Chroma Equalizer / Boss SP-1 Spectrum DIY PCB Project

Chroma - Boss SP-1 Spectrum Guitar Pedal PCB



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Project overview

The Chroma Equalizer project is a clone of the BOSS SP-1 Spectrum, one of the three original BOSS compact stomp boxes released in 1977. (The other two were the OD-1 OverDrive, which is available as my Corona project, and the PH-1 Phaser.) It was discontinued in 1981, and due to its extreme rarity, it routinely sells for $500 or more on eBay.

The SP-1 Spectrum is a parametric equalizer with only two knobs. The frequency knob sets the boosted frequency between 500Hz and 5 kHz, and the balance (or mix) knob adjusts the dry-to-wet signal ratio. The gain and Q (frequency width) are fixed. It only boosts frequencies—it doesn’t have the ability to cut. Its function is very similar to a fixed wah, and you would hear a wah-like effect if you turn the Spectrum knob while a signal is being passed.