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 signature all over the analogue output. This project addresses that directly: rather than accepting the baseline noise floor, the internal power rails are reworked so that the generator behaves more like a laboratory instrument and less like a hobby board with a plug-in adaptor.

The work covers identifying where switching noise enters 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 that 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 modification like this is worthwhile or merely placebo engineering.

For a buyer, the practical conclusion concerns expectations. The FY6900 offers a great deal 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. For digital timing, sweeps or rough signal injection, the stock unit is adequate. For use near sensitive analogue circuits or feeding a spectrum analyser, the supply noise becomes the limiting factor, and these modifications are a low cost way to recover 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.