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.
