How would I calculate the DC Gain for a Chebyshev Type 2 filter? I'm currently working on an implementation of a Chebyshev Type 2 filter but the gain is all over the place when playing around with the order and ripple. I haven't found anything online but (as far as I understand) I need to calculate the DC gain to compensate for gain differences. How would I go about doing that?

I've tried to do s = 0 for my analog prototype which leaves me with just the coefficients b1 / a2 for every biquad. I multiplied all the fractions of the individual biquads together but the result did not help at all, it seems just as random as the gain itself.

Can anyone point me in the right direction?
I suppose that you obtain a transfer function of the desired discrete-time system in the form

$$H(z)=\frac{b_0+b_1z^{-1}+\ldots +b_Nz^{-N}}{1+a_1z^{-1}+\ldots +a_Nz^{-N}}\tag{1}$$

From that transfer function you compute the coefficients of the second-order sections. Before doing that, you can make sure that the DC gain of $(1)$ equals $1$ (which of course only makes sense for a low pass or a band stop filter).

The DC gain of $(1)$ simply equals

$$H(1)=\frac{b_0+b_1+\ldots +b_N}{1+a_1+\dots +a_N}$$

Obviously, the DC gain is independent of the chosen filter type.