Like the Boss FA-1, this one was made famous by The Edge who incorporated a Korg SDD-3000 digital delay unit in bypass mode into his tone. This circuit faithfully reproduces the bypassed SDD-3000. With only one knob, it’s essentially a booster pedal, but there’s something special that it does to the tone in the process.
This project is a pedal conversion, so it adds a footswitch and LED and puts everything into a 1590B enclosure. In addition, the original unit used switches to control the pre- and post-gain attenuation with fixed resistors, but this version uses pots to allow more variable fine-tuning.
Since the original was a studio rack unit, it incorporated a +/-15V power supply. This gives an enormous amount of headroom and (in theory) it is entirely unnecessary for guitar-level signals. However, some claim that the 15V supply is crucial to the tone, and I’ve never played an original unit so I can’t say they’re wrong!
So, in addition to the default +/-9V charge pump operation, this project optionally allows for the usage of a +/-15V DC converter, which is an expensive component but allows you to use the exact voltage of the original unit while still being powered by a standard 9VDC supply. The unit can operate on either the 9V or 15V bipolar power mode, but only one or the other—you will not be able to easily switch between them.
Here’s a demo video from Ryan Wood testing out the Eclipse: