The active boost circuit favored by Eric Clapton and how to install it


Fender's Stratocaster Mid Boost Kit.

In our previous two installments, we

explored the Fender TBX tone control and

ways to modify it. This month, let's take a

closer look at the Fender active mid-boost,

aka the “Eric Clapton mid-boost" circuit.



Originally called the “MDX mid-boost circuit,"

this device is a 12 dB active boost

circuit that first showed up in the 1983

Fender Elite Stratocaster. The MDX circuit

was developed by James Demeter and

John Carruthers to make single-coil pickups

sound like humbuckers—a typical '80s

thing. The Elite Strat concept only survived

for two years before it was discontinued

because of massive problems with Fender's

Freeflyte Tremolo System.



For me, the Elite Strat is the archetypal

'80s Strat, and I always smile when I get

one on the workbench. The Fender Elite

Strat served as a template for the Eric

Clapton Stratocaster, a model that made

its debut in 1988. Clapton liked the MDX

boost circuit (which he called a “compressor")

and told Fender to keep it for his

signature Strat. He also asked for more

“compression," which prompted Fender

to replace the Elite Strat's standard pickups

with Lace Sensor Gold pickups and

an updated MDX circuit that had been

tweaked to deliver a midrange boost of up

to 25 dB at around 500 Hz.



The EC Strat's features have changed several

times over the years, but the updated MDX

mid-boost remains unchanged, and you can

buy it for about $80 through a Fender dealer

to install in your own Strat. Fender officially

changed the name to “Stratocaster Mid

Boost Kit" (part #005757000). The set comes

with a prewired mid-boost PCB, a TBX tone

control, two pots, a stereo output jack, and

all the small parts you need to connect it to

your guitar.



Here's how Fender describes it:


The Stratocaster Mid Boost Kit

includes all the parts needed to

upgrade your guitar with the Mid

Boost Preamp used on the Eric

Clapton and Buddy Guy Strats.

The system replaces one of the

original tone controls with a variable

“Midrange Boost" control. The

Mid Boost knob adjusts gain from

0 dB (no boost) to 25 dB (for killer

mids). Great for clean and distortion

tones. The TBX tone control is

neutral in the middle position, cuts

treble in one direction and cuts

bass in the other direction.



The component list and layout for Fender's mid-boost

preamp circuit.


Retrofitting Tips

If you want to install a mid-boost system

in your guitar, keep in mind that not only

do you have to install the PCB somewhere,

you also need space for a 9-volt battery to

power the preamp. There are many ways to

place these two components inside a Strat,

and naturally the ideal location depends on

a particular instrument and its routings.



The easiest way is to place the PCB on the

bottom of the Strat's electronics compartment

(below the pots) and the battery in the

trem-spring cavity. While this is the quick-and-dirty way, a more elegant solution is

to route an additional compartment for the

PCB below the neck and middle pickups.

This area is completely covered by the pickguard,

so you won't see it. There are many

variations out there, though, so do a Google

search to find the one you like best.


The DIY Approach

A lot of players want to install an active

boost device in their guitars but complain

about the high price of the Fender kit. If

you're willing to roll up your sleeves, check

out this very cool DIY project that I got from

Australian guitarist Ritchie Laird (reverbnation.com/ritchielaird). He developed a mod

for an active, EC-style mid booster that's

even more flexible than the Fender kit. Best

of all, it won't break the bank.



For this project, Laird uses an inexpensive,

onboard acoustic-guitar preamp called

the Belcat EQ-505R (belcat.com). You can

often find the Belcat preamp on eBay

for less than $10. And you can download

Laird's super-detailed, step-by-step instructions

from my site (singlecoil.com/docs/active_strat.pdf). I've had feedback from

players all over the world who've tried this

project, and they all loved it.



Next month, we'll talk about how you can

make your own version of the Fender Delta

Tone. So stay tuned for more Strat mods—and in the meantime, keep on modding!



Dirk Wacker

Dirk Wacker lives in Germany and has been addicted to

all kinds of guitars since the age of 5. He is fascinated

by anything related to old Fender guitars and amps. He

plays country, rockabilly, and surf music in two bands,

works regularly as a session musician for a local studio,

and writes for several guitar mags. He is also a hardcore

DIY-er for guitars, amps, and stompboxes, and he runs

an extensive webpage—singlecoil.com—on the subject.

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