Aion Electronics Comet Distortion User manual

1DS-1 DISTORTION / COMET DISTORTION
Comet Distortion
BOSS DS-1 Distortion
Controls & Usage
The DS-1’s controls are standard drive/distortion controls:
• Drive controls the amount of gain from the op amp that is fed into the diode clipping stage.
• Tone is similar to the Big Muff tone control, panning between a bass and treble emphasis.
• Volume controls the overall output.
Modications&Experimentation
The Clipping switch mod allows you to set up a second set of diodes to toggle back and forth from stock.
Extra pads have been provided so you can stack two diodes in a row if desired. (The middle two pads are
connected in each diode.) If you use a SPDT center-off switch, the middle position becomes a diode lift mode,
but you can also use a regular SPDT if you don’t care about this.
The pre-1994 version uses a TA7136P single-in-line op amp. The revised post-1994 circuit uses a poor-
quality dual op amp, and one of the most common modications is to switch this out with a better op amp
such as an OPA2134 or JRC4558. However, this is a tricky mod and requires an awkward breakout adapter,
since the dual op amp is also a single-in-line style. I elected to build the layout around a DIP8 dual op amp to
accommodate. (Ironically, then, the only version of the DS-1 that you can’t build with this PCB is the one you
can buy for $40 from any music store today.)
Due to the similarity between the DS-1’s pregain stage and the Big Muff’s clipping gain stages, this PCB has
space for a few extra diodes and capacitors to convert this stage to Big Muff specs. (Thanks to Build Your Own
Clone for this mod!) This will tighten up the bass and change the distortion character.
The Comet Distortion project is a clone of the classic
orange BOSS DS-1 Distortion, in continuous production
since 1978. The circuit has a few different things going
on—the pregain and tone sections are very similar to the
Big Muff, while the diode-to-ground hard clipping is similar
to circuits like the Distortion+.
The DS-1 had a major circuit revision in 1994 that
dropped the original single op-amp in favor of a dual,
along with some other changes to accompany the new
op-amp. The original “Made in Japan” version is very
well-regarded, while the revised “post-1994” version is
not as much. However, it is one of the most frequently-
modied pedals out there, with great mods available from
Keeley, Analogman and Monte Allums. The circuit itself
is a great one—the BOSS pedal just suffers from cheap
components.
The Comet Distortion will allow you to build either the
pre- or post-1994 versions of the circuit, as well as
incorporating most of the popular modications.
CometProjectLinkOverview

2DS-1 DISTORTION / COMET DISTORTION
Parts (vintage / modern values)
Resistors
R1 1k
R2 470k
R3 10k
R4 100k
R5 470k
R6 10k
R7 22R
R8 100k
R9 100k
R10 4k7
R11 27k / (omit)
R12 2k2
R13 6k8
R14 2k2
R15 6k8
R16 10k
R17 1M
R18 10k
R19 1k
R20 100k
R21 10k
R22 10k
R23 (omit) / 47k
R24 (omit) / 1k
RPD 1M to 2M2
LEDR 4k7
Semiconductors
IC1 (vintage) TA7136P 3
IC2 (modern) TL072 3
Q1-Q3 2N5088
D1 1N4002
D2, D3 1N914 4
D4, D5 3mm LED 5
D6 1N914
(modern only)
DX1, DX2 (omit)
LED 5MM
Potentiometers
Distortion 100kB
Tone 25kB
Volume 100kB
Other
CLIP SPDT center off
Capacitors
C1 47n
C2 42n 1
C3 250pF
C4 470n / 68n
C5 250pF / 100pF
C6 150pF / (omit)
C7 1uF / 470n 2
C8 470n
C9 10n
C10 22n
C11 100n
C12 47n
C13 1uF 2
C14 100uF
C15 47uF
CX1 (omit)
See following page for footnotes.
Additional Part Notes
• Capacitors are shown in nanofarads (n or nF) where appropriate. 1000n = 1uF. Many online suppliers do
not use nanofarads, so you’ll often have to look for 0.047uF instead of 47n, 0.0056uF instead of 5n6, etc.
• The PCB layout assumes the use of lm capacitors with 5mm lead spacing for all values 1nF through
470nF. I prefer EPCOS box lm or Panasonic ECQ-B/V-series.
• Potentiometers are Alpha 16mm right-angle PCB mount.
• Switches are Taiway (Small Bear) or Mountain Switch (Mouser) brand with solder lugs. I prefer the short-
toggle variety, but that’s just a matter of aesthetics.
• I recommend using these dust covers / insulators from Small Bear to insulate the back of the pots from
the board and prevent shorts. If you don’t use these, use some electrical tape or cardboard to act as
insulation. The right-angle pots will make direct contact with the solder pads otherwise.

3DS-1 DISTORTION / COMET DISTORTION
Build Notes
1With the FET switching in the original, there are two capacitors in series here, 470n and 47n. A series
calculation puts the “consolidated” value for this at 42n. However, since 42n is a pretty rare value for a
capacitor, the more common 47n can be used instead and won’t be noticeably different.
2Electrolyticorlm. The original uses electrolytics as coupling capacitors, so for “vintage tone” the lower
delity of electrolytic capacitors may be desired. The layout has room for full-sized lm capacitors, but the
polarity is marked if you want to use electrolytics.
3Don’tusebothofthese. Hopefully this goes without saying, but you only want to use one of these op amps
depending on which version you want to build. Bad things might happen if you were to use both of them.
4 Stackingdiodes:The original diodes in the MIJ version are 1S2473, which are long out of production and
very difcult to nd. There is not anything special about these diodes to warrant tracking them down and
paying high prices for them. Their notable characteristic is that they clip between 1 and 1.2 volts, which is far
higher than the standard 1N914s used in the modern DS-1 and will give a more open and less compressed
sound which is critical for a MIJ clone. I recommend combining a 1N914 (0.6V) and a BAT41 (0.4V) in series
on each side to get an equivalent clipping threshold, which will require standing them on end. You could also
try a BA243, BA278 or BA282 here, which all clip at around 0.9v and are easy to come by.
5Yourchoice. LEDs are very commonly used as alternate clipping diodes in a DS-1 mod.
Modications
The BOSS DS-1 is one of the most frequently modded pedals out there, and on a personal note, was both the
rst guitar pedal I owned and the rst one I ever modded. Despite its popularity, the off-the-shelf $40 version is
shrill, brittle and uneven. Fortunately it doesn’t take much to turn it into a very good distortion pedal!
The IC is the rst thing upgraded in most modications, and the single thing that makes the biggest difference.
Since this layout was made for a DIP8 op amp rather than a single-in-line like the original post-’94 version, you
have an abundance of excellent options available, but a couple of good choices are the TL072, JRC4558, and
Burr-Brown OPA2134 (more expensive but much higher delity).
Beyond that, here are a few value changes inspired by mods from Keeley, Monte Allums and Analogman.
Mod 1
IC1 OPA2134
C1 100n
C2 100n
C7 1uF
C10 47n
C12 100n
Mod 2
All changes from Mod 1, plus...
C3 470pF
C4 100n
C5 220pF
R10 2k4
R12 1k5
R23 20k
BigMuffmod: The DS-1 has a couple of building blocks in common with the Big Muff, notably the tone control
and the gain stage before the op amp. Some have experimented with adding a couple of parts to the DS-1’s
gain stage to make it identical to a Big Muff clipping stage. To do this, put a 100n cap in CX1 and two 1N914s
for DX1 and DX2. This will clip the signal before it gets amplied by the op amp.

4DS-1 DISTORTION / COMET DISTORTION
Schematic(pre-1994values)
+9V
GND
VA
100kB
25kB
100kB
2M2
4k7
1k
470k
10k
100k
470k
10k22R
100k
100k
4k7
8k62k2
2k2
6k8
10k
1M
10k
1k
100k
10k
10k
47n
47n
250pF
470n
250pF
150pF
1uF
470n
10n 22n
100n
47n
1uF
JRC4558D
5MM
GND
TA7136P
8805N28805N2
2N5088
Fu74Fu001
DNGDNGDNG
VA
GND
+9V
GNDGND
+9V
GND
VA
27k
+9V
GND
VA
VA
VA
VA VA
DNGDNG
+9V
VA
47k
D6
D2
D3
D4
D5
GND
100n
1k
+9V
IN
OUT
SW
+9V
DIST
1
2
3
TONE
1
2
3
VOLUME
1
2
3
RPD
LEDR
R1
R2
R3
R4
R5
R6R7
R8
R9
R10
31R21R
R14
R15
R16
R17
R18
R19
R20
R21
R22
C1
C2
C3
C4
C5
C6
C7
C8
C9 C10
C11
C12
C13
2 3
1
IC2A
84
6 5
7
IC2B
LED
3 2
6
IC1A
15
21
3
74
51C41C
R11
2
3
1
CLIP
R23
C1
D1
D2
R24
D1
1N4001

5DS-1 DISTORTION / COMET DISTORTION
GeneralBuildInstructions
These are general guidelines and explanations for all Aion Electronics DIY projects, so be aware that not
everything described below may apply to this particular project.
Build Order
When putting together the PCB, it’s recommended that you do not yet solder any of the enclosure-mounted
control components (pots and switches) to the board. Instead, follow this build order:
1. Attach the audiojacks, DCjack and footswitch to the enclosure.
2. Firmly attach the pots and switches to the enclosure, taking care that they are aligned and straight.
3. Push the LED1 into the hole in the enclosure with the leads sticking straight up, ensuring that the at side
is oriented according to the silkscreen on the PCB.
4. Fit the PCB onto all the control components, including the leads of the LED. If it doesn’t t, or if you need
to bend things more than you think you should, double-check the alignment of the pots and switches.
5. Once you feel good about everything, solderthemfromthetop2as the last step before wiring. This way
there is no stress on the solder joints from slight misalignments that do not t the drilled holes. You can
still take it out easily if the build needs to be debugged, but now the PCB is “custom-t” to that particular
enclosure.
6. Wire everything according to the wiring diagram on the last page.
1FortheLED: You can use a bezel if you’d like, but generally it’s easier just to drill the proper size of hole
and push the LED through so it ts snugly. If you solder it directly to the PCB, it’ll stay put even if the hole is
slightly too big. Make absolutely sure the LED is oriented correctly (the at side matches the silk screen) before
soldering, as it’ll be a pain to x later! After it’s soldered, clip off the excess length of the leads.
2Noteonsolderingthetoggleswitch(es): It will require a good amount of solder to ll the pads. Try to be as
quick as possible to avoid melting the lugs, and be prepared to feed a lot of solder as soon as the solder starts
to melt. I recommend waiting 20-30 seconds between soldering each lug to give it time to cool down.
“RPD”and“LEDR”resistors
The resistors marked “RPD” and “LEDR” are generally not original to the circuit and can be adjusted to
preference. “RPD” is the pulldown resistor to help tame true-bypass popping, while “LEDR” controls the
brightness of the LED. I generally use 2.2M for the pulldown resistor and 4.7k for the LED resistor.
Sockets
Since double-sided boards can be very frustrating to desolder, especially components with more than 2 leads,
it is recommended to use sockets for all transistors and ICs. It may save you a lot of headaches later on.

6DS-1 DISTORTION / COMET DISTORTION
Drilling&Placement
Print this page and have an adult cut out the drilling template below for you. Tape it to the enclosure to secure
it while drilling. Note that the holes are shown slightly smaller than they need to be, so drill out the holes as
shown and then step up until they are the correct size for the components.
Parts Used
• Switchcraft #111A enclosed jacks
• Kobiconn-style DC jack with internal nut
Hammond1590B
(bottom/inside view)

7DS-1 DISTORTION / COMET DISTORTION
Standard Wiring Diagram
This diagram shows standard true-bypass wiring
with a 3PDT switch. When the switch is off, the
input of the circuit is grounded and the input jack
is connected directly to the output jack.
The SW pad is the cathode connection for the
LED. This will connect to ground to turn it on
when the switch is on. Usage of the on-board
LED connection is not required if you have
specic placement needs for your enclosure,
but’s incredibly convenient.
The wiring diagram also makes use of star
grounding principles where all of the grounds
connect to a single ground point (in this case the
sleeve of the input jack). This is best practice
to avoid added noise caused by improper
grounding. The sleeve of the output jack is
unconnected.
If using a painted or powdercoated enclosure,
makesurebothjackshavesolidcontactwith
bare aluminum for grounding purposes. You may
need to sand off some of the paint or powdercoat
on the inside in order to make this happen.
Make sure to double-check the markings of the
pads on the PCB for your particular project – they
are not always in the order shown here!
IN GND OUT SW
+9V
SLEEVE
TIP
TIP
License/Usage
NodirectsupportisofferedforthesePCBsbeyondtheprovideddocumentation.It is assumed that you
have at least some experience building pedals before starting one of these. Replacements and refunds will not
be offered unless it can be shown that the circuit or documentation are in error. I have in good faith tested all of
these circuits. However, I have not necessarily tested every listed modication or variation. These are offered
only as suggestions based on the experience and opinions of others.
Projectsmaybeusedforcommercialendeavorsinanyquantityunlessspecicallynoted. No bulk
pricing or discounting is offered. No attribution is necessary, though a link back is always greatly appreciated.
The only usage restrictions are that (1)youcannotresellthePCBaspartofakit, and (2)youcannot
“goop”thecircuit,scratchoffthescreenprint,orotherwiseobfuscatethecircuittodisguiseitssource.
(In other words: you don’t have to go out of your way to advertise the fact that you use these PCBs, but please
don’t go out of your way to hide it. The guitar effects pedal industry needs more transparency, not less!)