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