Mod 2: Alter TS9 and SD-1 Distortion by Swapping Diodes
Tools and Parts for This Mod
• Various numbers and types of diodes and/or LEDs, depending
on which symmetrical or asymmetrical mod you decide to do
You can get different shades of
distortion by swapping clipping
diodes in your Tube Screamer
or Super Overdrive. For
example, replacing the existing
diodes with germanium diodes
will yield a compressed, smooth
fuzz sound. In contrast, silicon
diodes (1n4148, 1n4001,
1n914, etc.) tend to provide a
crisper, tighter, more focused
sound. LEDs sound warmer,
offer a great crunch, and usually
make the pedal sound louder.
You can also experiment
with different diode configurations.
Two types of clipping can
be achieved through different
configurations: symmetrical and
clipping—the type of clipping
achieved in a stock Boss SD-1
circuit (see Fig. 2)—tends
to yield a more dynamic and
responsive overdrive resembling
the feel and response of an amp
overdrive. You can get asymmetrical
clipping by putting two
in parallel with one
diode oriented in
the opposite direction
(as shown in the
Fig. 2: Asymmetrical Clipping. A stock Boss
SD-1 schematic (left), and an SD-1 schematic
with an LED swapped out in place of the original
clipping diode to yield a louder, warmer, more
responsive feel (right).
You can also achieve
by removing an
original diode and
replacing it with an
LED, which tends
to yield more headroom
To get more
headroom out of a symmetrical
clipping circuit—the type of
clipping achieved in an Ibanez
TS9 circuit (see Fig. 3)—you
can add an extra set of diodes in
series with the original diodes,
or you can change both diodes
out for LEDs (as shown in the
diagrams). However, keep in
mind that this will change how
much clipping you hear.
Fig. 3: Symmetrical Clipping. A stock Ibanez TS9 schematic with two silicon diodes (left), a TS9 schematic modded with two sets of series-wired diodes running parallel to each other to achieve more volume and headroom with slightly less clipping (middle), and a TS9 schematic with two LEDs running in parallel instead of the original silicon diodes, which yields more headroom and volume, with a warmer response.
When replacing diodes,
make sure you orient them correctly.
The stripe on the diode
always goes on the same side as
the bar at the tip of the triangle
on the diode symbol that’s
stenciled on the circuit board.
For LEDs, the short leg goes
towards the bar.
Now that you know more than
you probably ever wanted to know
about diode configurations, we’ll
show you how to do some diode
mods on a TS9 and an SD-1.
Let’s start by changing a Tube
Screamer’s clipping from stock
symmetrical to asymmetrical by
adding a diode pair in series.
Photo 6 (left): Diodes 1 and 2 on a TS9 circuit board. Photo 7 (top middle): Wire two diodes in series by making sure their black stripes are oriented in the same direction and then wrapping the middle leads together. Photo 8 (bottom middle): Solder the diode legs together and bend the outer legs for easy installation. Photo 9. (Right) Solder the series-wired diodes’ legs back into the holes vacated in step 2. Note the black heat-shrink wrap protecting the new solder connection.
1. Locate the diodes on your
TS9’s circuit board. See Photo 6.
2. Desolder diode 1 (D1) or
diode 2 (D2)—it doesn’t matter
which comes first. Note: I recommend
using a felt-tip marker
to mark which components you
need to desolder on the underside
of the circuit board.
3. Wire two diodes in series—either pair one stock diode
with a new one or pair two
brand-new diodes—by twisting
their legs together as shown
in Photo 7. Note: See how the
black stripes are both on the left
hand side of each diode? This is
very important to get right—your
pedal won’t work unless they are
4. Solder the twisted-together
legs as shown in Photo 8, and
then place heat-shrink wrap or
electrical tape on the exposed
solder joint (not shown), and
bend the legs as shown.
5. Place the series-wired diodes’
legs back through the D1 or D2
holes (depending on which you
removed in step 2) and solder
them in place. See Photo 9.
Note: Make sure the diodes’ black
stripes are on the same side as
the bar on the tip of the triangle
marked on the board.
Now that you know how to
place diodes in series, you can
read the schematics in Figures 2
and 3 and execute any of them
that use series wiring.
Photo 10: On the Boss SD-1’s circuit board, diodes D4, D5, and D6 can be altered in various asymmetrical and symmetrical arrangements for different feels and gain types.
The SD-1 circuit is different
from the TS9 in that it comes
standard with an asymmetrical
clipping arrangement. Take a
look at the circuit layout in
Photo 10. D4, D5, and D6 are
the clipping diodes. D5 and D6
are already in series with each
other and in parallel with D4.
If you want to make this a symmetrical
arrangement, you can
remove D5 or D6—it doesn’t
matter which—and place a
jumper wire where it used to be.
If you want a symmetrical
arrangement with more
headroom, I suggest leaving
D5 and D6 alone and adding a
diode in series with D4, just as
we did in steps 3 and 4 in the
previous “TS9 Asymmetrical
Clipping Mod.” If you want
more clipping with an asymmetrical
setup, you could also
place a diode in series with
D4 and D6. You can try many
variations of series and parallel
pairings of different types of
diodes, and it’s a bit easier with
the SD-1 as compared to the
TS9 because of the SD-1’s setup
and its roomier circuit board.
So don’t be afraid to experiment—just make sure you don’t
put your diodes in backward. If
you do, it won’t hurt anything,
but your pedal won’t work
right. All you have to do is turn
them around and you should be
good to go.