Aion COMET Manuel utilisateur

COMET VINTAGE DISTORTION 1

PROJECT NAME

COMET

BASED ON

EFFECT TYPE

PROJECT SUMMARY

DOCUMENT VERSION

BOSS®DS-1 Distortion

A classic distortion pedal that has been in continuous production for over 40 years, blending ideas from

the Big Muff, RAT and Distortion+.

Distortion 1.0.0 (2021-10-22)

BUILD DIFFICULTY

Easy

Actual size is 2.3” x 1.86” (main board) and 2.3” x 0.86” (bypass board).

COMET VINTAGE DISTORTION 2

TABLE OF CONTENTS

1Project Overview 7Drill Template

2Introduction & Usage 8Enclosure Layout

3-4 Parts List 9Wiring Diagram

5Build Notes 10 Licensing

6Schematic 10 Document Revisions

INTRODUCTION

The Comet Vintage Distortion is a clone of the classic orange BOSS®DS-1 Distortion, one of their

earliest compact effects in continuous production since 1978.

Design-wise, the DS-1 is an amalgamation of a few different ideas. The initial transistor gain stage is

very similar to the Big Muff, as is the tone section with its bass/treble balance control. The IC gain stage

followed by diode-to-ground hard clipping is similar to early op-amp distortion circuits like the MXR

Distortion+ or Pro Co RAT.

During the past four decades, it has undergone several revisions. The basic schematic structure has

stayed the same throughout its production, but when the original IC was discontinued in the early

‘90s, the op-amp gain stage was redesigned to use a standard dual op-amp. Previously it had used a

Toshiba TA7136P special-purpose “RIAA preamp” that was technically not even a true op-amp, so this

necessitated several changes. They also re-voiced the circuit at the same time, reducing the bass and

lowering the clipping threshold slightly.

The result is that there is a significant difference between the “pre-1994” and “post-1994” versions of

the circuit. The pre-’94 version remains highly regarded, while the post-’94 circuit is responsible for the

DS-1’s reputation as a poor-quality beginner’s pedal. The good news is that the voicing changes are fully

reversible, and it’s possible to get the post-’94 dual op-amp version to sound just as good as the pre-’94

version with a handful of capacitor and diode changes.

The Comet is based on the dual op-amp version of the circuit. The default build makes a few parts

substitutions to make it nearly identical to the pre-’94 circuit. If you want to use the TA7136P chip for

an exact replica of the pre-’94 DS-1, the legacy version of the Comet is still available and supports either

configuration. However, this updated version drops support for the old IC because it’s almost impossible

to find today and the build process is much more streamlined without the option.

USAGE

The Comet has three controls and one toggle:

• Distortion controls the amount of gain from the op-amp stage that is clipped by the diodes.

• Tone pans between a bass emphasis and a treble emphasis, with a mid-scoop centered at 550 Hz.

• Level sets the overall output of the effect.

• Clipping selects between three different sets of hard-clipping diodes.

COMET VINTAGE DISTORTION 3

PARTS LIST

This parts list is also available in a spreadsheet format which can be imported directly into Mouser for

easy parts ordering. Mouser doesn’t carry all the parts—notably potentiometers—so the second tab lists

all the non-Mouser parts as well as sources for each.

View parts list spreadsheet →

PART VALUE TYPE NOTES

R1 1k Metal film resistor, 1/4W

R2 470k Metal film resistor, 1/4W

R3 10k Metal film resistor, 1/4W

R4 100k Metal film resistor, 1/4W

R5 470k Metal film resistor, 1/4W

R6 10k Metal film resistor, 1/4W

R7 22R Metal film resistor, 1/4W

R8 100k Metal film resistor, 1/4W

R9 47k Metal film resistor, 1/4W

R10 100k Metal film resistor, 1/4W

R11 4k7 Metal film resistor, 1/4W

R12 2k2 Metal film resistor, 1/4W

R13 6k8 Metal film resistor, 1/4W

R14 2k2 Metal film resistor, 1/4W

R15 6k8 Metal film resistor, 1/4W

R16 10k Metal film resistor, 1/4W

R17 1M Metal film resistor, 1/4W

R18 10k Metal film resistor, 1/4W

R19 1k Metal film resistor, 1/4W

R20 100k Metal film resistor, 1/4W

R21 10k Metal film resistor, 1/4W

R22 10k Metal film resistor, 1/4W

R23 100R Metal film resistor, 1/4W

RPD 2M2 Metal film resistor, 1/4W Input pulldown resistor.

LEDR 4k7 Metal film resistor, 1/4W LED current-limiting resistor. Adjust value to change LED brightness.

C1 47n Film capacitor, 7.2 x 2.5mm

C2 47n Film capacitor, 7.2 x 2.5mm

C3 250pF Ceramic capacitor, X5F

C4 OMIT Use 100n for the Big Muff clipping mod. Leave empty otherwise.

C5 68n Film capacitor, 7.2 x 2.5mm

C6 100pF MLCC capacitor, NP0/C0G

C7 470n Film capacitor, 7.2 x 3mm

COMET VINTAGE DISTORTION 4

PARTS LIST, CONT.

PART VALUE TYPE NOTES

C8 470n Film capacitor, 7.2 x 3mm

C9 10n Film capacitor, 7.2 x 2.5mm

C10 22n Film capacitor, 7.2 x 2.5mm

C11 100n Film capacitor, 7.2 x 2.5mm

C12 47n Film capacitor, 7.2 x 2.5mm

C13 1uF Film capacitor, 7.2 x 3.5mm

C14 47uF Electrolytic capacitor, 5mm Reference voltage filter capacitor.

C15 100uF Electrolytic capacitor, 6.3mm Power supply filter capacitor.

C16 100n MLCC capacitor, X7R Power supply filter capacitor.

D1 1N5817 Schottky diode, DO-41

D2 OMIT Use 1N914 for the Big Muff clipping mod. Leave empty otherwise. See

build notes for more info.

D3 OMIT

D4 1N914 Fast-switching diode, DO-35

D5 1N914 Fast-switching diode, DO-35

D6 BAT46 Schottky diode, DO-35

D7 1N914 Fast-switching diode, DO-35

D8 BAT46 Schottky diode, DO-35

D9 3mm LED LED, 3mm, red diffused

D10 3mm LED LED, 3mm, red diffused

Q1 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses 2SC2248.

Q2 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses 2SC2248.

Q3 2N5088 BJT transistor, NPN, TO-92 Substitute. Original uses 2SC2248.

IC1 NJM3404AD Operational amplifier, DIP8 Can substitute JRC4580D.

IC1-S DIP-8 socket IC socket, DIP-8

DIST. 100kB 16mm right-angle PCB mount pot

TONE 25kB 16mm right-angle PCB mount pot The original uses 20kB if you can find it, but 25kB is much more common

and will work the same.

LEVEL 100kB 16mm right-angle PCB mount pot

CLIP SPDT cntr off Toggle switch, SPDT center off

LED 5mm LED, 5mm, red diffused

IN 1/4" stereo 1/4" phone jack, closed frame Switchcraft 112BX or equivalent.

OUT 1/4" mono 1/4" phone jack, closed frame Switchcraft 111X or equivalent.

DC 2.1mm DC jack, 2.1mm panel mount Mouser 163-4302-E or equivalent.

BATT Battery snap 9V battery snap Optional. Use the soft plastic type—the hard-shell type will not fit.

FSW 3PDT Stomp switch, 3PDT

ENC 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1.

COMET VINTAGE DISTORTION 5

BUILD NOTES

Pre-1994 version

The default parts list for the Comet is for the pre-1994 version, the only difference being the op-amp

since the original TA7136P IC is no longer produced and very hard to find. This involves changing three

capacitors (C5, C6 and C7).

The original diodes clipped near 1V, but since no equivalents are readily available, it’s recommended to

use 1N914 (0.65V) and BAT46 (0.35V) in series for each diode pair. The “stock” clipping mode is the up

position of the toggle switch, and the down position is a little more compressed and lower volume.

Pre-1994 version

If you’d like to build the post-1994 version of the DS-1, make the following substitutions:

• C5: 470n →68n

• C6: 250pF →100pF

• C7: 1uF →470n

Additionally, the “stock” clipping mode is now the down position of the toggle switch. You can change

out D6 and D8 for normal 1N914 diodes to raise the clipping threshold a little bit, providing more

contrast between the up and down positions.

IC selection

The DS-1 has undergone a few other minor circuit changes after the major revision in 1994, mostly

related to the IC:

• 1994-2000: Rohm BA728N

• 2000-2006: Mitsubishi M5223AL

• 2006-2016: New Japan Radio NJM2904L, later changed to NJM3404L, exact year unknown

• 2016-present: New Japan Radio NJM4580 (JRC4580)

The first four are single-in-line (SIL) dual op-amps, although the NJM2904 and NJM3404 have a DIP-8

version available. Since 2016 when BOSS made the switch to SMD, the DS-1 has used the JRC4580. It’s

recommended to use either the NJM3404 or NJM4580 in this project.

Big Muff clipping mod

The amplifier stage formed by Q2 is identical to the first transistor stage of the Big Muff. The stock DS-1

does not have any clipping in this stage, but if you want to experiment, space has been provided to add

the two diodes and capacitor and convert it into something more like stage 2 or 3 of the Big Muff with

feedback diode clipping.

To try this modification, use 1N914 for D2 and D3 and a 100n film capacitor for C4. Omit these three

parts for the stock DS-1 circuit.

SCHEMATIC

COMET VINTAGE DISTORTION 6

GND

2M2

1N5817

100uF

100kB

GND

100kB

25kB

+9V

100n

100R 10k

10k

47uF

GND GND

47n

470k

2N5088

10k

47n

100k

GND GND

2N5088

470k

250pF

OMIT

10k

22R

GND

470n

100k

47k

1N914

GND

100k

250pF

4k7

1uF

GND

2k2

470n

10n

6k8

22n

2k2

6k8

100n

10k

47n

2N5088

10k

1uF

GND

100k

GND

VB VB

OUT

RPD

C15

DISTORTION

LEVEL

TONE

C16

R23 R21

R22

C14

R6R7

IC1B

NJM3404AD

IC1A

R10

R11

R12

D5D6

D7D8

D10

CLIP

R13

C10

R14

R15

C11

R16

C12

R17

R18

R19

C13

R20

GND

COMET VINTAGE DISTORTION 7

DRILL TEMPLATE

Cut out this drill template, fold the edges and tape it to the enclosure. Before drilling, it’s recommended

to first use a center punch for each of the holes to help guide the drill bit.

Ensure that this template is printed at 100% or “Actual Size”. You can double-check this by measuring

the scale on the printed page.

Top jack layout assumes the use of closed-frame jacks like the Switchcraft 111X. If you’d rather use

open-frame jacks, please refer to the Open-Frame Jack Drill Template for the top side.

LED hole drill size assumes the use of a 5mm LED bezel, available from several parts suppliers. Adjust

size accordingly if using something different, such as a 3mm bezel, a plastic bezel, or just a plain LED.

x: -0.65, y: +1.71 x: 0.65, y: +1.71

ø9/32” ø9/32”

x: 0, y: +0.66

ø9/32”

x: 0, y: -1.20

ø15/32”

x: -0.775, y: -1.20

ø5/16”

CENTER (0,0)

ø3/8” ø1/2”

0.385”

0.625” 0.625”

ø3/8”

OUT DC IN

125B

VOLUME

CLIPTONE

DISTORTION

FOOTSWITCHLED

x: +0.85, y: +0.66

ø1/4”

0 1 2

0 1

INCH

COMET VINTAGE DISTORTION 8

ENCLOSURE LAYOUT

Enclosure is shown without jacks. See next page for jack layout and wiring.

125B

COMET VINTAGE DISTORTION 9

WIRING DIAGRAM

125B

IN +VGND N.C. N.C. OUT

PCB

GND +V +V JACK GND JACK

OUTIN

GND GND PCB

OUT

Shown with optional 9V battery. If battery is omitted, both jacks can be mono rather than one being stereo.

Leave the far-right lug of the DC jack unconnected.

COMET VINTAGE DISTORTION 10

LICENSE & USAGE

No direct support is offered for these projects beyond the provided documentation. It’s assumed

that you have at least some experience building pedals before starting one of these. Replacements and

refunds cannotbe offered unless it can be shown that the circuit or documentation are in error.

All of these circuits have been tested in good faith in their base configurations. However, not all the

modifications or variations have necessarily been tested. 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 specifically noted. 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 without prior arrangement, 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 industry needs more transparency, not less!)

DOCUMENT REVISIONS

1.0.0 (2021-10-22)

Initial release.

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