Tuesday, September 15, 2015

Solving quirks of the Everdrive expansion sound

As it turned out the expansion audio of the Everdrive has even issues if no expansion audio is available. Take these games for example: Metroid and Akumajou densetsu. Metroid doesn't utilize expansion audio but the latter one uses a VRC6. Both games have in common that the sound is silenced if the game is paused. On metroid you can clearly hear a low pitch static noise. On the VRC6 game you don't. As far as i can assume this might be caused by an undriven output of the FPGA. As the port is not driven the signal is influenced by digital noise from the cart itself.

There is no way to solve that except changing every mapper that is out there.... or is there one?
I did it the following way and it also has another advantage.

I don't like to drill in my NES so I made a small board for this purpose.
Here we have a poti with 50kΩ. The middle pin is connected to the mixing circuit. The other ends to ground and to the expansion audio from the everdrive.
Also there is a switch to disable the expansion entirely having a noise free experience again.

The poti makes it possible to use my 100% volume version of my VRC6 mod and at the same time having an analog way while listening to the music to setup the volume.

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