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Author Topic: Fixing the audio problem on the AV Famicom and later released original Famicoms  (Read 11255 times)
Hamburglar
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« on: March 01, 2012, 04:18:17 AM »

I've read about how the audio on the AV Famicom as well as the later released original Famicom were weaker, never really noticed how bad it was until I received an older Famicom a few days ago.

The difference is very noticeable, it appears to me that the AV Famicom and later release Famicom output  their audio lower than the earlier units, and as a result when you play a game what mixes it's own audio with the audio coming from the system, the audio from the system is very faint.


I was looking at a original Famicom schematic, and compared it to the circuit on the AV Famicom and couldn't find where the audio is lowered, I stopped after a while because the PCB is multi layer and very difficult to trace.

The 2 audio channels coming out of the CPU each go to a couple 100 ohm resistors to ground, then one channel goes through a 12K resistor and the other through a 20K and are then combined. So both systems are similar there.

I decided to change the 12K and 20K resistors to lower values to see if that would help, first I piggy backed a 12K on top of the 12K and a 20K to the 20K so then that changed the value to 6K and 10K since they are in parallel. Sound was better but still not great, I then removed the 12K and 20K resistors and put 4K and 3K on there because I do not have anything better at the moment, the sound is greatly improved, Akumajo Densetsu sounds great, I can hear channels I could not hear before.

This is only a temporary fix, when I get motivated enough I'll trace the circuit and find out what is making the audio lower, if anyone wants to try it on their AV Famicom, you should replace the 20K resistor with a 5K resistor and replace the 12K resistor with a 3K, I temporarily connected a 2PDT switch so I can hear the difference with the flick of a switch.

To those of you with AV Famicom units and Akumajo Densetsu, you can hear what I am talking about by going in to the sound menu (hold A then press start) listen to DEMON SEED you should be able to hear a faint drumbeat type sound that is barely noticeable, on my earlier Famicom it is much louder.




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untinip
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« Reply #1 on: March 01, 2012, 05:09:24 AM »

Interesting! I've also read about the audio mixing differences between the original Famicom and the AV Famicom. Could you post a recording of the original Famicom vs. an unmodded AV Famicom vs. a modded AV Famicom? That would be great!
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Hamburglar
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« Reply #2 on: March 01, 2012, 07:43:40 AM »

Still working on it, but here are some WAV files.


AV Famicom original
http://www.mediafire.com/download.php?w383uhvywd4j4a2


AV Famicom Modded
http://www.mediafire.com/download.php?ze52vwq8d8rt4qo


Original early Famicom
http://www.mediafire.com/download.php?ky2f24jz6m0bitn

The original Famicom is still louder than the modded AV Famicom, the "drums" sound very weak on the AV Famicom.
Also the original Famicom is very noisy when hooked up to the computer, unlike the AV Famicom.
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untinip
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« Reply #3 on: March 01, 2012, 08:00:49 AM »

Wow! Amazing work! Your modded AV Famicom sounds almost like the original Famicom! With a bit of fine tuning I'm sure the AV Famicom can be made to sound exactly like the original. I will definitively try this mod when I have some free time!

Nice RGB-mod, by the way. I got to get my hands on one of those PPUs! Wink
May I ask what amplifier you are using to boost the RGB-output signals?
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Drakon
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« Reply #4 on: March 02, 2012, 02:30:03 AM »

Huh that's pretty cool.  Here's a recording of akumajyo densetsu using the av famicom kit I bought from japan.  Akumayjo densetsu sounds 100x better with this kit than when I used the default circuit

http://www.youtube.com/watch?v=BN0lQf02dDY&feature=channel_video_title

untinip he's using the ths7314 amp
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Hamburglar
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« Reply #5 on: March 02, 2012, 02:46:04 AM »

Where does the kit take the audio from? Do you have a recording of the same song?
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Drakon
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« Reply #6 on: March 02, 2012, 02:57:31 AM »

Where does the kit take the audio from? Do you have a recording of the same song?

The kit takes audio directly from the two cpu pins.  The kit also requires you to cut the traces to pins 45 and 46 of the cartridge connector (system audio in / mixed audio out pins) and then you wire those pins into the kit as well.  It's a great kit I've never found an audio circuit that sounds better and it mixes in the audio from famicom carts with audio chips PERFECTLY.  The only weakness of this kit is that it filters out some of the popping drums in tmnt 2 the arcade game and kirbys adventure.  Luckily no other games are effected so I just installed a switch to switch between the kit audio and default system audio for those two games.

Here's an old recording with the same song played through one of these kits

http://www.youtube.com/watch?v=RLGo_P-MNG4&feature=channel_video_title


your circuit sounds pretty awesome too.
« Last Edit: March 02, 2012, 03:08:07 AM by Drakon » Logged

untinip
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« Reply #7 on: March 02, 2012, 05:39:21 AM »

May I ask were you order those kits from?
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Hamburglar
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« Reply #8 on: March 02, 2012, 05:51:09 AM »

That makes sense, that's the only way I thought it could fix the low volume issue, it's bypassing the AV Famicom audio path.  So this kit outputs simulated stereo right? What I am trying to achieve is keep the audio mono and normalize the audio. I was thinking about bypassing the internal audio circuit as well, might not be much of a problem considering that one does not have to deal with mixing the microphone input and the output to RF.

Post Merge: March 02, 2012, 06:03:40 AM
Also, the simulated stereo sounds pretty neat, I wish there was a way to switch between normal audio and the enhanced audio, don't want to attach switches to my AV Famicom, the original Famicom has the TV/Game switch which would be ideal, but I like using my AV Famicom more...
« Last Edit: March 02, 2012, 06:03:40 AM by Hamburglar » Logged
Drakon
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« Reply #9 on: March 02, 2012, 10:35:59 AM »

That makes sense, that's the only way I thought it could fix the low volume issue, it's bypassing the AV Famicom audio path.  So this kit outputs simulated stereo right? What I am trying to achieve is keep the audio mono and normalize the audio. I was thinking about bypassing the internal audio circuit as well, might not be much of a problem considering that one does not have to deal with mixing the microphone input and the output to RF.

Post Merge: March 02, 2012, 06:03:40 AM
Also, the simulated stereo sounds pretty neat, I wish there was a way to switch between normal audio and the enhanced audio, don't want to attach switches to my AV Famicom, the original Famicom has the TV/Game switch which would be ideal, but I like using my AV Famicom more...

I installed a switch in the back but it was a tight fit.  Unfortunately there's no switches on the av famicom so I just found the best place to install one.  If I don't want the stereo effect I set my amp to mono mode and everything returns to mono
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famifan
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« Reply #10 on: March 02, 2012, 04:17:57 PM »

The kit takes audio directly from the two cpu pins.  The kit also requires you to cut the traces to pins 45 and 46 of the cartridge connector (system audio in / mixed audio out pins) and then you wire those pins into the kit as well.  It's a great kit I've never found an audio circuit that sounds better and it mixes in the audio from famicom carts with audio chips PERFECTLY.  The only weakness of this kit is that it filters out some of the popping drums in tmnt 2 the arcade game and kirbys adventure.  Luckily no other games are effected so I just installed a switch to switch between the kit audio and default system audio for those two games.
schematic please!
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Drakon
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« Reply #11 on: March 02, 2012, 07:17:41 PM »

I'm guessing you've never bought a "kit" before otherwise you'd realize that they don't come with schematics.  Here's where I ordered it from:

http://homepage3.nifty.com/F-LABO/ProductsList.html

In other news I wired up one of these audio circuits to the nes 2 top loader and it didn't sound right.  I checked the audio circuit and sure enough it was completely different from other models.  I disconnected a1 and a2 from the existing circuit, wired two 100 ohm resistors to ground and 32kohm between the two and wired it into the kit and now it sounds just like my av famicom when it's wired into the kit.

I also discovered the powerpak doesn't work on the nes 2 *grumble*

*edit* scratch that I fixed it
« Last Edit: March 02, 2012, 07:28:14 PM by Drakon » Logged

Hamburglar
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« Reply #12 on: March 02, 2012, 08:24:32 PM »

I'd be interested in nice clear shots of the PCB and components, I'm curious to see what they used.
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Drakon
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« Reply #13 on: March 02, 2012, 11:02:50 PM »

I'd be interested in nice clear shots of the PCB and components, I'm curious to see what they used.

Fair enough atleast you're not asking for a schematic.  Two njm 2132s, a virtual ground (transistor style), two inductors before the outputs, and the rest is just caps and resistors.  I'm not about to be bothered figuring out the circuit.  Also you can solder in a cxa2075 and get a better image than the cxa1645 that comes with the kit.

Also I did more testing with the audio upgrade kit wired into the nes 2 with the recreated audio circuit (two 100 ohm resistors to ground and then 32k ohms connecting the two channels).  It doesn't sound quite the same as the av famicom, I wonder if it's because I used 1/4 watt resistors instead of 1/8 watt.









« Last Edit: March 02, 2012, 11:08:09 PM by Drakon » Logged

famifan
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« Reply #14 on: March 03, 2012, 05:06:10 AM »

really thanks, Drakon!
i will recreate the sound circuit schematic when i have enough free time.

^_^
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