Routing the audio amp. Since this is going to be made in 500+ QTY of units I decided 4 layer was the way to go as the budget allowed for it. For the layers I will be using the top and bottom side as signals and the two inner planes as the GND and “virtual” GND of the system. Power will be on the bottom layer. Everything is pretty much routed but I need to clean up the traces now.
I have been working on this amplifier for pinball machines. It is a simple 2.1 system with volume control, tone control, sub cutoff, and sub volume. The main lifting is done by a 4 channel TDA7387 which is mainly for low cost car stereos. It can do 41W so it should be plenty powerful for a pinball machine. For opamps I am using the AZ4558C. This is a generic audio opamp in a dual package.
It is a single supply design so easy integration and makes it able to use low cost switcher style power supplies. I run the power though an opamp set to half gain to create a “virtual ground”. This is the middle bias point for all the filtering. After filtering it then gets DC blocked with in series capacitors and shoved into the TDA7387.
After I route this and organize the schematic I will post a link to the files.