiar. Is it this?
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Re: Pro Co FATRAT

Postby ggbb » 28 Dec 2018, 17:21

Thanks guys. Can anyone confirm the wiring of the FAT switch and cap? Does the switch connect and disconnect the cap at the R6-C7 junction or at ground?

Also - the configuration of the mosfet+diode clipper pairs - there are several ways to do it - can anyone confirm?
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Re: Pro Co FATRAT

Postby ggbb » 28 Dec 2018, 17:35

And if you could post gut shots that would be fantastic.
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Re: Pro Co FATRAT

Postby p.eat » 01 Jan 2019, 12:05

ggbb wrote:Thanks guys. Can anyone confirm the wiring of the FAT switch and cap? Does the switch connect and disconnect the cap at the R6-C7 junction or at ground?

Also - the configuration of the mosfet+diode clipper pairs - there are several ways to do it - can anyone confirm?


The switch makes/breaks the ground connection of the cap. It also adds a 2n2 cap from gate to ground on Q1 (the output buffer).
Clipping configuration is:
BATxx: anode to ground
BS170: drain to ground, gate and source connected.
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Re: Pro Co FATRAT

Postby ggbb » 01 Jan 2019, 21:38

p.eat wrote:The switch makes/breaks the ground connection of the cap. It also adds a 2n2 cap from gate to ground on Q1 (the output buffer).
Clipping configuration is:
BATxx: anode to ground
BS170: drain to ground, gate and source connected.


Thanks again - and for the pics you PM'd me.

Based on the pics, they have added 1 MOSFET, 1 diode, 1 film cap, 1 electro cap, and 1 resistor - plus 2 DPDT switches.

I am not sure about the added resistor. There are 12 in total, whereas the original white face RAT had 11. It is possible that the extra resistor may simply be an input pull-down which were not used in all original non-LED RATs, but the extra resistor labelled R12 is 1.6k - which makes the pull-down idea seem unlikely.

I can make out the resistor values from the pics for all except two - which are the dark blue sausage-style 1% resistors labelled as R5 and R8 on the FATRAT PCB. If those labels correspond to the Multi-RAT diagram, then they should both be 1k. I sill need confirmation there.

Most puzzling is that some values do not match up with the white face circuit. R1 and R6 appear to both be 5.6k, but should be 47. All other resistors match up. R1 doesn't really matter that much (and at least one RAT has been reported to have a different value there - 100 - the soulsonic RAT2 trace), but R6 matters a lot. Could I be reading those wrong - green-blue-black-silver-brown? Or could they be mis-marked? Or could your RAT have been mis-assembled (wouldn't be a first)? Confirmation by measurement would be helpful.

The DPDT MOSFET switch appears to have three wire connections on a single pole (so one pole is unused) and from your description above it sounds like the wiring for that is as below. Can you confirm?

Image

The FAT switch circuit is still a bit of a puzzle. I can't see the switch connections in the pics, but it appears to have three wires and uses both poles. It could be simply:

Image

However, the instruction manual states "it also increases gain" which suggests that it changes resistance, but it's difficult to be sure about that - they may simply mean bass boost. Full quote below.

Pro Co Sound wrote:Switching to the "FAT" setting gives you a treble roll off as well as a boost to the low end. Since it also increases the gain, it is most noticeable on low and mid gain settings.


I wonder if the resistor changes are part of the FAT circuit. If anyone has a FATRAT I would truly appreciate some feedback or a trace of the circuit.

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Re: Pro Co FATRAT

Postby p.eat » 03 Jan 2019, 21:01

The added resistor R12 is the clr for the led. ;-)

Here are the part values from my notes. Part numbering matches your schematic except C5 and C7 are swapped.

Code: Select all
resistors:
----------
R1 - 47R 1%
R2 - 100k 1%
R3 - 100k 1%
R4 - 1M 1%
R5 - 1k
R6 - 47R 1%
R7 - 560R 5%
R8 - 1k
R9 - 1k6 5%
R10 - 1M 1%
R11 - 10k 1%
R12 - 1k6 5%

capacitors:
----------
C1 - 100µ 25V
C2 - 1µ 50v
C3 - 22n
C4 - 1n
C5 - 2µ2 50V
C6 - 4µ7 35V
C7 - 100p mlc
C8 - 30p mlc
C9 - 4µ7 35V
C10 - 10n mlc
C11 - 3n3
C12 - 22n
C13 - 1µ 50V
C14 - 6µ8 50V
C15 - 2n2

other:
----------
Q1 - J310
Q2 - BS170
D1 - 1N4001
D2 - 1N4841
D3 - 1N4841
D4 - BATxx
U1 - OP07DP TI
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Re: Pro Co FATRAT

Postby ggbb » 03 Jan 2019, 22:43

p.eat wrote:The added resistor R12 is the clr for the led. ;-)

Here are the part values from my notes. Part numbering matches your schematic except C5 and C7 are swapped.


Ah yes - the CLR! Completely forgot about that. Thanks.

Where do these notes come from? A trace? Other source? The 47 ohm R1 and R6 resistors do not match up with the 5.6ohm markings in the pics, but of course 47 is the right value. :) Are the pics from your unit and if so did you measure those resistors? I hope you can forgive the scrutiny - being precise and accurate is important for me, and knowing the source of information is part of that.

Also - in the pics it appears that the electrolytic cap C5 is bipolar - can you confirm that? I see "BP" printed on one side and a I do not see any polarity marking but it's a bit difficult to see.
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Re: Pro Co FATRAT

Postby ggbb » 03 Jan 2019, 22:50

Also - so D4 is a BATxx schottky not 1N270 germanium. Any idea which BATxx? There are notable differences in Vf within the BAT4x family.
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Re: Pro Co FATRAT

Postby p.eat » 06 Jan 2019, 15:35

Unfortunately I don't have the unit anymore. I'm sure I determined the resitor values via the color band.
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Re: Pro Co FATRAT

Postby ggbb » 06 Jan 2019, 19:54

The green-blue-black-silver-brown markings on R1 and R6 in the pics are unmistakable - 5.6ohm (5.6k in my earlier post was a typo). Are those your own pics of the unit you had? Unless that unit had been modded (which seems unlikely given the values), I'd have to assume those are either a manufacturing mistake in that unit, or 47ohm resistors that are incorrectly marked. I've seen the former problem first-hand in a Vintage RAT I once owned. Obviously 47 is the correct value so it doesn't really matter that much other than it being quite a puzzle as to how that unit came to be as it is in the pics. I think the mosfet clipping and fat circuit are most likely as described earlier - All I need now is for someone with a unit to confirm the switching configurations for each feature and also the diode value. I expect the diode could be either CDSH270 or BAT41 as both have been used by Pro Co in other RATs. I'm also still curious about that bipolar electrolytic.
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