Support the channel... ... through Patreon: https://www.patreon.com/moritzklein ... by buying my DIY kits: https://www.ericasynths.lv/shop/diy-kits-1/ Working simulation on falstad: https://tinyurl.com/ygbk9l6f In this double episode, I’ll walk you through the process of designing a classic transistor-based VCA (voltage controlled amplifier). The goal is to first de-mystify the bipolar junction transistor (BJT), its usage in a common emitter amplifier plus its two central flaws (variations between seemingly identical samples & temperature dependence), before then exploring the differential amplifier (also known as the long-tailed pair) and how we can get it under voltage control. Inverting amp in-depth explanation: https://youtu.be/4r3TTaUKNe0?t=120 AC coupling in-depth explanation: https://youtu.be/FUz3gFAh9pY?t=143 If you want to follow along, here’s a list of components: 2x BC548 NPN transistor (matched) 1x TL072 dual op amp (TL074 works too) 1x 100k potentiometer 2x 470k resistor 1x 200k resistor 3x 100k resistor 1x 33k resistor 3x 10k resistor 1x 1k resistor 1x 100 ohms resistor Chapters: 00:00 Intro & Sound Demo 03:53 Voltage Dividers 09:22 Resistors vs. Transistors 14:12 Common Emitter Amplifier 19:50 Emitter Resistors & Negative Feedback 27:34 Gain Changing & Sketchy VCA 34:20 Diffamp/Long-Tailed Pair 39:11 Voltage Subtraction 43:41 Final Circuit 45:30 Sound Demo & Outro