Author Topic: Fat rat schematic  (Read 641 times)

jimilee

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Fat rat schematic
« on: November 07, 2021, 02:32:41 PM »
Does anyone happen to have a schematic for the fat rat? I’m specifically interested in the mosfet clipping part.


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Zerro

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Re: Fat rat schematic
« Reply #1 on: November 07, 2021, 05:01:29 PM »
One note about that mosfet part is here:
https://www.freestompboxes.org/viewtopic.php?t=27632

Another picture is attached:
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jimilee

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Re: Fat rat schematic
« Reply #2 on: November 07, 2021, 05:08:11 PM »
One note about that mosfet part is here:
https://www.freestompboxes.org/viewtopic.php?t=27632

Another picture is attached:
Thank you. I think I have a better understand if the implementation of the mosfet. What website is the picture from?


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Zerro

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Re: Fat rat schematic
« Reply #3 on: November 08, 2021, 08:07:40 AM »
"Nudíte se? Kupte si našeho cvičeného ježka! Pobaví vás svými veselýmí kousky!"

jimilee

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Re: Fat rat schematic
« Reply #4 on: November 08, 2021, 09:21:17 AM »
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Aentons

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Re: Fat rat schematic
« Reply #5 on: November 08, 2021, 02:22:09 PM »
If you are going all in on the Rat... Here is a a rathole for you to go down.

It's a disection of an LM108/208/308 opamp.

http://www.righto.com/2016/12/inside-lm108-op-amp-superbeta.html?m=1

Thing of note are:

at the bottom it talks about how each manufacturer had their own design and or implementation that could be factors in the sound

How they use special  "Super Beta" transistors to get a gain of 5000

jimilee

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Re: Fat rat schematic
« Reply #6 on: November 08, 2021, 02:51:19 PM »
If you are going all in on the Rat... Here is a a rathole for you to go down.

It's a disection of an LM108/208/308 opamp.

http://www.righto.com/2016/12/inside-lm108-op-amp-superbeta.html?m=1

Thing of note are:

at the bottom it talks about how each manufacturer had their own design and or implementation that could be factors in the sound

How they use special  "Super Beta" transistors to get a gain of 5000
Very cool, thank you.


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thesmokingman

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Re: Fat rat schematic
« Reply #7 on: November 08, 2021, 08:17:46 PM »
now the things my notes didn't say was whether it was wired as a mosfet or a mosfet body diode, which makes a considerable difference in Vf especially if using the BS170. wired as the body diode it puts the Vf around 1V and for hard clipping that's a pretty sweet spot ... wired as a mosfet you're going to end up with something closer to the turbo rat but with smoother clipping. either way is good and you can't go wrong ... fwiw I used an AMD LM108 in mine
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jimilee

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Re: Fat rat schematic
« Reply #8 on: November 09, 2021, 09:08:05 AM »
now the things my notes didn't say was whether it was wired as a mosfet or a mosfet body diode, which makes a considerable difference in Vf especially if using the BS170. wired as the body diode it puts the Vf around 1V and for hard clipping that's a pretty sweet spot ... wired as a mosfet you're going to end up with something closer to the turbo rat but with smoother clipping. either way is good and you can't go wrong ... fwiw I used an AMD LM108 in mine
I was thinking about wiring it up a couple of different ways. Like the turbo rat or I. The feedback loop like the roadkill / brat. I’m laying it out in eagle, I plan on using sockets to switch it in and out.


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Aentons

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Re: Fat rat schematic
« Reply #9 on: November 12, 2021, 02:51:36 PM »
Here is another Rat variant with an interesting OD / Dist switch. I have one of these and it sounds great on both settigs

Maxon OD-01 "The Driver"



« Last Edit: November 12, 2021, 03:11:23 PM by Aentons »

jimilee

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Re: Fat rat schematic
« Reply #10 on: November 12, 2021, 06:30:56 PM »
Very cool, thank you. I’m having a roadkill PCB made and then I found the solo, so that’s gonna be next.


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