COMET VINTAGE DISTORTION
2
TABLE OF CONTENTS
1
Project Overview
7
Drill Template
2
Introduction & Usage
8
Enclosure Layout
3-4
Parts List
9
Wiring Diagram
5
Build Notes
10
Licensing
6
Schematic
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
.
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
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.
