RF noise & homebrews?

[joeybastard]

I was playing the 2600 last night and I noticed that it seems like homebrew games are more prone to RF screen noise than original run Atari carts. At first I thought it might be my VCS so I played some thru my 7800. The 7800 was a little better in regards to screen noise but not much.

 

Am I imagining this or is it fact that the homebrews have more RF noise?

 

I know I can do the video mod and switch to RCA plugs but that's a different topic.

[+SpiceWare]

I noticed that with Seawolf, but not with any of the other homebrews I have.

[Thomas Jentzsch]

It best visible with bankswitched carts and a black background.

 

I wonder if it would be possible to add some simple shielding to the carts when making them.

[joeybastard]

So it is more evident in homebrews. I'm not imagining it. That's good to know.

[Lucky Man]

I've had a big interference problem with a few homebrew carts using my favorite 4-switch woody. It plays original games fine, but I get alot of noise on the screen with the homebrews.

 

I don't think they're putting any RF shielding in the new cart components. In fact, I sent a few back to Al and he built some new ones with different EPROM's that worked a little better.

 

After getting the worst interference yet with the last batch of games I ordered in December, I contacted Al who told me I needed to look into a possible connection problem in my system, especially since I am still using an Atari switchbox. So I tried it again using a direct coaxial connection and, surprisingly, I still got the interference. I then hooked up an Atari Jr. and got a crystal clear picture.

 

I'm not sure if this is a problem with my unit or an incompatibility with certain models, but I'm sending mine out for repair today to see if this problem can be fixed.

 

I do have a heavy-sixer packed away somewhere that I guess I should test, too, but that one never got a very good picture, so it might not be worth digging for.

[Dauber]

The only problem I've had is with lines/fuzz in the gray backgrounds in Toyshop Trouble....and even then, the game play is so addicting that I forget about it! (Also, the copy I have is a loaner that's just the PCB; wonder if maybe the lack of the plastic casing adds to it!)

[Lucky Man]

Yes, it's mostly lots of lines on the screen, especially in black backgrounds like Thomas said.

[Albert]

In my experience, the amount of RF noise generated by homebrew games can vary quite a bit. Very rarely have people ever come to me complaining about this issue. The homebrew games do not have an RF shield like regular mass produced Atari games. But this is also true of many third-party games. Some games produce more interference than others. Different boards and parts can produce varying amounts of noise. The system itself can affect how much noise there is. How the system is connected to the television probably affects this the most. The quality of a television's built-in TV tuner will also affect the amount of RF visible RF noise. Using an RF switchbox is probably guaranteed to net you some amount of visible RF interference. Using a coaxial adapter will greatly reduce this--I've very rarely had problems when doing so, and I've demoed a large number of homebrew games on various televisions over the years.

 

Of course, the best way to circumvent RF interference is to use a system that's been modified for composite and/or s-video output. Such as those produced by 8bitdomain.com:

 

http://www.8bitdomain.com/

 

..Al

[supercat]

The lack of shielding in homebrew carts will probably add somewhat to RF noise, as will the use of high-speed PLDs. These issues should be somewhat offset, however, by the fact that the carts contain bypass capacitors whereas many carts "back in the day" did not. I don't know of any really good cost-effective solution.

[Video]

I've noticed no RF noise on my 2600 games. Then again, I've never really been bothered by the old slider switchbox like everybody else apparently has.

 

 

 

It best visible with bankswitched carts and a black background.

 

I wonder if it would be possible to add some simple shielding to the carts when making them.

 

I don't know about mass production, it's probably easy to get a press to stamp metal plates to solder to the boards or something.

 

But an easy cheap way for a single problem game in your colection would be to take it appart, glue foil to the inside of the cart, and solder a wire from the foil to the ground pin.

[A.J. Franzman]

If the boards for the homebrews were designed to accept it, Al could easily install the shielding that comes in all the common carts he's taking apart for the shells he puts the new games in!

Edited March 7, 2007 by A.J. Franzman

[Thomas Jentzsch]

Of course, the best way to circumvent RF interference is to use a system that's been modified for composite and/or s-video output.

Actually my PAL jr. is modded for composite and I can still see the "RF noise".

[Albert]

Of course, the best way to circumvent RF interference is to use a system that's been modified for composite and/or s-video output.

Actually my PAL jr. is modded for composite and I can still see the "RF noise".

That seems odd to me--that would suggest the RF noise is being added to your composite video signal, as the television most certainly should not be picking it up. I have quite a few modified 2600 systems (using two different types of mods) and have never seen any RF noise from them, either on normal televisions or Commodore 1702 monitors. This also goes for 5200, 7800 and ColecoVision systems I have with similar composite / s-video mods. Sounds like either a bad television or a bad mod (I'd guess the latter).

 

..Al

[Thomas Jentzsch]

Mode? Mod?

[joeybastard]

 

 

Of course, the best way to circumvent RF interference is to use a system that's been modified for composite and/or s-video output. Such as those produced by 8bitdomain.com:

 

http://www.8bitdomain.com/

 

..Al

 

I'm using the coaxial adapter but some games still have it. It's not really that bad but I just noticed it's more than say Combat or Indy 500. I think I'm going to take the leap and look into the 8bitdomain mod.

 

Hmmm... Maybe I'll get the 7800 mod instead and kill two birds with one stone.

Edited March 7, 2007 by joeybastard

[Albert]

Mode? Mod?

Mod, sorry..

 

..Al

[A.J. Franzman]

If the "RF interference" you're seeing is a pattern of diagonal lines over the whole screen, it could be a power filtering problem. Try replacing the large electrolytic filter capacitor (2200 uF @ 16 volts or higher, axial leads), and if you have any small capacitors in clear glass packages (like diodes) beside the power jack or near the left side of the motherboard (on a Rev. C Junior here, they are C2, C21, C36 and C38), replace them with ceramic disc type 0.1 uF (may be marked "104").

 

On a 4-switch CX-2600A, the one beside the power jack will be C241 or C242.

Edited March 8, 2007 by A.J. Franzman

[LiQuiD iCe 9]

Actually my PAL jr. is modded for composite and I can still see the "RF noise". icon_confused.gif

 

you could go through a labor intensive solution like.

 

If the "RF interference" you're seeing is a pattern of diagonal lines over the whole screen, it could be a power filtering problem. Try replacing the large electrolytic filter capacitor (2200 uF @ 16 volts or higher, axial leads), and if you have any small capacitors in clear glass packages (like diodes) beside the power jack or near the left side of the motherboard (on a Rev. C Junior here, they are C2, C21, C36 and C38), replace them with ceramic disc type 0.1 uF (may be marked "104").

but first try different (new) composite wires and check the solder points on the mod a loose wire or weak connection can give a "noise" look too. also plug something else into your tv/vcr to check that. lastly make sure your wires are not laying on another electrical device as it could also make noise in your picture. and if none of that works rebuild your system and hope

[LiQuiD iCe 9]

Hmmm... Maybe I'll get the 7800 mod instead and kill two birds with one stone.

 

i have a new composite mod that gets rid of that graphic line that shows up on the right side of characters and objects like Harry in pitfall. My new mod looks to me to be more accurate in color and graphics (the way they line up) than many other mods. i haven't seen a real screen shot of the 8 bit mod yet only pics of a tv so maybe it is as good.

 

I'll try to post some screen shots tonight after LOST is over or an *.mpg so you can hear the sound. i was suprised to hear that combat, snoopy, pitfall II, and many more are in stereo or use 2 channel sound. i thought that they didn't program the games in stereo but that must be an urban legend because of 30 tested games only one (adventure) wasn't in stereo, all the sound came out one speaker.

[rheffera]

ive never noticed it with seawolf..in fact ive noticed more rf interference from old carts.

then i changed my 2600 jr which seemed to be a bit sensetive. the replcacment 2600 jr was much better. i think the other one had a loose rf connection or something..

[A.J. Franzman]

i was suprised to hear that combat, snoopy, pitfall II, and many more are in stereo or use 2 channel sound. i thought that they didn't program the games in stereo but that must be an urban legend because of 30 tested games only one (adventure) wasn't in stereo, all the sound came out one speaker.

Most games use both sound channels, if simply because it allows playing two different sounds at the same time, but only four (?) of the first nine (Combat, Air Sea Battle, Indy 500, Street Racer) and some homebrews were programmed so that the left/right position makes some sense. Sounds belonging to the left player come from the left channel, and right-player sounds from the right channel (regardless of screen position, so often in Combat and Indy the sound channels are "wrong" from a realism perspective.) But listening to games like Pitfall II, Missile Command and other later games, do the channel assignments make any sense to you in relation to the locations of objects on screen? AFAIK the only game programmed in true stereo is Skeleton+ (maybe the original Skeleton too); it plays the same sound at different volumes from both channels at the same time to create a panning effect, which the attentive player with a stereo console can use to help avoid defeat.

Edited March 14, 2007 by A.J. Franzman

[LiQuiD iCe 9]

Environmental stereo and a 2 channel or stereo effect are 2 different things. all real stereo is

Sounds belonging to the left player come from the left channel, and right-player sounds from the right channel (regardless of screen position, so often in Combat and Indy the sound channels are "wrong" from a realism perspective.)

just because it wasn't intelegent to what was happening on the screen doesn't redefine the stereo situation. if it was intelegent to the occuring changes to the screen and responded, it would be concidered a form of enviornmental stereo. the music in snoopy and pitfall II alternate left and right with different sounds that is stereo music or 2 channel sound just like your FM radio. some fx come out of the left and some out of the right. that is still stereo and more often than not the sounds don't play at the same time they alternate so they don't need to use 2 channels.

 

reguardless it put a new spin on the games and it fits the era because that is how most sound and music was played, basically inaccurate to the enviorment. no one was hooking up a 5.1 dolby to their atari for the reallistic feel of being there. if it wasn't intentional to program it that way why is it consistan that the left player is always the left speaker? it seems someone would've fudged it from one company to the next.

 

i'd suggest a switch to mono it out because some games like pheonix play music in one speaker and fx in the other. otherwise i think it sounds better in stereo and more "full" sounding like stereo should be.

 

I'll post my video some other time to many issues today.

[Thomas Jentzsch]

If the "RF interference" you're seeing is a pattern of diagonal lines over the whole screen...

No, I am seeing large, slightly grey rectangles over the black background.

[A.J. Franzman]

Environmental stereo and a 2 channel or stereo effect are 2 different things. all real stereo is

Sounds belonging to the left player come from the left channel, and right-player sounds from the right channel (regardless of screen position, so often in Combat and Indy the sound channels are "wrong" from a realism perspective.)

just because it wasn't intelegent to what was happening on the screen doesn't redefine the stereo situation. if it was intelegent to the occuring changes to the screen and responded, it would be concidered a form of enviornmental stereo. the music in snoopy and pitfall II alternate left and right with different sounds that is stereo music or 2 channel sound just like your FM radio. some fx come out of the left and some out of the right. that is still stereo and more often than not the sounds don't play at the same time they alternate so they don't need to use 2 channels.

Sorry, I disagree. Not all 2-channel sound is stereo sound. In stereo sound, the program content of the two channels must have some relationship to one another which enables a listener to spatially locate sound sources both at or near each speaker as well as between the speakers. I believe this is what you are redundantly calling "environmental stereo". On my FM radio, the DJs' voices and much of the music seems to come from between the speakers, often in the center. This is the definition of stereo.

 

 

reguardless it put a new spin on the games and it fits the era because that is how most sound and music was played, basically inaccurate to the enviorment. no one was hooking up a 5.1 dolby to their atari for the reallistic feel of being there. if it wasn't intentional to program it that way why is it consistan that the left player is always the left speaker? it seems someone would've fudged it from one company to the next.

 

i'd suggest a switch to mono it out because some games like pheonix play music in one speaker and fx in the other. otherwise i think it sounds better in stereo and more "full" sounding like stereo should be.

 

I'll post my video some other time to many issues today.

The left player is not "always the left speaker". Play Pitfall II. Play Space Invaders Game 33. Play Missile Command. After the first 9 games by Atari, no consideration was made by any of the programers regarding which channel to use for any particular sound (until hombrews came along), except to allow as much as possible for two sounds to play at the same time, because by then everyone knew that the 2-speakers-in-console design had been changed to mono audio through the TV by simply combining the two available voices into one channel.

[A.J. Franzman]

If the "RF interference" you're seeing is a pattern of diagonal lines over the whole screen...

No, I am seeing large, slightly grey rectangles over the black background.

Wow, that's a pattern I haven't seen before. Sorry, I'm out of ideas on this one!