This is a custom Rat, built as a gift for my friend/bandmate. It's close to a Fat Rat, but the clipping switch implements "turbo" (LEDs) instead of the MOSFET scheme of the actual Fat Rat. My buddy is fairly new to guitar, yet already showing signs of GAS. I haven't yet sold him on DIY gear, but my efforts are young. His pedal journey is in its infancy, and he recently acquired a TC Electronic Magus Pro, which is purportedly a ProCo Rat clone. He loves it!
The Magus Pro has a single three-way toggle, where one mode is standard Rat, one is "fat" mode, and one is "turbo". I wasn't able to find any traces of the Magus Pro, so I'm not really sure how they implemented the "fat" setting. The Rat is of course a long-lived, and ever-popular pedal, whose circuit is well-known. There are numerous mods in general, and many in particular for adding bass. The "Ruetz mod" is probably the most famous bass mod; that is essentially a Timmy-style bass control that allows for a variable amount of bass cut, rather than the stock fixed cut (which is rather aggressive, and results in a very strong mid emphasis). According to this Multi-RAT Schematic, the actual ProCo Fat Rat uses a different scheme to implement the "fat" setting, i.e. to add more bass.
While I couldn't find a schematic of the Magus Pro, there are images of the guts, and that single switch looks too small to actually implement the "fat" mode the same way the actual ProCo Fat Rat does it. So, I knew from the start I probably couldn't clone the Magus Pro exactly, and mentally went back and forth between giving him a Reutz knob, or a fat switch. I ended up going with the fat switch, as I'm a big fan of the Barber-style "three knobs and two switches" scheme. I actually briefly owned a ProCo Fat Rat many years ago, before I started building pedals. Besides being obnoxiously large, it has a clipping select toggle, which allows choosing between standard and "mosfet" clipping. I personally remember the mosfet clipping setting to be minimally different from standard clipping. And back in the day, I also had a Mooer Black Secret, another Rat clone - but it had a "turbo" switch, which uses LED clippers instead of the standard 1n914/1n4148. That I found to be noticeably different, and a generally useful setting. So I preserved it here.
The other small variation I made was to replace the output buffer JFET with an NPN BJT. My thinking was, particularly for a buffer (following a heavily deliberately distorted signal), JFET vs BJT performance is negligible. But BJTs are generally dramatically easier to work with. This to me seems like a no-brainer modernization of the Rat circuit. Rat purists may of course scoff, but... I'm also using an OP07! Oh, the horror!
Lastly, the bottom half of the PCB is my now-standard always-active input and output buffers, along with microcontroller-based electrical bypass switching.
The build was unremarkable. Or, this build I should say; this is actually the second build. On my first PCB, I made a couple mistakes that required a PCB revision. Now it's all sorted. It worked great at first power-on. Hopefully I'll be able to deliver it to my friend this weekend.
The Magus Pro has a single three-way toggle, where one mode is standard Rat, one is "fat" mode, and one is "turbo". I wasn't able to find any traces of the Magus Pro, so I'm not really sure how they implemented the "fat" setting. The Rat is of course a long-lived, and ever-popular pedal, whose circuit is well-known. There are numerous mods in general, and many in particular for adding bass. The "Ruetz mod" is probably the most famous bass mod; that is essentially a Timmy-style bass control that allows for a variable amount of bass cut, rather than the stock fixed cut (which is rather aggressive, and results in a very strong mid emphasis). According to this Multi-RAT Schematic, the actual ProCo Fat Rat uses a different scheme to implement the "fat" setting, i.e. to add more bass.
While I couldn't find a schematic of the Magus Pro, there are images of the guts, and that single switch looks too small to actually implement the "fat" mode the same way the actual ProCo Fat Rat does it. So, I knew from the start I probably couldn't clone the Magus Pro exactly, and mentally went back and forth between giving him a Reutz knob, or a fat switch. I ended up going with the fat switch, as I'm a big fan of the Barber-style "three knobs and two switches" scheme. I actually briefly owned a ProCo Fat Rat many years ago, before I started building pedals. Besides being obnoxiously large, it has a clipping select toggle, which allows choosing between standard and "mosfet" clipping. I personally remember the mosfet clipping setting to be minimally different from standard clipping. And back in the day, I also had a Mooer Black Secret, another Rat clone - but it had a "turbo" switch, which uses LED clippers instead of the standard 1n914/1n4148. That I found to be noticeably different, and a generally useful setting. So I preserved it here.
The other small variation I made was to replace the output buffer JFET with an NPN BJT. My thinking was, particularly for a buffer (following a heavily deliberately distorted signal), JFET vs BJT performance is negligible. But BJTs are generally dramatically easier to work with. This to me seems like a no-brainer modernization of the Rat circuit. Rat purists may of course scoff, but... I'm also using an OP07! Oh, the horror!
Lastly, the bottom half of the PCB is my now-standard always-active input and output buffers, along with microcontroller-based electrical bypass switching.
The build was unremarkable. Or, this build I should say; this is actually the second build. On my first PCB, I made a couple mistakes that required a PCB revision. Now it's all sorted. It worked great at first power-on. Hopefully I'll be able to deliver it to my friend this weekend.
