Is Modular Entropy Multiplication really a new form of entropy?
By doubling the voltage in every step, this circuit essentially amplifies the small amount of noise present in all components.

However, there is no proof of how much of the output is a result of unpredictable noise, as opposed to predictable (in theory) imperfections of the components. So I would treat the claim of 7.9 bits of entropy as unfounded.

The related Inifinite Noise project does such an analysis (including an explanation where the noise comes from), and claims about 6.9 bits of entropy per byte.