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Top Loader NES A/V Mod


MNiceGuy
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Hello everyone,

 

I've recently completed the A/V mod (via the RetroFixes kit) to an NES top-loader. Everything went smoothly except when I was removing the RF box, I forgot to desolder the audio, video, and ground connections to the motherboard (which is why you don't start such projects late at night after a busy day at work).

 

Thankfully I came to my senses before I could do any real damage and desoldered the connections. They were freed but when I removed the RF box I noticed the copper through-holes came out with it. I chose to proceed with the mod anyway and soldered a lead from the RF audio connection (sans its copper through-hole) on the motherboard to a pair of bridged RCA (I don't care for the 'stereo' mod).

 

The system powers up fine and produces clear sound to both speakers. I did notice the top-loader's sound levels are lower than those of a toaster. I hooked up the newly-modded top-loader alongside a toaster via a composite switch box and flipping back and forth the difference in sound levels was apparent. Sound quality seemed similar.

 

QUESTION 1:

I've read that the top-loader does not have amplification on the audio circuit while the toaster does; suggesting my experience is expected behavior. Is that true?

 

QUESTION 2:

For the through-holes I pulled the copper from, did I do any lasting damage? I'm assuming the NES-101 board is only dual-layered and from what I can see, the connections I mention (RF video, audio, ground) are only traced on the bottom layer.

Edited by MNiceGuy
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You can look at schematics and see as much about the lack of sound amps.

 

I know what traces you are talking about, no damage there unless you are planning to reinstall rf..

 

Tim Worthington's kits has an audio amp built into it. Or more specifically it does its own mixing.

 

I drunkenly made a schematic for some circuitry. No idea if it is correct. https://easyeda.com/hotdog6394/Famicom_Sound_Circuitry-2e2ec9ff2a6347768f71d22d1b185006

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You can look at schematics and see as much about the lack of sound amps.

 

I know what traces you are talking about, no damage there unless you are planning to reinstall rf..

 

Tim Worthington's kits has an audio amp built into it. Or more specifically it does its own mixing.

 

I drunkenly made a schematic for some circuitry. No idea if it is correct. https://easyeda.com/hotdog6394/Famicom_Sound_Circuitry-2e2ec9ff2a6347768f71d22d1b185006

 

If my Google-fu is working for me - Tim Worthington is the person behind the NESRGB mod yes? I briefly looked into that but I could not find a source that has the hardware in stock.

 

Concerning the traces, I DID in fact reuse the audio connection the RF used to use. I tried the 'stereo' mod by hooking into two pins on the CPU, running that through RetroFixes PCB, then back to the RCA audio jacks. Neat effect but not something I was interested in for the long run. I am getting audio from the RF audio connection and it's clean - just quiet.

 

Could I run the stereo mod as described above and then simply bridge the left and right channels at the RCA connectors to get mixed mono?

Edited by MNiceGuy
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If my Google-fu is working for me - Tim Worthington is the person behind the NESRGB mod yes? I briefly looked into that but I could not find a source that has the hardware in stock.

 

Concerning the traces, I DID in fact reuse the audio connection the RF used to use. I tried the 'stereo' mod by hooking into two pins on the CPU, running that through RetroFixes PCB, then back to the RCA audio jacks. Neat effect but not something I was interested in for the long run. I am getting audio from the RF audio connection and it's clean - just quiet.

 

Could I run the stereo mod as described above and then simply bridge the left and right channels at the RCA connectors to get mixed mono?

 

Im certain one of these places has one in stock: http://etim.net.au/shop/shop.php?sc_page=105

Not an easy task to install these. Beware.

 

I don't believe that retrofixes board has any audio amplification on it. Looks like two capacitors and two resistors only.

I believe its based on info already out in the ether: https://easyeda.com/hotdog6394/NES_101_COMPOSITE_MOD-4Q2ZXxTRd

I built the above off of this: https://console5.com/wiki/Nintendo_NES-101#A.2FV_Modification

I think more specifically its probably based on the components on the AV Famicom. But missing the Famicom sound circuitry.

 

Simplest solution would be to lower the resistors that mix mono to that RF spot. That or turn your TV volume up (I understand the pain of this). Looks like those resistors are R6 (200 ohms) and R7 (100 ohms). Those mix into a 1uf 50v cap then to an inductor.

So could try lowering 200 to 100 and 100 to 50. or even lower. You could make a parallel resistor to divide it as well.

 

Best solution would be to lift CPU pin 1 and 2 and rebuild the famicom circuity: https://easyeda.com/hotdog6394/Famicom_Sound_Circuitry-2e2ec9ff2a6347768f71d22d1b185006

 

The one that says original. I could design the board for real quick if you want to try it.

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Im certain one of these places has one in stock: http://etim.net.au/shop/shop.php?sc_page=105

Not an easy task to install these. Beware.

 

I don't believe that retrofixes board has any audio amplification on it. Looks like two capacitors and two resistors only.

I believe its based on info already out in the ether: https://easyeda.com/hotdog6394/NES_101_COMPOSITE_MOD-4Q2ZXxTRd

I built the above off of this: https://console5.com/wiki/Nintendo_NES-101#A.2FV_Modification

I think more specifically its probably based on the components on the AV Famicom. But missing the Famicom sound circuitry.

 

Simplest solution would be to lower the resistors that mix mono to that RF spot. That or turn your TV volume up (I understand the pain of this). Looks like those resistors are R6 (200 ohms) and R7 (100 ohms). Those mix into a 1uf 50v cap then to an inductor.

So could try lowering 200 to 100 and 100 to 50. or even lower. You could make a parallel resistor to divide it as well.

 

Best solution would be to lift CPU pin 1 and 2 and rebuild the famicom circuity: https://easyeda.com/hotdog6394/Famicom_Sound_Circuitry-2e2ec9ff2a6347768f71d22d1b185006

 

The one that says original. I could design the board for real quick if you want to try it.

 

Thanks for all the great information!

 

I've done a little more digging and I think I know why the front-loader has a little more amplified sound than the top-loader:

 

The front loader uses a hex inverter, 74HCUO4P, to amplify the sound from the CPU while I 'think' the top-loader lacks this chip. I found a Ben Heck blog where he was experimenting with the fake-stereo mod on a front-loader and noticed the sound output was noticeably quieter. In his case he had bypassed the hex inverter.

 

Taking a 'quick' glance at an image of the top-loader motherboard, I don't see this chip, or one of its alternatives, anywhere. This would seem to go along with the claim that the top-loader's sound is not amplified.

 

Here is a series of posts from someone who worked out the hex inverter's purpose and was able to successfully implement it into the fake-stereo mod http://benheck.com/forums/viewtopic.php?f=2&t=32658

Edited by MNiceGuy
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Thanks for all the great information!

 

I've done a little more digging and I think I know why the front-loader has a little more amplified sound than the top-loader:

 

The front loader uses a hex inverter, 74HCUO4P, to amplify the sound from the CPU while I 'think' the top-loader lacks this chip. I found a Ben Heck blog where he was experimenting with the fake-stereo mod on a front-loader and noticed the sound output was noticeably quieter. In his case he had bypassed the hex inverter.

 

Taking a 'quick' glance at an image of the top-loader motherboard, I don't see this chip, or one of its alternatives, anywhere. This would seem to go along with the claim that the top-loader's sound is not amplified.

 

Here is a series of posts from someone who worked out the hex inverter's purpose and was able to successfully implement it into the fake-stereo mod http://benheck.com/forums/viewtopic.php?f=2&t=32658

 

I think the schematic I posted has two inverters on it with the same electrical values as the one in the famicom. I think it would be simpler to use a 2 channel amp but purest may want the most authentic nes sound by using the inverter. For psuedo-stereo that is.

 

For mono you would only need one amp/inverter.

 

I know i have used the LM386 for audio amplification in many other systems. The ones on ebay have an adjustable pot for volume. You would just need to wire it inline with the mono sound out (that spot near the RF box). There is places to tap 5v and ground around there too.

That's probably the best ready made solution.

 

Ill read up on that page but I think the LM386 would be best for mono: http://www.ebay.com/itm/like/322369176874?chn=ps&dispItem=1

For stereo you would want something like the LM386 but two channel, then i really dont know what to do to mix in expansion with psudeo-stereo. with mono its just a resistor or something at the end.

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I think the schematic I posted has two inverters on it with the same electrical values as the one in the famicom. I think it would be simpler to use a 2 channel amp but purest may want the most authentic nes sound by using the inverter. For psuedo-stereo that is.

 

For mono you would only need one amp/inverter.

 

I know i have used the LM386 for audio amplification in many other systems. The ones on ebay have an adjustable pot for volume. You would just need to wire it inline with the mono sound out (that spot near the RF box). There is places to tap 5v and ground around there too.

That's probably the best ready made solution.

 

Ill read up on that page but I think the LM386 would be best for mono: http://www.ebay.com/itm/like/322369176874?chn=ps&dispItem=1

For stereo you would want something like the LM386 but two channel, then i really dont know what to do to mix in expansion with psudeo-stereo. with mono its just a resistor or something at the end.

 

I'll definitely check that out. I did find some information where someone basically replicated the front-loaders circuit to get the sound amplified properly but that might be a little beyond my skill/ambition level. If the LM386 just needs 5V, GND, and the audio signal that might just be the ticket.

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