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PostPosted: Thu Jul 19, 2018 10:22 pm 
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On the original Famicom, you can tap Pins 1 & 2 on the Expansion Port for audio as it comes from the NES's CPU after the pre-amp circuit Nintendo used in the console. This audio then goes to the cartridge port, so you won't hear any expansion audio from these pins.

On the AV Famicom, you can tap Pins 1 & 2 on the Expansion Port for audio after it comes back through the cartridge port. You can hear expansion audio through these pins now. However, since you can hear a very similar signal from the Multi-AV Out, this was not widely known until I tested it recently. Note that the signal that goes to the Multi-AV Out goes through a further amplification stage using the transistor at Q2 compared to the signal available at the Expansion Port. Overall signal is not significantly louder from the Multi-AV Out but it is possible that it can distort FDS sound. I have been told you can remove the transistor and jumper the base to the emitter and remove R7 & R8 as well.

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PostPosted: Sat Jul 21, 2018 11:15 pm 
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I knew that the RF Famicom expansion port has only the internal audio (because I saw the schematics of it), but I did not know that it is different on the AV Famicom; thank you for mentioning it so that now we will know.

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