DIY NES RF module and buzzing audio

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Shaytan
Posts: 3
Joined: Tue May 18, 2021 8:38 pm

DIY NES RF module and buzzing audio

Post by Shaytan »

Hi all,

recently i've acquired a NES front loader with a shorted RF modulator, digging the web for some replacement board projects i found this:

http://blog.ampli.fi/nintendo-nes-rf-module-removal/

so I've decided to replicate this board having mostly of the necessary components.
Everything is working correctly apart from the audio output which sounds ok(ish) but with a constant low tone buzz/hum over the original audio.

Is there any way to fix it?

I'm not so expert reading schematics but the audio output should be rather straight forward...but obviously i'm missing something, so any pointing in the right direction would be appreciated, thanks! :)
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: DIY NES RF module and buzzing audio

Post by lidnariq »

They (and you) didn't need the extra two wires for the power switch. The correct names for the pins on the RF modulator are

1) "Video in"
2) "Audio in"
3) "5V to system"
4) "Power from switch to voltage regulator"
5) "Power from jack to switch"

so you could have just shorted pins 3+4, and provided +5V via pin 5

The sound quality is probably due to using a mediocre 5V power supply. You should add a big ol' capacitor onto the replacement for the RF box.
Shaytan
Posts: 3
Joined: Tue May 18, 2021 8:38 pm

Re: DIY NES RF module and buzzing audio

Post by Shaytan »

Thank you for the answer,

I didn't cut the wires going to the blue connector like the author of the article, so i can reverse the changes anytime. I also used dupont cables to make it easier to remove.

So, if I've understood correctly, I can leave the power switch board untouched, bridge pin 3 and 4 together on the NES motherboard and just use one single wire from pin 5 to the positive side of the DC connector of the replacement board.

Regarding the big ol' capacitor to add, the origianl RF box uses a 2200uF cap, can I use the same one?
I'm thinking to put it right before the power jack connector (positve side to 5v and negative to ground), is it correct?

Thanks again :)
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: DIY NES RF module and buzzing audio

Post by lidnariq »

Shaytan wrote: Thu May 20, 2021 3:43 am Regarding the big ol' capacitor to add, the origianl RF box uses a 2200uF cap, can I use the same one?
Maybe. That one's pretty old by now, and if the RF module is broken there's no guarantee it's still working adequately.
I'm thinking to put it right before the power jack connector (positve side to 5v and negative to ground), is it correct?
Yeah, that should be ok.
Shaytan
Posts: 3
Joined: Tue May 18, 2021 8:38 pm

Re: DIY NES RF module and buzzing audio

Post by Shaytan »

lidnariq wrote: Thu May 20, 2021 10:45 am
Shaytan wrote: Thu May 20, 2021 3:43 am Regarding the big ol' capacitor to add, the origianl RF box uses a 2200uF cap, can I use the same one?
Maybe. That one's pretty old by now, and if the RF module is broken there's no guarantee it's still working adequately.
I'm thinking to put it right before the power jack connector (positve side to 5v and negative to ground), is it correct?
Yeah, that should be ok.
Thanks for the advice lidnariq, unfortunately the buzzing is still there :(

I didn't revert the changes to the power board so right now the replacemente board is still connected direcetly to the switch.
Would it be wiser to use pin 5 on the motherboard to provide power to the DIY board or there is anything else i should look at?
lidnariq
Posts: 11432
Joined: Sun Apr 13, 2008 11:12 am

Re: DIY NES RF module and buzzing audio

Post by lidnariq »

60Hz buzz comes from one of two different places in the NES:
1- interference from the PPU
2- Bad power supply

#1 should change "tone color" depending on what's being drawn, with a solid black screen quietest. Even at best, no commercial mainboard ever achieved perfect lack of crosstalk, so I don't know just how bad what you hear right now is.

#2 is probably irrelevant after the added capacitor
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