Does Calvinism make God the "author of sin"?

Most certainly I have with set purpose taken up the case of God and demonstrated with utter clarity that God is not the author of sin. The Secret Providence of God. John Calvin; edited by Paul Helm (Crossway Books, 2010), 92.

And this is the decree of reprobation, which does not at all make God the author of sin (a blasphemous thought!) but rather its fearful, irreproachable, just judge and avenger. Canons of Dort, Article 15: Reprobation.

God from all eternity, did, by the most wise and holy counsel of His own will, freely, and unchangeably ordain whatsoever comes to pass; yet so, as thereby neither is God the author of sin. WCF 3.1.

In my experience, when Calvinists deny that God is the "author of sin", Arminians regard thir denial as nonsensical and sophistical. If God predestined sin, then how can God not be the "author of sin"? 

The source of the problem is that Internet Arminians typically trade on the connotations of "authorship" in popular modern English usage. Needless to say, that's not the linguistic frame of reference for historical theological usage. Calvin wrote in Latin and period French. The canons of Dort were originally written in Latin. Although the Westminster Confession was written in English, it reflects traditional theological usage.

To take a comparison:

L. J. Paetow, The Arts Course at Medieval Universities (Dubuque: Brown Reprint Library, 1910), 53n2, states that in almost all manuscripts from the thirteen century on, we find actor and not auctor in the sense of "author". M. D. Chenu in "Auctor, Actor, Autor," Bulletin de Cange, II, (1927), 81-86, explains that the confusion between "actor" and "actor" was more a problem of etymology and meaning than of orthography or scribal neglect. Auctor (from augeo), originally meant in the broadest sense of the word "He who produces, makes something, a statue, edifice, some kind of work and very particularly a book"; actor (from ago) also designated "he who makes something," in the broadest sense of the word. It was not however applied to the composition of a book, but remained open to mean any human activity. Nevertheless, the meaning actor remained close to the concept of auctor to the extent that confusion existed in manuscript transcriptions of these words. Cynthia Jane Brown, The Shaping of History and Poetry in Late Medieval France (Summa Publications, 1985), 158n3.

If actor was a synonym for auctor, then to deny that God is the "author" of sin means that God is not the agent, viz, God is not the doer or performer of sin. Rather, it's the human agent (or demonic agent) who commits sin. 

In that sense, it's perfectly coherent for Reformed theologians who deny that God is the author of sin–so long as they have a theology of second causes.