It's fairly well known that EMG preamps are designed to work with as much as 27 volts. The 18 volt modification is pretty common among bass players, as it offers more dynamic range and greater headroom, reducing the amount of built-in compression that the EMG preamp performs in 9 volt operation. However, on EMG's own advice
, there's not much benefit of 27 volts over 18, so i'll focus on the 18 volt mod here.
There are a few scattered threads on the forum asking about the 18v mod, so i thought i'd do one comprehensive writeup incorporating everyone's input on how to do the 18v mod. Of course, you can do this by modifying the guitar's original wiring, but when i saw this idea, i thought it was pretty clever, and 100% reversible without changing your guitar's original wiring. (Making it really easy to switch back if you prefer 9 volt operation of your EMGs.)
The idea is to bump the voltage feeding the EMG preamp to 18 volts in order to increase dynamic headroom. You can run two 9 volt batteries in parallel to double battery life, but that's not the point of this exercise.
All you need is a soldering iron, some electrical tape and/or heat shrink tubing and three 9 volt battery clips from Radio Shack (or somewhere similar).
And, since a picture is worth a thousand words, i'll save you from any further reading by providing a handy diagram which explains it all:
It's also been asked a number of times if the 18 volt mod will benefit other active pickups or preamps. The best advice is to consult the preamp's manufacturer. I believe Bartolini preamps do well with 18 volts. However, Seymour Duncan Blackouts have a preamp that's designed to offer optimum headroom at 9 volts, making the 18 volt mod unnecessary.
DISCLAIMER: All modifications, including this one, are undertaken at your own risk. If you screw something up and you blow up your guitar, your pickups/electronics, your cables, your pedals, your amp or yourself, it's your own damn fault. You will not hold the author of this post or sevenstring.org liable for any personal injury or loss or damage of personal property that may arise from this modification.