[darren]

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.

[yellowv]

This has been posted before, but your diagram is better.

[darren]

Yes, i know it's been posted before, but the information is really scattered across a few disparate threads that are hard to search for because "EMG" and "18v mod" all fall below the forum's search threshold.

And my diagram is better.

I've done a quick A/B test with the EMG 808 in my Agile Intrepid Pro. I played something really simple, clean and distorted to try and get a sense for the differences. I tried to include regular/lighter picking as well as slamming the strings harder in both clean and distorted modes.

In the left channel are the 9v tracks, and in the right channel are the 18v tracks. The cleans are totally unprocessed. Just the guitar into my Line 6 DI, and through GearBox on the "no amp" setting direct into GarageBand. No post-processing was used. The distorted tracks are the same Recto patch i've used on other recordings.

Soundclick: EMG 808 9v vs. 18v

Initial impressions:

My setup makes it hard to do quick pans between the left and right channels, but there are definitely differences in tone and responsiveness. Essentially, everything that's been said about the 18v mod is true... there are much greater dynamics, which you can hear and also see on the waveforms. There's a lot more "air" in the sound when running 18v. It's more apparent on the cleans than the distorted sound. When playing with a lighter touch, it's quieter, and when really slamming the strings, it's louder. In 9v mode, the amplitude of the signal coming out of the guitar is much more even.

Tonally, i actually like the 9v sound a bit better. It has a bit more depth to it to my ears. The 18v has a touch more "presence" at the super-high end of the sonic spectrum. That said, i'd gladly swap more dynamic range and responsiveness for a minor tonal difference that i can tweak back in with EQ.

So there it is... my pseudo-scientific comparison of an EMG 808 in 9v and 18v modes.

My apologies for some audio glitching on the tracks... i haven't really got my system optimized for running audio apps, so there's a bit of weirdness at times. Sometimes it makes it into the recordings, other times not.

[Josh Lawson]

I added tags to this because I think it is a very important thread for many users. This will hopefully help searches in the future.

[Elysian]

hmmm so i could run 4 batteries, a pair in series connected in parallel with a pair in series to double the voltage and battery life? thatd be crazy battery life.

[darren]

Good call on the tagging.

[darren]

Originally Posted by Elysian

hmmm so i could run 4 batteries, a pair in series connected in parallel with a pair in series to double the voltage and battery life? thatd be crazy battery life.

You'd pretty much need to route a whole separate compartment just for the batteries! Maybe just stick a lantern battery in there.

[angus]

I did a similar thing to one of a friend's studio instruments- a custom EMG. I wired a switch in so he could swap on the fly from 9V to 18V. They sound very different, and it allows you to have a lot more freedom to change the tone on the fly in the studio. Not at all practical for live work, but a very very easy mod.

Nice diagram, but the way. Love the realistic shading on the batteries!

I don't know about the guitar pickup stuff, but EMG bass preamps can actually be wired up to 45V (I think Seymour Duncan's can, too). Absolutely no reason to, but you can. I can't remember if their active bass pickups go up to 27 or 45V. I've never heard of someone actually going beyond 18 with them, though.

[neoclassical]

Hmmm. Never thought it would be that easy. I'll have to try it this week. I've been interested in the difference.

Thanks,
Adam

[eleven59]

Couldn't you do this with just one extra battery harness?

Just hook up the positive of one battery and the negative of the other battery to the stock harness, then use the second harness to join the other two poles, and solder and tape the wires on the second harness together?