Another Filthy Rodent - Cloning the Old School Rat / Dirty Rat

The Pro Co Rat distortion pedal in one of the most ubiquitous effect pedals sold. It remains inexpensive in its base version (about $79 new), though modified pedals quickly climb over $100. For example, the germanium diode equipped "Dirty Rat" version retails for $179. With prices for the basic unit so low, it therefore only makes economic sense to clone one of the modified boutique variants of the Rat. Though cloning a basic pedal is always fun if you want to make your own unique looking version of the pedal. I've previously cloned the Rat using an AionFX Helios board. The AionFX board had multiple clipping diode options and the Ruetz mod (Sweep knob) built in on the front. Opinions vary on the efficacy of the Ruetz mod, but having multiple clipping options is always fun. For this build, I went with a different board that retains most of the functionality of the AionFX board, but in some ways is a bit more true to the original.

First introduced in 1978, the early Rat pedals were awash in fairly vintage components. Because of noise floor concerns, I decided to stick with film capacitors rather than ceramics (a mix of Panasonic, Topmay, and Apex) and carbon film (rather than carbon composition) resistors (5% 1/4W Yageo for the most part). The electrolytic capacitors are all brand new production Nichicon. The PCB is another one from South Obolon FX's Ukraine Support line, so I got the files to make these through a donation to Ukraine's ongoing defense. In some areas it can be hard to source the 2N5457 JFET, so alternate resistor / transistor options are provided (the unpopulated R8_A and Q1_A spots on the silkscreen) so a normal silicon NPN transistor could be used instead. I haven't tried that particular mod as I had a lot of JFETs I'd picked up from Pedalhacker, but I may in a future version.

I also had what I hope is a genuine LM308N op amp - it seems to be working properly - as I was really going for an "old school" inspired build on this one. That being said, I also have a supply of OP07 op amps I can pop in to compare the two. The board incorporates two of the most popular modifications of the Rat as well. Both were originally designed to be internal, but with a little back and forth with South Obolon FX, we found a way to move one of them external! The Ruetz mod changes the cutoff frequency for one of the op-amp stages' high-pass filter. I could have taken this external with a trim pot, but decided to leave it internal. The other mod is the choice of clipping diodes. The board includes space for the original Pro Co Rat silicon diodes (1N914) as well as the Dirty Rat's germanium diodes (1N34A). You could hypothetically also make the Turbo Rat version with two Red LEDs - or mix and match. I decided to stick with the Rat / Dirty Rat combo.  

For the off board wiring, I decided to try something different on this build - I ran all of the power, ground, and connection wires from the bottom of the PCB rather than the top. These boards were originally laid out to where people could etch their own PCBs rather than having to get them fabricated, so almost all of them are effectively one sided to the bottom. This board was also originally designed to go into a 1590B enclosure with side mount jacks, but I wanted to transfer it over to a 125B with top mount jacks. That made the knob placement a little unusual, but it also gave me room to add a sub-miniature SPDT switch to the clipping control and bring it to the front of the unit. 

The enclosure features more dino art from Ukrainian artist Estelkatrin. This time around, it's the Ratchasimasaurus (a mouthful for sure, bit we've effectively got the Rat - asaurus). According to Wikipedia:

"Ratchasimasaurus (meaning "Nakhon Ratchasima lizard") is a genus of iguanodontian ornithopod dinosaur from Early Cretaceous (Aptian stage) Khok Kruat Formation of Nakhon Ratchasima Province in northeastern Thailand."

So, it's a fairly obscure dinosaur, but there were some interesting life interpretations online, and the artist was able to run with it. Since it is an Asian dinosaur, I sort of went with my Asian theme for the rest of the pedal art using licensed clipart. 

As to the pedal - well, it's a Rat. It sounds like a Rat and responds like a Rat. Because the Ruetz mod is internal, I just sort of set it where I like and leave it. I love having the option of going between the regular Rat and Dirty Rat modes at the flip of a switch. The AionFX pedal has a clipping switch, but  his interpretation of the clipping stage and its functionality is a bit different, and if I'm being honest I kind of like the raw, basic Rat sound of this one better.