SDG #120 FY6900 Signal Generator Power Supply Modifications

The FeelTech FY6900 is a popular budget arbitrary waveform generator, but like most of the FeelElec family it ships with a cheap internal switch mode supply that leaves its fingerprints all over the analogue output. This project tackles that directly: rather than accepting the baseline noise floor, the internal power rails are reworked so the generator behaves more like a lab instrument and less like a hobby board with a wall wart bolted on.

The work covers identifying where switching hash is entering the signal path, improving decoupling and filtering on the supply rails, and reconsidering grounding and return paths on the mains input side. Measurements are taken with a differential probe so the actual supply ripple and the coupled noise on the generator output can be compared before and after modification, which is the only honest way to judge whether a mod like this is worth the effort or just placebo engineering.

For a buyer, the practical takeaway is about expectations. The FY6900 offers a lot of specification for the money, including two channels, decent frequency coverage and arbitrary waveform capability, but the analogue front end and power design are where the corners were cut. If your use case is digital timing, sweeps, or rough signal injection, the stock unit is fine. If you intend to use it near sensitive analogue circuits or feed it into a spectrum analyser, the supply noise becomes the limiting factor, and these modifications are a low cost way to reclaim performance the hardware is otherwise capable of. It is also a useful case study in how much a poor supply can degrade an otherwise competent instrument.