Pro Co FATRAT  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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Cub
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Post by Cub »

Thanks for that thorough review ! It's very interesting to read what somebody who knows the Rat circuit and sound so well thinks of these switches. Seems like it's not worth the effort for me to try and add these options to a build then, as I really like the classic stock sound already.

It took some digging, but I found your Bass Boost mod. Very clever ! Is it still either 180r + 15µF or 120r + 22µF. Or has your recipe changed over the years ?
Nearly all my attempts at mods to the RC filters with switches or Ruetz-ish (trim)pots just turned it from a Rat into something that isn't a Rat and not in a good way. Since your BB mod leaves the corner frequency intact, it's definitely something I'm going to try.

One mod to that section that I do like is based on our forum brother Moonwatcher's recipe of 49r + 2.3µF for the other RC filter. It lowers the corner frequency from the stock 1539 Hz to 1412 Hz.
Vintage/Whiteface Rat vs Modern Rat circuit question
The only difference is that I used a 51r resistor with the stock value of 2.2µF for the cap (1419 Hz). It's subtle and hard to put into writing, but it sort of goes from the stock "what a classic Rat ought to sound like" to "slightly more of what a classic Rat ought to sound like" if that makes any sense at all. It "ups the Rattiness" so to speak.

Love the increased volume and touch sensitivity of the LEDs in the Turbo. But when turning the gain up, I do miss some of that the fuzzy goodness from the classic pair of antiparallel 1N4148 diodes. I'll be experimenting with hybrid combinations for my next build and the best two or three options will go on a switch.
The Jam Pedals Rattler has a 1N4148 and a red LED in series on one side and a single 1N4148 on the other, the same recipe as the Asymmetric mode on the clipper switch for the Rat section of the EarthQuaker Devices Sunn O))) Life Pedal.
The Burn mode always was my favourite one on the Proco Solo, with two 1N4148 diodes series on one side and one red LED on the other. Two options for the same three components, It'll be fun to hear how they compare.
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ggbb
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BSIAB2/Pinnacle Hybrid
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Bluesbreaker
Notorious OD (Modified Bluesbreaker)
Timmy
Boss CS-2 Compressor
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Post by ggbb »

Cub wrote: 05 Feb 2023, 12:49 It took some digging, but I found your Bass Boost mod. Very clever ! Is it still either 180r + 15µF or 120r + 22µF. Or has your recipe changed over the years ?
Those values would be a bit extreme IMO. I don't know whether that's something I suggested for max effect at some point in time or is someone else's take on the mod. I've pretty much stuck with my original design which you can find here (not my blog): https://marcuseffects.wordpress.com/201 ... -bass-mod/. The original image source for the RAT BB mod is no longer online - it moved to https://www.diyschematics.com/schematic ... sBoost.gif

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Post by Cub »

Oh, I see. The values I found were for making it a permanent mod instead of making the sounds switchable.
https://www.diystompboxes.com/smfforum/ ... msg1062115

Good to have the values know safely stored in a folder and I can't thank you enough for sharing so much information over the years about the many different versions of the ProCo dirtboxes. They are some of my absolute favourite pedals in de world.
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Post by thesmokingman »

ggbb wrote: 01 Feb 2023, 23:46 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. This confirms p.eat's report but note the output JFET is a J109 in my unit. D4 is BAT41. Also worth noting is that the PCB layout is essentially a modified version of the original big box "filter" RAT PCB which was also used by original small box RATs as well as the Vintage and Whiteface reissues.

https://www.mediafire.com/view/4pdvsczb ... T.png/file

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so no pcb pictures then?

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Post by Beedoola »

I have a FatRat and the fat cap is not a 6.8uf but a 1uf. Are folks sure the schematic is correct? I built a clone using the layout from tagboardeffects and it doesn't sound anything like my stock Fatrat.

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ggbb
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BSIAB2/Pinnacle Hybrid
Cardinal Tremolo
Bluesbreaker
Notorious OD (Modified Bluesbreaker)
Timmy
Boss CS-2 Compressor
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Post by ggbb »

Beedoola wrote: 29 Jul 2023, 02:10 I have a FatRat and the fat cap is not a 6.8uf but a 1uf. Are folks sure the schematic is correct? I built a clone using the layout from tagboardeffects and it doesn't sound anything like my stock Fatrat.
It's not uncommon to have a RAT with non-standard values, as it seems they will occasionally use whatever they have handy in order to keep production moving. They also have assembly mistakes from time to time. A friend of mine had a Vintage RAT Reissue that contained BAT41 diodes for clippers and had swapped C7 and C8. I'm sure the FATRAT schematic is correct to my own unit and one other reported trace. The fact that the two agree with each other is strong evidence.

Are you sure your FATRAT is stock? Did you buy it new? Post photos of the PCB please. And a link the clone you built as well thanks.

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Post by Beedoola »

It was actually dirtboxlayouts. Here is the link to the layout. I noticed from tracing my FR that the distortion control locations are swapped. Here are some pics of my stock FR - I got it new online.

EDIT* It looks like R8 and C9 were reversed on the layout I attached. I swapped them and it sounds better. Let me know if anything else looks off on the layout.

Image
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ggbb
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Completed builds: Monte Allums Boss CS-3 Opto-Plus Mod
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Modified Fuzz Face
Orange Smoothie Compressor
OCR (Modified RAT)
BSIAB2/Pinnacle Hybrid
Cardinal Tremolo
Bluesbreaker
Notorious OD (Modified Bluesbreaker)
Timmy
Boss CS-2 Compressor
Scarab Deluxe
Mini Copy Chorus (Modified Small Clone)
PAiA Gator
Hot Cake
ODR-1
Mostortion
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Post by ggbb »

Beedoola wrote: 29 Jul 2023, 04:09 EDIT* It looks like R8 and C9 were reversed on the layout I attached. I swapped them and it sounds better. Let me know if anything else looks off on the layout.
That shouldn't make any difference. Maybe in correcting this you fixed a bad solder joint or something?

Note: I spotted a drawing error on Rev. J of the Multi-RAT schematic. Corrected version Rev. K is below.

https://www.mediafire.com/view/4pdvsczb ... T.png/file
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Post by Beedoola »

Thanks for the update.

That previous and per the FR layout that the filter 1 was going in series into the resistor and then cap and not the other way around would make no difference?

Also, I see the revision you made: thank you!

Having said that, it looks like SW2 for the clipping is to go to ground, right? In the FR layout it is not.

Also, in the layout the BS170 drain and BAT41 cathode are going to ground but that doesn’t look like that is what you have on the schematic.

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ggbb
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Completed builds: Monte Allums Boss CS-3 Opto-Plus Mod
Run-Off-Groove Improved EA Tremolo (modified)
Modified Fuzz Face
Orange Smoothie Compressor
OCR (Modified RAT)
BSIAB2/Pinnacle Hybrid
Cardinal Tremolo
Bluesbreaker
Notorious OD (Modified Bluesbreaker)
Timmy
Boss CS-2 Compressor
Scarab Deluxe
Mini Copy Chorus (Modified Small Clone)
PAiA Gator
Hot Cake
ODR-1
Mostortion
OCD v2
Straight Up Clean Boost/Cut
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Post by ggbb »

Beedoola wrote: 29 Jul 2023, 14:54 Thanks for the update.

That previous and per the FR layout that the filter 1 was going in series into the resistor and then cap and not the other way around would make no difference?

Also, I see the revision you made: thank you!

Having said that, it looks like SW2 for the clipping is to go to ground, right? In the FR layout it is not.

Also, in the layout the BS170 drain and BAT41 cathode are going to ground but that doesn’t look like that is what you have on the schematic.
My schematic is based on the actual FAT RAT that I own - there isn't anything more accurate than that (mistakes not included). Any layout - including the one from dirtboxlayouts - is an interpretation of a schematic or of another layout, possibly with added mods. Unless you know exactly the original source(s) for the layout and the details of any modifications, it should not be treated as accurate. This is part of the reason why I list my sources on the schematic. Just because it's on the internet doesn't mean it's "right". And let's be honest - most of the DIY pedal community contributions are copies - not original works at all other than perhaps a different layout or redrawn schematic.

Layouts often include accommodations to make the design or build simpler or easier. For example the different switching setup implemented by dirtboxlayouts - placing the clipping switch between the clippers and the circuit rather than the original switch between the clippers and ground. Usually these make no electrical difference to the functioning of the circuit. The order of R8 and C9, as used in this case should not make any difference electrically or sonically. I think the reason for this deviation from the original circuit is that many RAT schematics available on the internet including some that are very often cited contain this "error". All of the RATs that I've owned have R8 first, but I haven't owned every RAT variation ever produced. It's possible that the bud box RAT prototype had C9 first - I have no way of knowing that - which may explain the source of this "error" (but I doubt this is true).

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ggbb
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Joined: 12 Jan 2011, 22:16
Completed builds: Monte Allums Boss CS-3 Opto-Plus Mod
Run-Off-Groove Improved EA Tremolo (modified)
Modified Fuzz Face
Orange Smoothie Compressor
OCR (Modified RAT)
BSIAB2/Pinnacle Hybrid
Cardinal Tremolo
Bluesbreaker
Notorious OD (Modified Bluesbreaker)
Timmy
Boss CS-2 Compressor
Scarab Deluxe
Mini Copy Chorus (Modified Small Clone)
PAiA Gator
Hot Cake
ODR-1
Mostortion
OCD v2
Straight Up Clean Boost/Cut
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Post by ggbb »

thesmokingman wrote: 18 Mar 2023, 14:38 so no pcb pictures then?
Better late than never :) .
Attachments
IMG_0544.JPG
IMG_0543.JPG
IMG_0541.JPG

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