Low-Noise Power For Audio And Sensors: Why Switchers Fail (And How To Fix It)

Low-noise power for audio and sensors is one of those problems that only becomes “real” when you stop looking at ripple on a scope and start looking at an FFT: the supply can appear clean, yet your noise floor rises and your front end turns into an antenna for the rest of your system.

In this clip from Elektor Lab Talk #42, Elektor contributor Ton Giesberts breaks down where “mystery noise” actually comes from, including mains-coupled common-mode junk that rides along happily until it finds a sensitive input stage. The practical takeaway is blunt: if your design is a mic preamp, phono stage, or low-level sensor front end, you often need to treat the supply as part of the analog signal chain, not as a generic utility rail.

Where the Noise Really Comes From

The noise that ruins your FFT isn’t always classic switching ripple at the converter’s frequency; it can be common-mode contamination coupled from the mains and the surrounding environment, which then turns into differential noise once it hits imperfect impedances, cable capacitance, and real-world grounding. That’s why “it looks fine on the scope” and “it’s awful in the spectrum” can both be true. Ton Giesberts explains why:
 

What the Common-Mode Filtering Is Actually Doing

Ton shows why common-mode chokes can drop the noise floor dramatically, and why his low-noise dual-rail supply design doesn’t stop at one filter: it deliberately overbuilds the filtering with multiple common-mode stages and heavy additional filtering, because each stage attacks a different part of the coupled-noise story.

Why the Inverting Rail Choice Matters

A key design decision discussed in the clip is the inverting regulator topology for the negative rail. The point is not “because inverting is cool,” but because it can keep op-amp inputs in a safer, more predictable operating region, which matters when you’re trying to prevent subtle supply behavior from turning into measurable (and audible) artifacts.

Low-noise power for audio and sensors comes up everywhere, from preamps to precision instrumentation, so if you’ve ever fought a noise floor you couldn’t explain, this clip is a useful mental reset on what to measure, what to suspect, and what to filter first.