Aion Electronics Comet Distortion Manual

Comet Distortion
BOSS DS-1 Distortion
Overview
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.
Modifications & 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 modifications 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.
DS-1 DISTORTION / COMET DISTORTION
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-
modified 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 modifications.
Comet Project Link
1