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PROJECT NAME
CHROMA
BASED ON
BOSS
®
SP-1 Spectrum
EFFECT TYPE
Parametric equalizer / boost
PROJECT SUMMARY
One of the rarest BOSS effects, a single-band swept-frequency EQ. Modified to boost the overall signal
level so it can be used as a boost pedal if desired.
Actual size is 2.3" x 1.86" (main board) and 2.3" x 0.86" (bypass board).
This project requires a dual 10kA/10kC potentiometer, which is not available from any of the
normal suppliers. It's easy to make your own, but make sure to read the instructions on page 5
before undertaking the project.
CHROMA PARAMETRIC BOOST
BUILD DIFFICULTY
Easy
DOCUMENT VERSION
1.0.0 (2021-10-22)
IMPORTANT NOTE
1
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Summary of Contents for aion CHROMA
- Page 1 This project requires a dual 10kA/10kC potentiometer, which is not available from any of the normal suppliers. It’s easy to make your own, but make sure to read the instructions on page 5 before undertaking the project. CHROMA PARAMETRIC BOOST...
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Page 2: Table Of Contents
Spectrum knob while a signal is being passed. The updated version of the Chroma adds one new feature: the output volume has been increased and it now includes a volume knob. This way, the output volume can be precisely trimmed for unity gain (which is inexact in the original Spectrum depending on where the Balance control is set), or it can be used as a booster with an adjustable frequency emphasis. -
Page 3: Parts List
Film capacitor, 7.2 x 3.5mm Original uses 4.7uF. There is space for the 4.7uF film capacitor, but 1uF is sufficient. 47pF MLCC capacitor, NP0/C0G Film capacitor, 7.2 x 3.5mm 47uF Electrolytic capacitor, 5mm Reference voltage filter capacitor. CHROMA PARAMETRIC BOOST... - Page 4 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. 3PDT Stomp switch, 3PDT 125B Enclosure, die-cast aluminum Can also use a Hammond 1590N1. CHROMA PARAMETRIC BOOST...
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Page 5: Build Notes
This wafer will act as a You could also use a utility knife or down the lugs. Use a straight-pin pot C-taper pot since it is upside-down. Dremel tool to cut it away. as shown in step 1.) CHROMA PARAMETRIC BOOST... - Page 6 The original SP-1 used the Raytheon RC3403A “ground-sensing” quad op-amp. Raytheon hasn’t manufactured analog components in several decades, and originals are scarce today—but fortunately the New Japan Radio NJM3403A is an exact substitute and still in production. CHROMA PARAMETRIC BOOST...
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Page 7: Schematic
SCHEMATIC 100R 1N5817 100uF 47uF 100n 47pF IC1A NJM3403A 470R IC1B IC1D NJM3403A NJM3403A 100n GAIN IC1C NJM3403A CHROMA PARAMETRIC BOOST... -
Page 8: Drill Template
INCH 0.625” 0.625” ø3/8” ø3/8” ø1/2” SPECTRUM BALANCE x: -0.65, y: +1.71 x: 0.65, y: +1.71 ø9/32” ø9/32” LEVEL x: 0, y: +0.66 ø9/32” CENTER (0,0) FOOTSWITCH x: -0.775, y: -1.20 x: 0, y: -1.20 ø5/16” ø15/32” CHROMA PARAMETRIC BOOST... -
Page 9: Enclosure Layout
ENCLOSURE LAYOUT Enclosure is shown without jacks. See next page for jack layout and wiring. 125B CHROMA PARAMETRIC BOOST... -
Page 10: Wiring Diagram
GND +V +V JACK GND JACK GND GND PCB 125B 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. CHROMA PARAMETRIC BOOST... -
Page 11: Document Revisions
(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. CHROMA PARAMETRIC BOOST...
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