The DOD 210 FET Preamp is a preamp pedal built around a field-effect transistor (FET) gain stage, the same kind of simple, touch-sensitive amplifying stage found in many boost and preamp designs. It sits in the family of preamp pedals that push a signal louder and fuller rather than heavily distorting it. The pedal appears to be on the rare side, so most players meet it through DIY reproductions rather than the original unit1.
What it does
The circuit is, in the words of the layout author at Guitar FX Layouts, a straightforward FET design: "The input is connected to the gate, via the 220K resistor. It looks like a classic FET gain stage to me."1 A FET gain stage responds to picking dynamics much like a tube preamp does, cleaning up when you play lighter and thickening up when you dig in.
As for what it sounds like, the layout author's expectation is that it "should have lots of boost on tap and fatten up your tone nicely"1. That places it in the same territory as boost pedals: volume and body first, grit as a byproduct of pushing the stage hard.
The DIY layout
Because original units are scarce, the circuit lives on mainly through a vero (stripboard) layout published on Guitar FX Layouts in July 20201. Stripboard is a perforated board hobbyists use to build pedals by hand, cutting traces and soldering components in rows.
A few practical points from the layout's development:
- The original layout had an error: Volume 2 should connect to the output. The author confirmed the correction and fixed the layout on 13 July 20201.
- The author recommends builders "insert at least a 47uF cap to filter power supply noise, and in case, a polarity protection diode"1.
- The layout has been verified with a J202 FET transistor, with the builder reporting "Crisp boost that gets dirty. And LOUD!"1
A J113 transistor has also been mentioned as a substitute in discussion of the layout, but the choice between J202 and J113 has not been settled, so builders may want to try both if they have them on hand.
Related circuits
The 210 is a rare pedal, and one builder who traced the circuit into a vero (stripboard) layout for stompbox use noted that it "seems to be on the rare side to boot"1. The same builder verified the layout with the J202 transistor, reporting a "crisp boost that gets dirty. And LOUD!"1.
Questions
What kind of transistor does the DOD 210 FET Preamp use?
The circuit is a classic FET gain stage, and builders have verified the layout with the J202 FET transistor. With a J202 installed, one builder described the result as a crisp boost that gets dirty and is very loud. A J113 substitute has also been mentioned by builders, though the two options have not been settled between.
Is the DOD 210 FET Preamp easy to find?
No. The pedal appears to be on the rare side, so most players who want the circuit today encounter it through DIY stripboard layouts rather than the original unit. Builders of the layout suggest adding a 47uF capacitor to filter power supply noise, and optionally a polarity protection diode.
Sources (1)
- Guitar FX Layouts: DOD 210 FET Preamp, Guitar FX Layouts (tagboardeffects.blogspot.com), 2022-07-09
