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Project: Chroma (Boss SP-1 Spectrum)

Build description

RESISTORS: Yageo & Xicon brand metal film & no value substitution except for the R7 experiment.

CAPACITORS: HQ Panasonic solid polymers, low ESR electrolytics, CDE silver mica + film caps

OpAmp (Quad): TL074

The effect of this pedal reminds me of my Japanese-made Jackson Spectrum model guitar with an active circuit. Incidentally, the Boss SP-1 is also called the Spectrum model. My guitar also sounds like a wah pedal when a knob is activated and turned. Chroma EQ is very useful for guitar solos that sound like a wah pedal parked in different modes/positions.

I tested R7 with 22K and the wah effect sounded muddy. With a 27K resistor, it was useless. The pedal emitted a blaring computer-like sound even at a low knob setting. I restored the 18K as originally designed by Aion. And, BTW, the dual balance pot mod was very easy to do. Overall, it was an easy build for me.

Aion-designed PCBs are extremely well-thought-of & with simple & clear instructions, making pedal building fun & easy.

Thanks to Kevin for an excellent re-design of this pedal based on the Boss SP-1 Spectrum model.

Please share your build experience on the Chroma EQ. Thanks for reading.

Modifications or part substitutions

The R7 experiment for a variant effect