Testing a Ground Loop Isolator: How It Works and How to Build Your Own

Here I examine a ground loop isolator purchased on Amazon and verify what it actually does. Through circuit experiments and measurements, I look at how ground loop noise is generated, whether an isolator suppresses it, and how to build a functional one from scratch.

■ Ground Loop Noise Basics
- Internal structure of an isolator and the role of its transformer
- How a noise loop forms between the grounds of two devices
- Experiment injecting noise between GND-A and GND-B
■ Examining the Purchased Unit
- Resistance measurements between terminals
- Inspection of the internal wiring
■ Building an Isolator from Scratch
- PCB from JLCPCB; components from Akizuki and DigiKey
- Rubycon PMLCAP capacitor and an added high-pass filter
- Assembly and enclosure
■ Verification and Measurements
- Audible comparison with and without the isolator
- Waveform observation under 50 Hz and 40 kHz noise
- Noise reduction across frequencies
- Frequency response and phase characteristics of the finished unit

This is aimed at audio engineers, DIY electronics enthusiasts, and anyone troubleshooting humming noise in an audio setup. Watching gives you a clear picture of how ground loop noise travels through a circuit, how much an isolator can actually remove at different frequencies, and what goes into a home-built version.