Boss BD- 2
Blues Driver
MODS
two FETs facing each other followed by a matically. For example, if we want a fuzzi-bipolar transistor. There are two of these er type of distortion, we want to increase
types of gain stages in the BD- 2, con- the bass before it is clipped. Then, we clip
trolled by a dual gang 250k pot wired as the signal as much as possible without
a variable resistor. Just like the IC opamp creating a lot of noise or oscillations.
circuits, there is a resistor/capacitor pair
going to ground that will also help set a
frequency to clip. This pair will also help
set the gain, though they are fixed values
in the BD- 2. R31 and C22 are the pair for
the first stage, while R15 and C9 are the
pair for the second stage.
BY BRIAN WAMPLER
The Boss Blues Driver is one of those pedals that everybody has owned or at least
played through once. I’d venture to say
it’s nearly as popular as the beloved Tube
Screamer. While many players like the
sound of the stock pedal just fine, many
other guitarists like the basic tone but just
want it better—more organic, responsive
and dynamic. Some feel that there are
just way too many high frequencies in
the pedal, making it sound brittle, especially with a single coil guitar into a clean,
Fender-type amp. Luckily, there are modifications we can do to make the pedal
much better.
We know that EQ before clipping determines the clipping feel, tonality, and
response (distortion/overdrive) quite dra-
R31 and C22 in this first gain stage set a
frequency of just a hair over 700hz. This
is a normal frequency for most overdrives
and distortion. If you want more fuzziness,
increase this cap to .22uf (microfarad) or
larger. If you want a tighter crunchier type
of tone, make the cap smaller. If you plug
in these values to my calculator at indy-
guitarist.com/filter.htm you will see the
frequencies you can affect.
The Circuit
Before we get into the mods, let’s break
down the circuit a bit and see what is
going on. Looking at the schematic we
see that it is essentially two cascaded
discrete opamps, which are then followed by a standard opamp for gain
recovery, bass boosting, and buffering of
the signal. Of course, this is after it goes
through a discrete buffer.
-10dB
-20dB
-30dB
-40dB
In layman’s terms, a discrete opamp is
similar to the IC chip version. It does the
same thing, just in a simpler fashion that
some feel is more responsive and less
“sterile” feeling and sounding. It uses
0dB
-50dB
10Hz
Figure 1
100Hz
1000Hz
10000Hz
After this first gain stage, we go through
what first looks like an odd tone filtering stage. It is actually a Fender-type
3-band tonestack with fixed values (with
the treble on 0 and the bass and mid on
10). This is a really cool thing to mess
with if you want to go hog wild, because
you can add trim pots in place of R37
(use a 250k trim pot for treble), R50 (use
a 1M trim pot for bass), and R51 (use a
25k trim pot for mids). In addition, you
can change the ‘slope’ resistor, R36, to a
33k, C34 and C35 to a .022uf, and change
C26 to a 470pf in order to get more of a
Marshall type of tonality before the signal
is clipped. When you are replacing these
