Expansion audio not mixing on NES with RGB

[prince tomato]

Hi folks,

i installed an NESRGB board in a frontloader NES,
and added a Famicom cart slot.
it all works fine, except expansion audio is not mixed in.
when playing Otocky from FDS ram adapter with FDS stick i hear only background music from the nes audio out,
and the "shooting" musical sound effects are audible from famicom pin 46, but not mixed in with internal audio.
CPU pins 1 and 2 are connected to the A and B pads on the NESRGB board,
the resistor between pins 3 and 9 on the expansion port is installed, and there is continuity between Famicom pin 46, NES pin 54, and exp. port pin 9,
and there is a 10k resistor between Famicom pin 45 and 46.
i do hear the exp. audio (and nothing else) when i connect an audio output to Famicom pin 46,
but if i connect this signal to the NESRGB mixing pads i get nothing.
could it be the CPU crapped out and is not mixing in the expansion audio?
any other connections i should check?
can i mix in exp. audio externally?
any hints or tips are more than welcome.

[Frank_fjs]

Maybe the 10K res between pins 45 and 46 is too high?

[prince tomato]

Maybe the 10K res between pins 45 and 46 is too high?

i can try to solder in a lower value.
but i doubt that is the problem.
i have no idea about the NES audio mixing circuitry,
so i'm not sure where the exp.audio signal is supposed to go in order to mix with the rest of the audio.
also, i don't know if pin 46 is supposed to output ONLY exp.audio, or both internal audio mixed with exp. audio.

[Frank_fjs]

I'm more familiar with the Famicom than Nes, I can tell you on a Famicom...

Pin 46 is normal/expansion audio combined

Cpu pins 1 and 2 is normal audio divided up between different channels.

Seems like you've done everything correctly. Perhaps there's another step required on the RGB board. Isn't there a pot to mix audio, does that need adjusting? I know the Famicom version of the RGB board provides a new power board which contains the audio circuitry, does the Nes version even support expansion audio?

[prince tomato]

I'm more familiar with the Famicom than Nes, I can tell you on a Famicom...

Pin 46 is normal/expansion audio combined

Cpu pins 1 and 2 is normal audio divided up between different channels.

Seems like you've done everything correctly. Perhaps there's another step required on the RGB board. Isn't there a pot to mix audio, does that need adjusting? I know the Famicom version of the RGB board provides a new power board which contains the audio circuitry, does the Nes version even support expansion audio?

same here, this is my first NES mod.
so, maybe i should feed the mixed internal audio from the nesrgb board into famicom pin 45, and take the combined audio output from pin 45 as audio out?
Tim's RGB board does not have a pot for mixing audio,
it takes audio from CPU pins 1 and 2 and mixes those.
from there it is put out on a single mono output.
and it works great, except it is missing exp.audio,
both from the nesrgb board and the original mono audio output of the console.
Post Merge: February 05, 2018, 11:56:54 pm
ps: i've looked for thungs i may have overlooked like jumperpads on the NESRGB board but as far as i can see,
it doesn't look like there is anything like jumperpads needed for the onboard audio mixing.

[Frank_fjs]

Well the CPU pins 1 and 2 never output expansion audio in any circumstance on any console. This is something a lot of people who 'stereo' mod overlook.

What I don't understand is you have expansion audio coming from pin 46, but when you route this to the RGB board you don't hear this audio. Makes no sense. Is the volume output from pin 46 similar to what the RGB board is outputting from CPU pins 1 and 2? Wondering if the expansion audio is indeed present but not audible/being drowned out by the regular audio. Did you test at a loud volume?

[prince tomato]

the nesrgb board has only 2 pads for adding audio,
1 for each CPU pin,
i tried adding the signal from pin 46 to each of the pads, (cpu pins still attached)
but that only resulted in the music notbeing audible either,
i.e, losing more channels.

i have had the audio from pin 46 hooked up to another tv,
( again, it only puts out the expansion audio, not the complete mixed signal)
, but it sounds crystal clear and has good volume.

[xIceMan]

Did you wire the cable for expansion sound correctly when installing NESRGB?
Pictures please.

This is how you add in expansion sound for the NESRGB (See attachment).

It is in German but it should give you an overview how its done.

[prince tomato]

i don't have that wire from exp. pin 9 to those 2 resistors,
that has to be the issue then.
i've been searching for 3 days now, and this is the first time this is mentioned 
i am going to try this tomorrow,
thank all of you very much for your time and patience

[xIceMan]

Pretty sure it is. Good luck. Let me know how it went!

P.S. If you're interested and want the palettes to be able to be changed via controller. I have an additional board for that so there's no need for a manual switch. PM me if interested.

[prince tomato]

Pretty sure it is. Good luck. Let me know how it went!

P.S. If you're interested and want the palettes to be able to be changed via controller. I have an additional board for that so there's no need for a manual switch. PM me if interested.

that did fix it! 
sounds great too,
following your lead i stumbled upon this:
https://shmups.system11.org/viewtopic.php?f=6&t=47617&start=660
and followed that method.
Otocky sounds great now!

i already installed a round rocker switch in the right side of the NES's bottom shell,
personally i think it looks great, and works a treat.
i am not at all concerned with having it look original,
in fact, i quite like the Frankenstein look.

thanks again for helping out, i sure would not have figured it out by myself.
things like this are so much easier on a Fami than on an NES, but i am really happy with how this came out eventually.
also, this mod is using the Famicom connector to NES and vice versa board that fellow member KRZY designed,
not only does it work like a charm, it made mounting the connectors in the top shell of the NES really easy.
i glued a reinforcing plate of polycarbonate to the inside of the top half of the NES, and dremeled out the space for the connectors,
screwed everything down, and she is good to go.
i'm sure it could be mounted straight onto the NES top without it, but it was only a little effort, and i think the result is much sturdier.

[xIceMan]

Very nice, glad to hear!

I like how you intalled those connectors on top. When I did my Famicom mod to the NES I had a big hole in there not knowing how to close it.
Then again my connectors weren't as low inside as yours. Great job regardless!