This page describes a method by which you can modify Nintendo's 8-bit consoles, the NES, Famicom, or any compatible system, to produce stereo sound.
How do I do that? Well, in a nutshell, you do it by opening up your Nintendo system and tapping some wires from the CPU.
Is that hard to do? It depends on your expertise with electronics. If you know how to wrap wires, use a screwdriver, and identify basic electronic components, then you can probably do this with ease.
However, I will make it clear right now that any damage that you cause to your NES, yourself, your brothers or sisters, your house, your city block, or your country as a result of inexperience or ineptitude on your part shall be your problem and yours alone. Having said that, I don't see how that could really happen. But...
So, before I do this, I want to know how it sounds. Does it work as you say? Okay, well, I should say that as the NES is a rather old system, it was not intended to be in stereo. Thus, NES games do not make use of stereo effects or anything like that. Here's basically how you can get stereo sound:
The NES has 5 sound channels: 2 pulse wave, 1 triangle wave, 1 white noise, and 1 sample channel. These sounds are generated directly from within the NES' CPU, a modified 6502 processor. From two pins on the CPU come these sound channels, the two pulse channels on one, and the rest on the other. They then get mixed together and go to the Audio jack and RF modulator of the NES. Simply by taking the two channels before they get mixed into one, you can get stereo sound. Hooked up to an amplifier, and listened to on headphones, the effect really does sound pretty neat. This can also be a way to give your NES' audio output a MEGA BASS BOOST!! All is explained below.
The leftmost pin from which you tapped the audio carries a (weak) audio signal from the NES' audio channels 0 and 1. These are both from the square-wave oscillators. In other words, these are most often used as the lead instrument in music. I'd generally make that the left channel. The pin to the right of the leftmost pin carries the audio signal from channels 2, 3, and 4. These are from the triangle-wave oscillator, and the noise channel. These are almost always used as an accompanying melody and for percussion. Any digitized samples will come out of this pin. I have that mapped to the right channel. Now, plug in the power adaptor to your NES, as well as the video plug if you can. Slide a cartridge (one that has good music right as you turn it on (like Journey to Silius =)))into the slot and keep it pressed down with a rubber band if you have to. Turn on the NES and if you can see the game on the screen, try touching one of the wires which you just connected to the two pins, to the center pin of an RCA cable connected to your stereo amplifier. You should hear some sound coming out of this. If you don't then maybe you will have to touch the outer metal ring of the RCA plug to something grounded. What I used for grounding was one of the screwholes on the side of the RF modulator.
After this, you can do pretty much whatever you want to the audio. I'll tell you what I did. First, I connected an Electrolytic Capacitor, rated at 1µf (1 Microfarad) at 50V, to the two new sound lines in order to protect the NES hardware from power surges or shorts. The negative leg of the capacitor goes to the audio pins, and the positive leg goes to the audio out. I highly recommend that you do this too! Next, I bought some gold-plated RCA jacks so I could connect proper RCA cables to the outside of the NES. I drilled two small holes into the back of my NES unit just to the right of the big RF module. Through that I connected the jacks to the outside of the unit, and then the wires to the jacks. That sounded good, but I still wanted to mix the audio so that it wasn't so separated between the two speakers. I bought two 47K Ohm micropotentiometers for the mixing of audio. I tapped regular mono audio from the component labeled "FC1" on the NES circuit board, as it was the final component before the audio went into the RF modulator. I used this mono signal as the line with which to mix each of the stereo channels, because not only did it contain the sound information of the opposite channel for which to mix, but also it contained some sound information for the corresponding channel; this boosts the volume of the (relatively low) stereo channels. Because they are potentiometers, you can now adjust them to provide the degree of mixing that you desire. Take a look at the wiring diagram that I included. It's not a real symbolic diagram, but just an illustration.
Here's an even better trick. You don't want to mix the channels all the way, obviously, because you just did a bunch of work to get them separated. Instead, slowly lower the resistance of each of the pots while you play a game with suitably high bass (I would recommend Solstice or Silius =) ). As you lower the resistance, you should notice that at a point, the bass tones of the mono channel get mixed in before the rest of the tones. With a little bit of tweaking, you can get much-amplified bass sounds from your modified NES. When I play Solstice on my modded NES for instance, I can make the walls of my room vibrate. Ain't that great?
If you try out the modification explained on this page and have some questions, comments, or criticism, then please send me an e-mail!
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