The Nimbus Dynamic Overdrive is an adaptation of the Maxon OD-820 Overdrive Pro, first released in 2001 as part of Maxon’s Vintage Series alongside the AD-999 Analog Delay, DS-830 Distortion Master, PH-350 Rotary Phaser, and a few others.
Despite the name, the Vintage Series were not reissues of vintage circuits. The pedals in the series were released in the same big-box enclosure style they used in the 1970s, but featuring all-new designs, vintage-inspired with modern improvements.
With its bipolar +/-9V charge pump and dual-pot “gain/blend” control, the Maxon OD-820 Overdrive Pro actually shares a lot of concepts with the Klon Centaur. They are often compared with one another in sound, but it is by no means a clone. The OD-820 is actually a little closer to a Tube Screamer with regard to its clipping diodes and tone control. (Check out this Legendary Tones article from 2004 comparing the OD-820 with the Klon Centaur.)
The OD-820 is the same circuit as the later VOP-9 Vintage Overdrive Pro. The OD-820 has a larger enclosure that matches the other Vintage Series effects while the VOP-9 is housed in the smaller standard Ibanez 9-series enclosure.
Like the DS-830, the OD-820 is a relatively recent addition to Maxon’s lineup. As far as I can tell, it was released in 2001 as part of Maxon’s new “Vintage Series” line of newly-designed analog circuits that retained the spirit of vintage effects from the 70s and 80s. It was intended to be a modern update or “next generation” of Tube Screamer, starting with the tried-and-true formula but adding higher headroom and a clean blend, as well as re-voicing the drive to better balance it with the clean signal.
In 2007, the VOP-9 Vintage Overdrive Pro was released, which was the same circuit as the OD-820 but in the smaller Ibanez-size enclosure—probably an effort to appeal to two different types of people, marketing the same circuit in both a 1970s-style oversized enclosure and a modern (1980s) enclosure.
The OD-820 is often compared to the Klon Centaur, and for good reason: they both run off of 18 volts and they both incorporate a dual pot for the Drive control that gradually fades the circuit from clean to driven. While there are plenty of other differences, not least being the clipping diode setup (The Centaur uses hard-clipping to ground while the OD-820 uses feedback-loop clipping), the OD-820 has been referred to as the “poor man’s Klon”. (Although at a street price of $200, you can’t be all that poor if you can afford it.)
So who copied whom? The answer is either that Maxon copied the Centaur or that the two pedals were developed independently, all depending on when the OD-820 was first released. But I don’t think the Centaur copied Maxon since the Centaur began development in 1990.
See the History section above for my thoughts on this, but I haven’t been able to corroborate that the OD-820 was actually released briefly in the 1990s as they claimed in very early ad copy for the VOP-9. If it was actually developed in the mid-90s, it probably did not rip off the Centaur since the Centaur wasn’t very well-known at that point. But if it was developed in 2001, it absolutely did. The Centaur hadn’t been publicly traced by that point, but the high-level details were well-known—that it had a dual pot for blending and a charge pump for 18V operation. Those are the only similarities in the circuits, and when comparing the schematics, there is no indication that Maxon lifted any circuit fragments directly from the Centaur. Most likely the engineers just heard about the Centaur, thought those concepts sounded interesting, and implemented them in their own way without having to trace or even handle an original Centaur.
My money’s on the latter being the case—that it was developed in 2001 and inspired by the Centaur. Even though the similarities are very high-level, it appears to be too much of a coincidence… plus, the current marketing copy definitely plays off of the Centaur comparisons.