Famicom av mod instructions?

[jpx72]

I don't understand the technical stuff behind it but without the capacitor on sound output I wasn't able to get the sound from Famicom when connecting directly to a "line-in" of a sound card of my computer. There was a strong buzzing sound instead. Something about galvanic separation or something...

[keropi]

maybe it's because the output volume is too high? on my lcd set I have to put the volume to 1to8/100 , anything higher is just too much!

[2A03]

I found that tapping the audio directly from the cart port gives you muffled sound, so I had the audio come from a resistor connected to pin 46

Yep, there's some kind of resistor (or at least what looks like a resistor) labeled "FC1" directly connected to pin 46 and tapping the audio there provides a nice and clean signal. This is just on the HVC-CPU-GPM-02, I don't think it's present on any older revisions.

[MaxWar]

Ok, about the Capacitor on audio output ( Connector pin 46) question, i did some experiments.

I made 4 recordings of Castlevania III intro.
A. without any cap
B. 220 uf cap with + on pin46
C. 1 uf cap with + on pin46
D. 1 uf cap with - on pin46

All recordings are made  with the same parameters.
There is quite an audible difference you will see.   
I will tell you right now that background noise seems to vary seemingly at random ( my experimental setup is a bit dodgy and i do get some interferences) but the level do not seem to depend on what capacitor was used.  If you go at the end of each recording i left some ( silence) with only the background noise. This noise is caused by the famicom as it disappears if i remove power. I expect it would be much less if i used shielded cables and the mod was made with shorter wires. 

Here are the files.
http://www.2shared.com/file/XQLkgomH/FamicomCas3-Capacitor-soundtes.html

[jpx72]

maybe it's because the output volume is too high? on my lcd set I have to put the volume to 1to8/100 , anything higher is just too much!

No this is not the problem, try it yourself - connect the audio without cap directly to PC audio card.

[MaxWar]

With 1uF you will have little bit less bass, it's obvious. Usually "sound" capacitor is 10-22uF. "Background noise" also can come from 2nd pad cable and mic. If you want pure 2A03 sound, you have to rebuild most of audio circuitry. Or at least remove sound line from mic. As about sound files - with no cap, normalized(?), so can not be compared with others. Wrong polarity will destroy capacitor, but not immediately. Ummm, what else you can do - add big ceramic capacitor to each microchip and 100-220uF capacitor in parallel. Do proper shielding, include shielding CPU(like PPU, but from pin1-40)

P.S. audiophilia and 8 bit sound

Yes I am an audiophile and I like 8 bit and 16 bit tunes alot.

As for the Normalized file, i did this for proper comparison. Usually I always Normalize all my audio recordings but when i recorded with capacitor in the line, i had gotten proper volume on first try. ( Full amplitude without clipping ) So i exceptionally did not normalize them. Without Capacitor, the sound was lower and very heavily cut in the bass. In fact it sounded like it was out of a telephone...  This is why i normalize it, to bring the volume back toward the level of the other recordings.  This is in fact to allow them to be more properly compared.

The sound without a capacitor on is very bad. I cannot say exactly why as i do not properly understand the theory behind it.   

If you listened to my recording, i think you should notice that it sounds ''fuller'' with the 1 uf cap VS the 220 uf.  The difference is not extreme but still audible. The 220 uf cap seems to have cut some of the low-mid frequencies.

Maybe i will do another test with a 10 uf cap as this is what is used in the  Famicom RGB + Sound separation kit i bought.

Thank you for the recommendations 80sFREAK. When i get back to my Famicom for permanently modding it, i will possibly experiment with what you said.


P.S I also made a new series of recordings. This time I compared 4 different games on different machines.
Famicom, Sharp Twin, Famicom AV and US NES . Stay tuned, will make a thread about this later today  

[Julhan]

Help please!

I followed 80:s Freaks tutorial but I don't get any signal at all. I've both  tried the Q1- transistor and a 2N3906 pnp transistor. I know that the famicom did work before I started. Does anyone have a clue of what the problem(s) can be? It's a 1984 model by the way

[Julhan]

This one is with a 2N3906 transistor
Post Merge: November 13, 2012, 11:28:57 am
Hope you can make a diagnosis with this picture, were not able to attach more files. Forgot to mension, I used a 47 uF capacitor instead of a 33 uF

[2A03]

It's hard to tell but it looks like you're not getting 5V because of how you wired up the resistors. The 150 ohm resistor and the positive lead of the 47 uF cap are supposed to be tied together to the emitter, with the other end of the resistor going to a 5V source and the negative lead of the cap going to the 110 ohm resistor.

[Julhan]

Just checked with a multimeter,  the wiring are conductiv and  I get voltage. How do I check the transistor?

[famifan]

How do I check the transistor?

you'll do it with ease 
at first check both p-n junctions, just think of them as 2 diodes connected to B (E->B and C->B). Just  to be sure that DC current can run into that direction, not another.
then check current gain if you multimeter can do that

take as a rule to check every component right before the assemling

[Julhan]

The transistor seems to be fine as well..

[Julhan]

the voltage is 4.95

[Julhan]

exactly, I played smb 3  with the RF switch before starting the mod. Can the PAL-tv be a problem?

[keropi]

try playing with an lcd tv set thas is compatible with both pal and ntsc (99% are)