This is the most complex DIY guitar pedal PCB I’ve seen, but the build is well worth the effort. Design, layout and documentation is top-notch, and the quality of the PCB and enclosure are excellent. Thanks to Kevin for his outstanding work on this project.
I used the Aion PCB, enclosure, name plate and parts list, all stock except as noted below. Kevin’s listed sources were all good, even for the hard-to-find 2.5kA pots.
I tried subbing a NE 5534AP for IC1 (the LF356N) but it was not compatible, CH 2 levels fell off and distorted after about 2:00 on the Vol2 knob. I replaced it with an OPA134 in IC1 and that sounded great. I also subbed NJM 2068DD for all the RC 4558P IC’s and the noise floor is very good for a circuit with this amount of gain.
I liked the sound of a cap in place of the CX1 jumper in the Channel 1 tone stack. To my ear CH1 was a little bass-heavy with the jumper, and modeling it with the Duncan Tonestack Calc app showed a nice curve with an 80 to 100nF cap in that position.
I made current-limiting resistor substitutions (RX5-6) based on current calculations for low-current waterclear LEDs, followed by some final adjustments for taste.
I had some higher-voltage-rated 400x diodes on hand with the same forward voltage as the 4004, so I used those on the power input side. I matched the Vf of the symmetrical pairs as closely as possible (D6 with D9, D7 with D8) just for fun.
With a 10.1V AC power supply, measured current draw is:
CH1 active: 365mA with load resistors, 315mA without
CH2 active: 370mA with load resistors, 322mA without
I may swap out the DC jack for one with a 2.5mm center pin to match my pedalboard’s TrueTone CS-12 9VAC supply cable (the DC supply cables are 2.1mm.) I’m not sure whether the Alesis 9VAC power supply has a 2.5mm connector as well, but I’ve ordered one for portability when I’m not using my pedal board.
I set the Distortion trim pot for the recommended 4.4V, and the Compressor trim pot fully CCW which reads about 450mV on output. The recommended 1.17V output for the Comp calibration required the trim pot to be fully CW and needed an excessively high input signal to trigger the compressor.
Again, this is a great project for the experienced builder, and I recommend it highly!
Modifications or part substitutions
IC1: TI OPA134
IC4-IC9, IC12: NJM 2068DD
CX1: 82nF (80 to 100 sounded good)
D1, D2: 1N4006
D4, D5: 1N4448
RX5, RX6: 47k to accommodate bright low-current LEDs for CH1/CH2/Bypass
RX7-RX9: 5M which keep these 3 LEDs barely unlit in the “off” state
Removed load resistors RX3-RX4 after initial testing to reduce current requirement