DIY VCO Part 2: The simplest exponential converter

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Buy as a DIY kit: https://www.ericasynths.lv/shop/diy-k...

UPDATE/PLEASE NOTE: Since learning a bit more about transistors, I've come to realize that the way i differentiate between a transistor's linear region and that "not really on, not really off"-state here is quite bogus. The relation between base voltage and collector-emitter-current is always exponential. This doesn't invalidate the use case, though (obviously), because in the end everything works out. Just keep in mind that my close-up explanation here is wrong!

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 second part is focused on adding CV capabilities to our oscillator core. Topics include NPN transistors, potentiometers and voltage addition. If you want to follow along, here's a bill of materials:

1x BC548C Transistor
1x 4k Resistor
2x 10k Resistors
2x 100k Resistors
1x 100k Potentiometer
1x Audio Jack Socket (to connect your sequencer)

Chapters:
00:00 Intro
00:25 Wave Shape Fix
01:04 Frequency Basics
01:52 Lowering the Pitch
02:30 Resistance or Capacitance?
03:02 Capacitance – Drawbacks
03:30 Resistance – Advantages
04:12 NPN Transistor Basics
07:23 NPN Linear Region
08:48 Linear Region Drawbacks
10:27 V/Oct Basics
11:07 NPN Semi-Active Region
13:03 Installing the Transistor
13:46 Potentiometers
16:08 Potentiometer Setup
17:29 Crude CV Demonstration
18:05 Scaling Basics
19:07 Scaling in Practice
20:00 Offset Basics
20:31 Offset in Practice
20:53 Scaling & Offset combined
21:32 Scaling & Offset in Practice
22:17 Temperature Dependence
22:33 Outro