Stereo mod - which method?

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HunterZ
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Stereo mod - which method?

Post by HunterZ » Thu Feb 19, 2009 1:22 am

I have 2 NES systems (one from eBay, and another that I've owned since the early '90s), so I've decided to do a stereo mod on one of them.

However, I've found two different methods of doing this, so I was wondering if anyone can recommend one over the other.

The first I found here: http://www.raphnet.net/electronique/nes ... php#stereo which is based off of the one here: http://www.disgruntleddesigner.com/chri ... tereo.html

I'm a little bit unsure of the best place to tap the mono audio because each person is using a slightly different spot (and the FC1 guy is pretty vague; even though I found the component - a resistor - it looks like it also goes through at least another capacitor before reaching the pin to the RF module that the other guy used).

The second method is on the ben heck site, here: http://www.benheck.com/Games/Nintendo_p ... Up_NES.htm

That method looks a lot simpler, and I have a 1K dual gang pot salvaged from a broken pair of stereo headphones that just might work perfectly for the mono mixing. However, it taps the faux stereo channels from a different spot and doesn't tap mono sound at all, and it mentions being quieter than the normal mono output.

Does anyone have any opinions on what method to use?
Last edited by HunterZ on Thu Feb 19, 2009 6:24 pm, edited 5 times in total.

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Re: Stereo mod - which method?

Post by Metallica Man X » Thu Feb 19, 2009 3:06 am

I dunno if I'm biased or not, being a long time benheck-er, but I'd go with Ben's Method just cause :)
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HunterZ
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Re: Stereo mod - which method?

Post by HunterZ » Thu Feb 19, 2009 1:50 pm

Additional questions:

- What are the reasons that one method has capacitors added and the other doesn't?

- Can I leave the resistors intact in the Ben Heck method, or will it make things goofy? I'd kind of like to leave the mono output intact for backwards compatibility if possible (although it's not a deal breaker as I have second, unmodified NES).

As a side note, I'm toying with the idea of removing the RF module so that I can use the holes in the case for the stereo mod (old RF hole -> composite, old A/V holes -> stereo audio), but I've heard it can be a pain to remove. I have a soldapult though so maybe that will make it a non-issue.
Last edited by HunterZ on Thu Feb 19, 2009 5:49 pm, edited 2 times in total.

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Re: Stereo mod - which method?

Post by nevermind1534 » Thu Feb 19, 2009 5:45 pm

the raphnet guy based his off of the other one.
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HunterZ
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Re: Stereo mod - which method?

Post by HunterZ » Thu Feb 19, 2009 5:49 pm

Yeah, I just referenced them both for completeness, but I consider them to be basically the same.

Edit:

Saw another thread with this schematic of the default audio output path of the NES:
Image
What is all that circuitry for between the CPU pins and the mono audio output? Some kind of amplifier I guess. Would I get better output by feeding only one pin from the CPU into that circuit and the other into a separate replicated circuit?

It's worth noting that ben heck's method seems to tap the same places in the schematic as the other method even though they're on different physical places on the NES mainboard (opposite sides of the CPU).


Edit: Found a spare Motorola 74HCU04 laying around, so I'm playing with the idea of breadboarding a double amplifier circuit based on the NES schematic just for the heck of it. I'll put a couple of 10K pots on the input end of the breadboard to implement benheck's cross-mixing method. The hard part will be figuring out what I can use for the inductors, because I have no idea how to identify the inductance of any that I may have laying around, nor am I experienced enough to make one of my own. I also can't find the 39uH inductor on the NES itself to use as an example :(

Edit 2: Ah, I didn't know that blue and green resistor-like components can be inductors rather than resistors! The green component FC1 on the mainboard near the RF box is the 39uH inductor in the schematic. ...doesn't help any though, as I don't seem to have any resistor-coded inductors laying around unless I want to gut both NESes :( All I have are some crude bare-winding ones with no way of identifying them, other than something over the top like using a step-down transformer AC power supply to make a crude signal generator. Maybe I'll just do the no-amplifier stereo hack :P

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Re: Stereo mod - which method?

Post by thewizdawg » Tue Feb 24, 2009 10:47 am

Any update on this? I would like to add stereo to my NESp but I've never found any good instructions.

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Re: Stereo mod - which method?

Post by HunterZ » Tue Feb 24, 2009 1:47 pm

Right now I'm fiddling with breadboarding a pair of generic transistor-based preamp circuits to route the sound outputs to.

I'm almost tempted to pick up a 3rd used NES from eBay and gut it for parts to breadboard the NES preamp circuitry for better accuracy, but I'm going to try it this way first because I know I have all the parts laying around.

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Re: Stereo mod - which method?

Post by nevermind1534 » Tue Feb 24, 2009 3:24 pm

HunterZ wrote:Right now I'm fiddling with breadboarding a pair of generic transistor-based preamp circuits to route the sound outputs to.

I'm almost tempted to pick up a 3rd used NES from eBay and gut it for parts to breadboard the NES preamp circuitry for better accuracy, but I'm going to try it this way first because I know I have all the parts laying around.
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HunterZ
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Re: Stereo mod - which method?

Post by HunterZ » Tue Feb 24, 2009 3:53 pm

Well I think I just need the green 39uH resistor-coded inductor (FC1 on the schematic and motherboard I believe). I should have the rest of the parts laying around, provided the transistor used isn't obscure.

Edit: After almost giving up on looking for a pair of 2N3904 transistors and playing with the idea of using a dual opamp IC instead, I finally found one in my breadboarding kit and another on the motherboard of a long-dead 8MHz 286 PC clone from 1987 (I saved the mobo because it's completely covered in logic gate ICs, 32kbit RAM chips, etc. that I thought would be good if I ever decided to do a digital logic project).

Live_Steam_Mad
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Re: Stereo mod - which method?

Post by Live_Steam_Mad » Mon Aug 06, 2012 5:41 pm

Topic revival LOL.

I am just now finishing soldering up my first circuit which is using the whole of the components in the above schematic using the 74HCU04, and am going to try it on my NTSC revision 4 toaster NES. If it works I'll post more.

Cheers,

Alistair G.

HunterZ
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Re: Stereo mod - which method?

Post by HunterZ » Wed Aug 08, 2012 11:22 pm

Live_Steam_Mad wrote:Topic revival LOL.

I am just now finishing soldering up my first circuit which is using the whole of the components in the above schematic using the 74HCU04, and am going to try it on my NTSC revision 4 toaster NES. If it works I'll post more.

Cheers,

Alistair G.
Let me know how it goes. I think that's going to be the best way to do it, because it will keep an authentic NES preamp circuit on each channel.

I ended up giving up on my mod, and the NES I had disassembled is still in pieces 3 years later! I guess it is now just a pile of spare parts for the working one.

Live_Steam_Mad
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Re: Stereo mod - which method?

Post by Live_Steam_Mad » Fri Aug 10, 2012 8:24 pm

YAHEY!! It works... only done 1 circuit so far... Now the "white noise & triangle & sample channel" is AS LOUD as the NES mono sound, I can tell by putting mono from my NES's red audio socket through 1 channel on my HHB CDR 800 CD recorder analog input (sound goes to -6dB peak max when input is at max., meter is 2 segments down from 0dB), and the above single CPU sound channel comes to the same level on it's own when it's being put into the other input on the CD recorder, from the audio out of my new PCB with the 74HCU04N on it.

Now to do the other one.

BTW my NES has the RGB mod already done, see ;-

nfggames.com/forum2/index.php?topic=1592.0

where I show my mod and how I did it.

BTW Here's the other stereo mod. topic ;-

http://forums.benheck.com/viewtopic.php ... 93#p467093

Cheers,

Alistair G.

HunterZ
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Re: Stereo mod - which method?

Post by HunterZ » Sat Aug 11, 2012 10:00 am

I'm surprised you didn't use the already-existing circuit for one of the two channels by removing the mixing resistor.

Live_Steam_Mad
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Re: Stereo mod - which method?

Post by Live_Steam_Mad » Sat Aug 11, 2012 12:15 pm

HunterZ wrote:I'm surprised you didn't use the already-existing circuit for one of the two channels by removing the mixing resistor.
??? the only circuit that I came across before now just mixed non amplified weak CPU audio channels 1 and 2 with amplified mono audio from the RF box. I don't really know what you mean? Since I then followed the Kevtris circuit that is the one from the NES RF box that amplifies the CPU audio, which means I can finally have my TV at a sensible audio level. Otherwise without it, every time I go from another console then back to the NES my ears get blown off LOL.

I am using the exact schematic here (originally from Kevtris i.e. Kevin Horton) ;-

http://forums.benheck.com/viewtopic.php ... 18#p340162" onclick="window.open(this.href);return false;

I copied all the components onto a perf. board and used the same ones as the schematic including the Philips 74HCU04N that I got from http://www.quarndon.co.uk" onclick="window.open(this.href);return false; with a precision IC socket. The Transistor that I used was the 2SC1740 in TO92 package, NPN, hFE about 550, labelled "C1740 E N" (E= Emitter, N=NPN) that I got from http://www.littlediode.com" onclick="window.open(this.href);return false; via Ebay.

It now has the "Triangle wave / Samples / White" Noise channel (only managed to solder up one circuit yet) just as loud as the mono audio.

Best of all I get NO video noise or picture interference or jail bars at all on my 14" TV or IN76 projector, even with the new audio perf. board working. So now audio and video are perfect as they can be made.

Regards,

Alistair G.

HunterZ
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Re: Stereo mod - which method?

Post by HunterZ » Sat Aug 11, 2012 4:19 pm

It sounded like maybe you were building two amplifier circuits (one for each channel) based on the original NES amplifier circuit design, instead of leaving the original one on the board intact to handle one of the two channels and then building a second for the second channel?

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