Use of frequency multipliers for a signal with DC component
The simplest way to do what you describe is to record the signal at one sample rate FS and then play it back at twice the sample rate (2 &times; FS). All of the frequencies (up to FS/2) will be doubled, and the DC component will be the same.

On the other hand, if you want something that does this continuously in real time with fixed latency, then you'll have to make some compromises. Some frequencies will be doubled and some will not. A certain amount of distortion will be introduced.

You'll have to be clearer about your requirements in order to get a more specific answer.