Ground Loops

This set of c. 50 slides is the culmination of my experience over a period of about 25 years building numerous power amplifiers and preamplifiers. I first started out in audio about 40 years ago as a teenager. Some of my creations were reasonably quiet – through pure luck – and others hummed and hissed horribly. Later, my skills improved dramatically, and especially so after reading one of Henry Ott’s books back in about 1988/89 whilst developing a very high resolution Digital Panel Indicator for industrial applications at the company I worked for. I then left DIY audio for about 15 years (career, family etc), returning to the subject again about 15 years ago, having forgotten a lot of my practical skills. The path from electromagnetic theory expounded on numerous websites, application notes and posts on various web forums to building quiet amplifiers every time is not easy and requires a bit of practice. The underlying theory can be extremely complex, however, with some effort and focus you can quickly master the basics.  This set of slides focuses on unbalanced interconnects (aka ‘single-ended’) that use the standard RCA phono connectors, since this is where problems mostly arise. 

When it comes to humming and hissing amplifiers, good practical advice is scarce, though often misguided opinions on the subject seem easy to find.

This presentation (which will remain a work in progress and be expanded from time to time) is designed to get audio constructors up and running quickly both in the construction/planning phase, but also debugging. It will hopefully also serve as a useful reference for anyone wanting to know a bit more about EMC.

How to wire up an amplifier_3

(Updated and new material added July 2018)

Here is some additional material

Amplifier PCB Design Guidlines for Minimizing Hum

For some practical examples of low noise amplifiers using these techniques,  see the nx-Amplifier and sx-Amplifier on

The picture below shows the internal wiring of one of the two nx-Amplifiers I built with zero noise or hum problems. The power wiring is tightly bundled, and small signal wiring is kept well away from the transformer and other power wiring. On the PSU PCB, strict attention to the capacitor ‘T’ connection and ‘star’ ground return result in an exceptionally quiet amplifer.