You can create any waveform simply by superimposing sine waves.
So here's a simple schematic that lets you do exactly that and nothing much more.
There's 20 sliders, each one controling a harmonic frequency of the base frequency played through midi.
Hate to burst your bubble here
But you can't "create any waveform simply by superimposing sine waves" (resynthesis) without also getting the phase
as well as the amplitude. It is only then that you can recreate any waveform. The more harmonics you use, the longer the wave can be.
20 harmonics will not get you very far, if it's resynthesis you're after.
In Sytrus for example, for a clean single-cycle waveform, it uses 256 harmonics, and a wave of 512 samples to load into it.
There's a thread on this, where we attempt to create resynthesis in SM. Search under the key words "harmonic phase".
I can make custom presets in Synthmaker. Post a CROPPED mp3 of the synth sound you want and I can make it.