DIY VCO Part 1: The analog oscillator core anyone can build

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In this series, I'm taking a detailed look at how to build an analog VCO from scratch, using just a handful of cheap components. It's the basis for any synthesizer. To keep it as beginner-friendly as possible, I'm explaining what all the components do in detail.

This first part deals with the oscillator core, op amp-buffers, AC coupling and voltage dividers. If you want to follow along, here's a bill of materials:

1x Breadboard
2x 9V battery plus clip OR 1x dual 9-15V power supply
1x 40106 IC
1x TL074 IC (you can also use a TL072, we won't be needing more than one op amp)
1x 1N4148 diode
1x 1 uF foil capacitor
1x 2.2 nF foil capacitor
4x 100k resistor
1x 3.5mm OR 6.35mm jack socket
lots of jumper wires

Chapters:
00:00 Intro & Sound Demo
01:18 Electricity & Oscillation Basics
12:13 Materials Overview & Build
16:20 Buffers & Negative Voltage
19:37 Offsets & AC Coupling
23:45 Voltage Dividers
26:39 Listening & Outro