Converting current production RAT 2 into a Turbo Rat - just swap two diodes?

[scorchedcortex]

Hello folks,

Just curious - can I convert the current chinese production PROCO RAT 2 into a Turbo RAT just by replacing the two clipping diodes (D2 and D3) with LEDS (like the Turbo uses)?

From my understanding the LEDS are the only difference between the two.

Anyone try this? If so, does it make it sound like the Turbo?

Thanks!

[aron]

If that's the only difference then yes. Good first mod.

[idy]

A thread entry that covers all the details:
https://www.aronnelson.com/gallery/main.php/v/diyuser/GGBB/Multi-RAT.png.html

The LEDs seem the major difference. There is a bigger cap in one spot, a different biasing arangement on the fet, an extra resistor to ground near the output.

But these things may have very little effect on the sound. I would try just changing the diodes to LEDs.

[scorchedcortex]

Excellent! Thank you.

Quick question - unity gain on my rat is around 3 o'clock on the volume knob. Is that typical for RAT pedals?

Is there a mod to boost output?

Thanks for the help!

[willienillie]

It will might be louder with LED clippers.

[bloxstompboxes]

Check out the schematic in the second post in this thread. Made by a local forumite and quite complete.

https://www.diystompboxes.com/smfforum/index.php?topic=113907.20

EDIT: oops. second post in the thread. lol.

[mwelch55]

On my latest RAT build, I installed a 12 position rotary switch for clipping options.  I have every kind of clipping I could think of.  One of my favorite diodes to use for clipping is the Russian D9E.  Red LEDs and Clear LEDs also sound great.

The nice thing about the 12 position switch is that I can get a pretty good comparison of the different clipping configurations.

Mike

[287m]

Check out the schematic in the first post in this thread. Made by a local forumite and quite complete.

https://www.diystompboxes.com/smfforum/index.php?topic=113907.20

aha, you read my mind, just draw mini layout for friend. And always forget lug numbering, always. Hope Gord update that schemo.

[GGBB]

a different biasing arangement on the fet

This can affect the sound depending on the JFET. It's just a matter of where in the spec range for Vgs-off the particular JFET in the pedal happens to be. It's important to note that the JFET biasing change was made specifically for the Turbo RAT. The theory is that the greater output level allowed by the LED clippers vs silicon has a greater likelihood of pushing the JFET into cutoff with the original biasing scheme (to 0V), so the bias point was shifted to 1/2V+ to move the JFET farther away from cutoff.

[GGBB]

Hope Gord update that schemo.

Rev. I is the latest Multi RAT schematic (https://www.aronnelson.com/gallery/main.php/v/diyuser/GGBB/Multi-RAT.png.html). I am working on a new revision with FAT RAT info, but have yet to verify the circuit 100% - I'll probably just have to break down and buy one.