In the Vogons thread related to this board there are several improvements that have been made to this board. The most notable that maintain a non-SMD design where done by @davidmorom here:
https://www.vogons.org/viewtopic.php?p=1120829#p1120829
Based on that (proven & tested) work the suggested improvements to port back to this project are:
Modify the potentiometer layout to fit a common RK097G, which can be easily found on Aliexpress.
Modified the potentiometer connection to the more common way of outputting the signal trough the central tap.
Added 1k resistors on the gain loop of the TEA2025 amplifier. This reduces the gain from 200 (46dB, which is crazy) to 9.5 (19dB), as the original CMS card (the 1k resistors can be seen on pictures of the original card).
A lot of cosmetic changes: moved some components and traces, texts, logo, component labels, etc
And last, but most important of all, added a 78L05 linear regulator to generate a clean +5V rail to feed the SAA1099 output pull-ups and reference current inputs. This completely eliminates the annoying power supply interference, and gives very good sound quality, with the noise level expectable for an almost 40 years old hardware.
In the Vogons thread related to this board there are several improvements that have been made to this board. The most notable that maintain a non-SMD design where done by @davidmorom here: https://www.vogons.org/viewtopic.php?p=1120829#p1120829 Based on that (proven & tested) work the suggested improvements to port back to this project are:
Photo: https://www.vogons.org/download/file.php?id=151252&mode=view Eagle files and gerbers: https://www.vogons.org/download/file.php?id=192366 (Vogons user required for download)