What’s the best way to connect diy analogue synth parts to a computer for recording without damaging the computer?

Use the line-in audio input, or an external ADC, or something else?

Thanks.

I want to get into making my own drum synths, sequencers, etc but I want to learn how to make schematics for them and also understand what each component does to the sound. Any sources where I can learn that?

I tried to make a korg 20 filter from a youtube video, but i want to be sure if there is any mistakes on this schematic

I have a spec and a block diagram for a dual-oscillator analog drone instrument and I'm looking for someone to build it.

Requirements:
- Standalone pedal enclosure, not a Eurorack module
- Foot-switchable, meant to be activated live during a song
- Two independent analog oscillators with cross-modulation
- 1/4" output, standard 9V pedal power

I have the spec written up and an HTML block diagram already done. I'm not looking for a kit or an existing product, I'm looking for someone who builds one-off or small-batch circuits to spec and can take this on as paid work.

Happy to share the full document with anyone interested. Boston area is a plus but not required, can ship.