New AV Famicom Audio Mod: NESAMP

With the av famicom my audio balance fix works but it adds audio distortion.  Talking to ace he said the only way he was able to fix the audio in the av famicom was to use the original famicom audio circuit.  I've constructed myself a schematic of the original famicom circuit excluding the microphone connection:



I have all these parts laying around.  I'll wire this up and install it into my av famicom when I get some free time.  This circuit really isn't very complicated to build.  The amp chip used here is the 74hc368.

Interesting approach! Ill be following this.

I built the circuit and it worked great but there was some interference. I came up with a solution using the nesrgb audio circuit instead:

The opamp on the nesrgb doesn't have a very good range so I built yet another circuit using a better opamp and now it sounds perfect. The new circuit is completely designed by Ace.

I took the ace audio design and tweaked it + fixed an issue with it. Here's a picture of the completed circuit:



It sounds perfect with every game. I'll post a video with captured audio shortly.

I've been working closely these last couple of days of viletim and ace.  Viletim was nice enough to send me the nesrgb audio circuit schematic.  Ace and Viletim both had many great suggestions for ways to improve the circuit.  I managed to get the av famicom sounding perfect with the nesrgb circuit so no need for me to assemble my own amp.  Here's how the nesrgb pcb looks with the audio circuit changes applied:





A number of changes were made to the original circuit but luckily it's very doable to the existing run of nesrgb pcbs.  Chances are these changes will be applied to later pcb revisions.  I'll have a video posted hopefully this weekend of how it sounds.

To put in words what was done: a lot of filtering caps were removed and the gain was adjusted.

Added some filtering, now it sounds like a stock toaster and it mixes in famicom cart audio perfectly:

I'm super curious, but so much is hidden. Ever going to do up a schematic of what all you've changed on both boards?

Grambo wrote:

I'm super curious, but so much is hidden. Ever going to do up a schematic of what all you've changed on both boards?

Honestly if I had come up with the entire thing myself I would post the schematic but part of it is designed by viletim so I'll keep mum on that.  Here's the tl072 circuit ace came up with and I adjusted:



This circuit needs a lpf added probably a cap to gnd after the polarized cap will do it.  I abandoned this circuit when the nesrgb one took over.

I've been spending this last week or so working with ace / viletim / tiido and google learning about nes audio circuitry.  The nes audio definitely needs a little low pass filtering otherwise it gets distorted.  Gain is very important an easy way to tweak your gain is to feed the output into famicom pin 45 and test it with castlevania 3 j until the balance is correct.

Using an opamp is much better than the chips nintendo used to amp since opamps are much more noise free. The opamp on the nesrgb is completely free of noise.

Quick demo of the current modified nesrgb audio circuit. This circuit mixes audio from famicom cartridges with audio chips perfectly:

New audio circuit idea that tiido came up with:



I think this one is the best.

Interesting, what are the particularities of this new amp that make it superior?

MaxWar wrote:

Interesting, what are the particularities of this new amp that make it superior?

It uses an opamp which gets rid of all the cpu noise.  I removed all low pass filtering so there's no extra muffle.  Since the nes / famicom are 5v systems using a gain of more than 47k adds distortion and loses audio range, so I reverted the gain back to 47k.  The way this circuit mixes audio from famicom carts with audio chips is completely non-standard since I had to lower the gain therefore I wasn't able to mix audio the regular way.  The system output is mixed with pin 46 with resistors on each line (1-3k) and then the mixed audio goes straight to the audio output pins.

The way the toaster circuit works is the toaster uses a gain of 47k and then uses a transistor amp to further increase the volume. Instead of building a whole extra circuit I just rewired the mixing using a couple of resistors and so far it sounds great with everything I throw at it.

New circuit using an idea tiido came up with combined with some ideas of my own:



This actually sounds better than the f-labo and uses the built in amp circuit of the av famicom. This is an av famicom only mod.

I'd do this in a heartbeat if I had interest in an AV Famicom. Sounds great.

you do not seem to be a big fan of Stereo Famicom Drakon :p

MaxWar wrote:

you do not seem to be a big fan of Stereo Famicom Drakon :p

Yeah not really. Also adding that would have made this mod way more complex. I like to keep stuff simple so it keeps the cost to a minimum.

The filtering has been yet again increased a little because I found that megaman 2 and mario 2 both sounded a little tinny. Here's how it currently sounds after I fixed the filtering level:





I plan on making a castlevania 3 j video next.