I want to make a circuit that takes a guitar input signal, and then outputs a signal with fundamental and 2nd order harmonic with the same level (or arbitrary levels, I want to amplify the two components at will).
I figured that there are various ways to do this, but I'm trying to do it all analog if possible (since it usually produces more pleasant sounds). Plus there are already commercial digital octave doublers, and the ones that are analog come as ring modulators (they add more components to the signal). The frequency range is 20hz-20khz at worst, the available DC source is 9V.
I'm trying to get the 2nd order harmonic by taking the input signal through a emitter follower stage, biased so the amplification is sufficiently non-linear to produce 2nd order harmonic distortion (and a little 3rd). Then to isolate the 2nd harmonic, I thought of inverting the input through another signal path and then adding the two signals, and hope that the fundamental frequency cancels out. While trying to do this in spice, I realized that I'm going to have to have some kind of AGC so the two signals hace the same component of the fundamental. Designing the AGC has been rather complicated so far. So the idea that i had is getting a little bit complicated.
Any help or new ideas would be appreciated.