Review of a FX-Audio FX03 low cost DAC

The device was bought from Audiophonics, not sponsored by anyone. I am not affiliated with any of the involved brands or companies.

Technical specifications

Output level	2.5 Vrms obviously not correct! 2.00 V, @ ES9028 data sheet, also SGM98000 has 2 Vrms specification, NOT 2,5 V. This is confirmed by measurement (1.989 V)
Output load	not specified (600 Ω min + 200 pF max, @ buffer data sheet)
Output impedance	not specified (22 Ω measured)
Output distortion	0.005% (frequency, level and load not specified)
DAC chip	ES9028Q2M
Audio buffer chip	SGM89000
usb chip	SA9137

PCB

The PCB reveals that the manufacturer utilizes 1202 SMD resistors (1/8 W), which are not appropriate for high quality audio devices They have a considerable thermal modulation. This causes increasing H3 harmonics with increasing output level. There are also ceramic capacitors in the signal path, which are probaly MLCCs. This type of capacitors are not appropriate in the signal path of high quality audio because they modulate their value with the voltage.

Distortions

The specified distortion value is largely maintained, but not always. These measurements are at different levels and 40 pF + 2600 Ω load. Distortions are limited by the audio buffer and the SMD resistors. The audio buffer is specified with 0.001% THD+N and the DAC chip with -120 dB (0.0001%)

However, the output contains a large number of harmonics.

Improved connectors

Cinch connectors are horrible, so i replaced them by SMA connectors.

Summary

This is a low cost, low distortion DAC, good for audio. Not recommended for REW measurements.