Try to give due credit to others wherever and whenever you can. If you offer something to the public domain, then do so without expecting any compensation or credit. Everything that you receive in return is a gift.
Stompbox circuits are not protected by copyright and they are rarely, if ever, protected by patents. Images and trade names are protected by copyright. As noted in the Wikipedia article Copyright,
Copyright does not cover ideas and information themselves, only the form or manner in which they are expressed.
Copying other manufacturer’s stompbox circuits has been standard practice in the industry since the beginning. A leading example is the many copies of the Tubescreamer by Ibanez. The copies are not labelled with either “Tubescreamer” or “Ibanez” but in other respects the copies are very similar, if not exact.
Jack Orman gives an explanation in his article Is It Okay to Clone?
Patents protect the circuit designs – copyrights on schematics do not. If there is no patent it is okay to clone, but do not use the name or trademarks of the original on your pedal. If you mention the original pedal name or company as a means of explaining that your pedal is a clone or based on its design, it would be good to include a disclaimer stating that you did not manufacture the original so that it cannot be claimed that you are trying to confuse the consumer or steal their business.
So a circuit design without a patent is in the public domain. Authors’ attempts to impose conditions for use are not binding. Demanding to be paid for application of such circuit ideas is naive. As described in the Wikipedia article Public Domain,
Public domain comprises the body of knowledge and innovation (especially creative works such as writing, art, music, and inventions) in relation to which no person or other legal entity can establish or maintain proprietary interests within a particular legal jurisdiction. …
If an item (“work”) is not in the public domain, it may be the result of a proprietary interest such as a copyright, patent, or other sui generis right. The extent to which members of the public may use or exploit the work is limited to the extent of the proprietary interests in the relevant legal jurisdiction.
Reverse engineering circuits is a form of reading about a circuit idea. In effect, producing and marketing stompbox circuits puts the associated circuit ideas in the public domain.
Manufacturers can certainly discourage attempts to reverse engineer their stompboxes. Various approaches are described by R. G. Keen in his article Dirty Tricks. R. G. concludes
In the end, [dirty tricks do] not protect a manufacturer from someone who will take the time to measure and think, and who also has the background to decide the circuit does or does not make sense from the parts that aren’t faked. … My own personal conclusion is that obscuring the contents of an effect is a costly exercise in doubtful security. I suspect that is why most makers do not use these.
Inventors do not always benefit from their ideas. Some ideas are difficult to exploit for profit even though the ideas are valuable. Claims of being exploited after placing a circuit in the public domain are mistaken. Clearly some people have been hurt and, just as clearly, they are also responsible.
If you design a circuit that might be a successful product then consider selling it to an established manufacturer. Most of the business seems to be marketing, not circuit design.
If you want your circuit ideas to be for your exclusive use then you must find a way to keep them secret. One way is to tell no one. If you want to control how your circuit ideas are used by others, then do not put them in the public domain.