# Differences Between Rat and Turbo Rat



## A2K (Aug 3, 2021)

I'm interested in building a turbo rat. Are there any differences from the classic rat besides the led clipping diodes? If so, what would I need to modify on the Muroidea pcb to make it a turbo rat?

Thanks!


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## Mcknib (Aug 3, 2021)

There's some info here 

Turbo rat vero notes


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## A2K (Aug 3, 2021)

Mcknib said:


> There's some info here
> 
> Turbo rat vero notes


Thanks for the link. The first post says it's the same except with 5 mm LEDs, a 2M2 gate resistor, and another 2M2 resistor between Gate and Drain. But then the second post says thr only change is the LEDs. So it's still not really clear to me.

If a Turbo is just a regular with 5 mm LEDs, then I guess I'd just do the old 3 way diode switch mod and have both options available.


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## Mcknib (Aug 3, 2021)

A2K said:


> Thanks for the link. The first post says it's the same except with 5 mm LEDs, a 2M2 gate resistor, and another 2M2 resistor between Gate and Drain. But then the second post says thr only change is the LEDs. So it's still not really clear to me.
> 
> If a Turbo is just a regular with 5 mm LEDs, then I guess I'd just do the old 3 way diode switch mod and have both options available.


As far as I know it is just the LEDs that are the difference I had one a while ago and that's all I could see but I didn't examine it in any great detail

Basically got it off eBay for parts not working and loaned it to a guy


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## thesmokingman (Aug 3, 2021)

There's a multi-rat schematic floating around that will give you all the combinations and differences
http://guitar-fx-layouts.42897.x6.nabble.com/file/n45577/Multi-RAT.png
I don't recall there being a more up-to-date version of that document with any of the newer Rat models available


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## A2K (Aug 3, 2021)

thesmokingman said:


> There's a multi-rat schematic floating around that will give you all the combinations and differences
> http://guitar-fx-layouts.42897.x6.nabble.com/file/n45577/Multi-RAT.png
> I don't recall there being a more up-to-date version of that document with any of the newer Rat models available


This is great,  thank you for posting!


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## A2K (Aug 3, 2021)

thesmokingman said:


> There's a multi-rat schematic floating around that will give you all the combinations and differences
> http://guitar-fx-layouts.42897.x6.nabble.com/file/n45577/Multi-RAT.png
> I don't recall there being a more up-to-date version of that document with any of the newer Rat models available


So comparing to the original circuit, it looks like straight value substitutions to get to a TR except for adding:

1) the 10k resistor between C10 on the Muroidea PCB (C13 on the multi-rat schematic) and the pin 3 of the Volume pot and 
2) the 2M2 resistor near the 2N5458 (R16 on the multi-rat schematic) - maybe the 2M2 resistor between Gate and Drain mentioned in the vero notes posted earlier? Sorry for the noob question. 

How would I add these resistors to the Muroidea PCB? Would they even make any difference to the pedal's sound?


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## manfesto (Aug 4, 2021)

A2K said:


> So comparing to the original circuit, it looks like straight value substitutions to get to a TR except for adding:
> 
> 1) the 10k resistor between C10 on the Muroidea PCB (C13 on the multi-rat schematic) and the pin 3 of the Volume pot and
> 2) the 2M2 resistor near the 2N5458 (R16 on the multi-rat schematic) - maybe the 2M2 resistor between Gate and Drain mentioned in the vero notes posted earlier? Sorry for the noob question.
> ...


Basically, no, it won’t change how the circuit sounds.

The 2N5458 is just an output buffer stage, you should check out this AMZ article on buffers






						Basic Buffers
					

Basic buffer circuits for use with guitar effects pedals.




					www.muzique.com
				




On the Muroidea (and most versions of the Rat circuit), the 1M gate resistor sets the input impedance at 1M.

If you change that to 2M2 and hook another 2M2 between the gate and drain, the input impedance is set to 2M2 || 2M2, or basically the same 1M.

Really the only thing that makes the turbo Rat different is the LED clipping (and that is *more* than enough)


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## Feral Feline (Aug 4, 2021)

The core Rat circuit is basically unchanged since inception and it's been around a long time, so...
- There's a lot of info online about the Rat;
- Lotsnlots of mods. 

The MultiRat schematic was compiled by G Tranter, who also has a great trio of bass mods for the Rat. If you play bass I highly recommend checking them out. I chose his 2nd one for my build, and used a DPDT switch to have stock, Turbo and Fat clipping options. Turbo is my favourite mode.

It should be noted there are many revisions of the MultiRat schematic, I think the Rev I posted above is the latest greatest. I had Rev H, so thanks for posting the links, Mcknib and thesmokingman.


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