I have been interested in testing the differences in loudness between the various revisions of the NES CPU. The conventional wisdom is that earlier Famicoms' internal sound is louder than the later Famicoms or the AV Famicom. I decided to compare the output of my Famicom and AV Famicom. However, the default audio output of the Famicom is through the RF modulator while the AV Famicom outputs an untouched audio signal.
The CPU in my Famicom is a Revision E and the board is a common HVC-CPU-07, the CPU in my AV Famicom is a Revision H (laser etched) and the board is an HVCN-CPU-02. In order to control for all variables, I decided to tap the audio from the Famicom Expansion Port. The port is very convenient because Pin 1 is Ground and Pin 2 is Sound Out. The port only carries internal audio, you won't hear cartridge expansion audio from it. As far as I can tell, the audio mixing and amplification circuitry is identical on all Famicoms and AV Famicoms at the point they are passed to the Famicom Expansion Port, but I could be proven wrong. I know at least there are two 100Ohm, a 20K, a 12K and a 1uF 50V cap common to all Nintendo consoles and they all pass their audio through an inverter.
I recorded the opening tune from Metroid running on my Famicom and AV Famicom. I made sure to record at the same session and at the same volume level (50%) from my PC's line input. Here are my recordings, preserved in the best quality :http://www.mediafire.com/file/gm71kdx93 ... etfam.flachttp://www.mediafire.com/file/d2cocqxqm ... famav.flac
It turned out that there was no real appreciable difference in the volume whether I recorded from the Famicom Expansion Port or the Multi-Out of the AV Famicom. At the volume level I recorded at, there was an audible noise floor from the Famicom that was not present on the AV Famicom. The Famicom is noticeably louder, perhaps by 4.5db. This means that expansion audio in cartridges will sound quieter on an older Famicom compared to an AV Famicom.
However, I also made a recording of Metroid's opening on my front loader NES, which has a Revision G CPU, through its RCA Audio Output connector. The volume was lower than either Famicom, which suggests that I should really try to record a later Famicom with a Revision G CPU (The VCI marked Famicoms with the RF board soldered to the main PCB). http://www.mediafire.com/file/da9i8or9k ... etnes.flac
I don't know why the NES is quieter than the AV Famicom, but I note there seems to be a lot more going on with the NES audio's output than the AV Famicom's. I suspect that if I tapped the audio at the NES Expansion Port, I would have louder audio, but I don't have an ENIO board and I don't have another spare cable to sacrifice by soldering it to the pins.