What Happens Inside a BAE 1073 as You Increase the Gain?

In this video we step away from subjective listening tests and examine the behaviour of a classic Neve-style microphone preamplifier from an engineering perspective. Using a BAE 1073, Logic Pro and Room EQ Wizard (REW), we progressively increase the microphone preamp gain while feeding it a pure sine wave. As the gain increases, we observe: When harmonic distortion first appears. How harmonics develop in the frequency spectrum. The transition from linear amplification into saturation. How the waveform gradually changes from a sine wave towards a square wave. The relationship between waveform shape and harmonic content. This experiment is designed to visualise what is happening electrically inside a transformer-coupled Class-A microphone preamplifier as it is driven beyond its linear operating region. Rather than asking whether one preamp “sounds better” than another, the goal is to understand how and when analogue circuitry begins to alter the signal. This video forms part of our ongoing series analysing microphone preamps through measurement, engineering and controlled experiments. Warning: This video contains loud test signals and high-level audio transients. Please reduce your playback volume before watching. 00:00 Introduction 01:04 Know the Scarlett 2i2 02:14 Scarlett 2i2 vs Apollo X8 Specs 02:58 Objective of the Video 04:16 Warning! Loud Audio 04:31 Harmonic generation at 1kHz Sine Wave 07:34 Wave Form analysis using REW's Oscilloscope If you enjoy evidence-based audio engineering content, consider subscribing for more investigations into microphone preamps, analogue equipment, converters, guitar amplifiers and recording technology. At Skylabs FX, our profile business is built on the same principles: engineering precision, scientific curiosity, and a relentless pursuit of great guitar tone. Visit our website at https://www.skylabsfx.com