> Well there are the fourteenth
The only bit in the 14th that explicitly addresses voting doesn't establish a right to vote. It says that if the states deny the right to vote to some male citizens above a certain age, then their representation in Congress is proportionally reduced. Note that this mechanism implies that the states can, nevertheless, opt into such an arrangement. So, if anything, it establishes that there's no right to vote.
If you're referring to the Equal Protection Clause. It does not explicitly establish a right to vote, either. It has some effects on voting rights - in particular, it was used to restrict poll taxes in state elections (since the 24th only applied to federal elections). However, the relevant court decisions explained that it was not because it infringed on some inherent right to vote that all citizens possess, but rather because it was unduly discriminatory (on the basis of "the affluence of the voter or payment of any fee").
> and fifteenth amendments
That one says you can't deny the right to vote based on race. Similarly, 19th amendment does the same wrt gender, and 26th does the same wrt age for those 18+.
However, none of these establish a right to vote, per se. For example, if a state denies the right to vote on the grounds that are not related to race, they are not in violation of the 15th.
> and the voting rights act of 1965
That one is more of an implementation of the above, although it goes further wrt placing the burden of proof on the states in many cases.
But, in any case, it's just a law, and as such it cannot establish a fundamental right (since Congress can overturn it at any time).
> those have all been significantly weakened by the judiciary
Given that Harper v. Virginia State Board of Elections was one of the massive expansions of the right to vote, I don't think that's a reasonable assertion. Courts have given, and courts have taken away. If Constitution were explicit on this subject, we wouldn't have this back-and-forth.
> allow permanent disenfranchisement of convicted felons, which seems explicitly against the text of the fifteenth amendment.
Convicted felons are not a race. Yes, there is a racial disparity when it comes to such laws in practice; but the amendment doesn't prohibit any restrictions that result in a racial disparity - only those that are specifically using race as a basis.
Voting Rights Act, as amended in 1982, is the law that prohibits restrictions on the basis of their results, rather than their intent. But even with VRA, a mere disproportionality is not sufficient to declare a restriction unlawful. And, of course, it's still just a law, and therefore cannot provide any fundamental guarantees like the Constitution does.
So, in practice, there's no universal constitutional right to vote for citizens in the United States on the federal level. There's a patchwork of protections, but even when taken in combination, it does not amount to such a right.