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chowder
AV Famicom
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« on: October 08, 2015, 03:52:23 PM »

I realise this is a pretty contentious issue, seeing as everyone thinks their mod is the "right" way, but I don't think it's helpful to have such a complicated solution pinned as the way of doing it.

This circuit is pretty much all you need, I believe it's taken from the amp used in the AV Famicom:



Any additional "tweaks" to improve jailbars could maybe included as optional extras.
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zmaster18
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« Reply #1 on: October 08, 2015, 06:10:36 PM »

This is it. I use the same schematic but I use a 400ohm instead of 300 and 100ohm instead of 110 because I thought the colors were way off. As for tweaks with jailbars, you can only do so much. Lifting the leg of the PPU and adding some caps here and there only seem to help a little. It's totally optional.
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chowder
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« Reply #2 on: October 09, 2015, 08:13:14 AM »

This is it. I use the same schematic but I use a 400ohm instead of 300 and 100ohm instead of 110 because I thought the colors were way off. As for tweaks with jailbars, you can only do so much. Lifting the leg of the PPU and adding some caps here and there only seem to help a little. It's totally optional.

I think the variance seen in resistor/cap values is down to the differences in PCB revisions mainly, but then again I've seen the same revisions with different components (RAM mainly), and even different CPU/PPU revisions.  CPU-07 is my favourite, I have one with revision "G" chips that I've only otherwise seen in VCCI Famicoms.

The plain mod with shielded video/audio cables works great for that console, trace cutting and pin lifting is completely unnecessary in my view.
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Frank_fjs
AV Famicom
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« Reply #3 on: December 10, 2017, 02:50:41 AM »

I've attached a picture of the exact AV circuit used in the AV Famicom. The one in the original post is close but is missing the high frequency filtering capacitor and ferrite bead.

Regarding jailbars, I use a THS7316 to amplify the composite video signal. The attached pic is from a Famicom console with no pins or traces cut, no copper tape, nothing but pin 21 of the PPU attached to my amp. I hooked all this up with test clips, it looks even better with shorter lengths of shielded wire. Picture is a lot clearer and rock solid with no visible jailbars.

Last and final pic is of the AV Famicom video circuit replicated in a PCB I had produced. This is an early prototype version, final version is smaller and includes the ferrite bead.
« Last Edit: December 10, 2017, 06:54:11 AM by Frank_fjs » Logged
Frank_fjs
AV Famicom
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« Reply #4 on: December 11, 2017, 02:32:20 AM »

Thanks man. Sure am.

I will have 2 board versions available, one with the exact AV Famicom circuit and the other with a THS7314/16 amplifier.

Boards have been tweaked a bit since that photo, they're smaller now, have better solder points and will be white.

Aiming for $15 to $20 USD shipped worldwide in a resealable anti-static bag.

Will post on these forums when ready, but probably won't be till January next year.
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krzy
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« Reply #5 on: December 13, 2017, 09:36:43 PM »

I prefer 2 stage amp like in most famiclones, gives best result, also all elements are SMD to minimize sufrace and ground plane for shielding.
Video input should be connected to PPU 21 (if using DIL40 PPU) or proper pin when using Nes-On-Chip famiclone, with as short wire as possible, amplified output should be wired into RCA connector with coaxial shielded cable.

10$ shiped worldwide

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Great Hierophant
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« Reply #6 on: December 15, 2017, 02:37:11 AM »

I've attached a picture of the exact AV circuit used in the AV Famicom. The one in the original post is close but is missing the high frequency filtering capacitor and ferrite bead.

Regarding jailbars, I use a THS7316 to amplify the composite video signal. The attached pic is from a Famicom console with no pins or traces cut, no copper tape, nothing but pin 21 of the PPU attached to my amp. I hooked all this up with test clips, it looks even better with shorter lengths of shielded wire. Picture is a lot clearer and rock solid with no visible jailbars.

Last and final pic is of the AV Famicom video circuit replicated in a PCB I had produced. This is an early prototype version, final version is smaller and includes the ferrite bead.

That looks very neat.  I assume you still lift Pin 21 from its hole.  Do you think you can add another cap and points for audio?  Also, what was the board revision of your Famicom? 
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Frank_fjs
AV Famicom
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« Reply #7 on: December 15, 2017, 04:02:27 AM »

Do you need an audio cap? From my testing you can obtain buffered audio directly from pin 46 of the cartridge connector. Nevertheless, I still tested with various values of caps and never noticed any improvement, in fact sometimes the cap would degrade audio by making it sound 'thin'. Use shielded wire and there is no hum.

I did have an input/output for audio on my original design but later omitted it for reasons described above. It also keeps the board smaller and reduces crosstalk by keeping audio and video separate. Lastly, people hook up audio in different ways, some grab it from the power board and some perform psuedo stereo mods etc so I thought it best to leave audio separate.

I have several Famicoms and never paid much attention to board versions, will need to get back to you on that...

I experimented with a vast range of video circuits. I found the AV Famicom circuit to be the best in terms of brightness and colour balance and sharpness. The twin transistor method shown a few posts above created a blurred and slightly jittery image in my testing. I also experimented with RF chokes to reduce interference and jailbars, and while it worked well to an extent, you lose image sharpness as a consequence.

I found using short lengths of shielded wire the simplest and most effective way of reducing interference and/or jailbars. I don't bother lifting pin 21 of the PPU or using copper tape to shield as it really didn't make a drastic enough difference to warrant the effort.
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krzy
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Posts: 86


« Reply #8 on: December 15, 2017, 06:43:39 PM »

Quote
I assume you still lift Pin 21 from its hole
No need to lift anything. If you dont want the RF signal, just desolder the PNP transistor that's at  the bottom of PPU (PPU's pin 21 is connected to its base and does not go anywhere else). If you want the RF modulated signal to still be available, just make cable connection between PPU pin 21 and the add-on board's video in.

Quote
Also, what was the board revision of your Famicom?
This one was Famicone, but I used to apply this patch for many different Famicons aswell, I really have no idea of their revision names, one had the RF/DC jack PCB connected with the main PCB using transparent tape cable, the other has the whole RF/DC jack PCB shielded with metal and soldered directly to the main board.

Quote
Do you think you can add another cap and points for audio?
What kind of cap are you talking about? few uF series  cap to eliminate DC offset? This one is already present in famicom.
pF/nF parallel cap to GND to eliminate high frequency buzz? I think it is also present.
Just grab audio from one of the pins that connect main board and RF/DC jack board and route it to  RCA jack.

Be advised that the role of this  add-on board is to amplify video signal without ADDING any noises. If the video signal from PPU already has noise (jailbars), it can't help anything, so you must prevent the noise, not try to eliminate it from video signal. Adding any caps/chokes in series/parralel to video signal is NOT good idea. They will act as a lowpass filter, making image more fuzzy.

How to prevent jailbars thent? Add  few uF + 100nF cap between PPU VCC and GND as a energy reservoir. When PPU is rendering signal, it need to have stable supply voltage. Also hundred uF cap at 7805 input might be good idea if there arent any.
Also, all nes-on-chip famiclones probably will have much better video because address/data busses are concentrated inside and signals does not fly all around whole board.
« Last Edit: December 15, 2017, 06:50:15 PM by krzy » Logged
Ludo
Famiclone
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Posts: 3


« Reply #9 on: December 18, 2017, 01:00:52 PM »

I've always used the Jpx72/80s freak diagram/guide. I kinda want to try the AV famicom diagram now!

Anyway, I've made these boards to simplify the process. It has been working well so far


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jpx72
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« Reply #10 on: January 06, 2018, 03:42:56 PM »

This topic and the Ready-made-kits are really great, well done guys, recommended for everybody. This topic sbould be stickied!
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MaarioS
AV Famicom
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Poland Poland
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« Reply #11 on: February 11, 2018, 11:35:55 AM »

I also use the guide provided by jpx72 but I use Famicom AV resistors for video signal provided exactly in the 1st post. What I did personally to mod all Famicoms Classics is that I removed the completely unnecessary TV-GAME switch, hardwired it to GAME and installed an adapter with TRRS audio jack 3.5mm in the same place. I just solder all resistors and caps the old ghetto way on the back of Fami motherboard and it works still perfectly fine. Video + audio from it works like a charm:



If anyone wants to then I can freely redistribute the gerber files so everyone can reproduce it and do the same AV mod. Optionally I can sell the adapter with TRRS jack socket and ship to worldwide if this is still affordable to anyone and I have extra supply of them
« Last Edit: February 11, 2018, 11:46:59 AM by MaarioS » Logged
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