Aion Electronics Comet Distortion Manual - Page 3
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Build Notes
With the FET switching in the original, there are two capacitors in series here, 470n and 47n. A
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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.
Electrolytic or film. The original uses electrolytics as coupling capacitors, so for "vintage tone" the lower
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fidelity of electrolytic capacitors may be desired. The layout has room for full-sized film capacitors, but the
polarity is marked if you want to use electrolytics.
Don't use both of these. Hopefully this goes without saying, but you only want to use one of these op amps
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depending on which version you want to build. Bad things might happen if you were to use both of them.
Stacking diodes: The original diodes in the MIJ version are 1S2473, which are long out of production and
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very difficult to find. 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.
Your choice. LEDs are very commonly used as alternate clipping diodes in a DS-1 mod.
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Modifications
The BOSS DS-1 is one of the most frequently modded pedals out there, and on a personal note, was both the
first guitar pedal I owned and the first 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 first thing upgraded in most modifications, 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 fidelity).
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
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 amplified by the op amp.
DS-1 DISTORTION / COMET DISTORTION
Mod 2
All changes from Mod 1, plus...
C3
470pF
C4
100n
C5
220pF
R10
2k4
R12
1k5
R23
20k
series
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