Warning!!! 7800 power mod....

[+-^CrossBow^-]

Just a quick note to you guys on some findings I have had using the power modification to add an inline 1/8 inch phono jack to allow the use of the 2600 adapter over the 7800 one.

 

First as I think most of us know, the 7800 uses a 9 volt 1000ma (1amp) transformer for its power source. However, the 2600 uses a 9 volt 500ma (1/2amp) transformer. Most postings I have read in the past state that the 500ma difference on the 7800 doesn't matter to the 7800 and therefore should not cause any problems.

 

I am here to tell you what I have found doing this same modification myself. Basically I soldered two 4 inch lengths of 18 gauge wire to the negative and positive points marked on the 7800 board and also as dictated in the power mod webpages. I attached a 1/8 inch inline phono jack to allow me to use the 2600 power supply on the 7800.

 

What happens is this. The 7800 works great and nothing is amiss until after about 30 min or so of actual hard 7800 play. If you only play 2600 stuff this doesn't seem to happen. Either way, after I left BallBlazer running in demo mode (Thanks Kevin Ondre for the rare label variation!!!) I began to notice a Humming sound somewhere in the room. And I mean...a loud one at this. Looking around I found it to be the 2600 adapter itself that was humming! I turned off the 7800 where the humm then got much louder since the load was now removed from it and attempted to unplug the adapter from the strip to quiet it down. I lost at least one layer of flesh off my thumb, index and middle fingers of my right hand ripping that thing out. It was incredibly hot to the touch!!! I left it out unplugged all night and then tested again the next day. The adpater didn't humm anymore and never did while it was in the 2600 form which it came from or on the 7800 playing 2600 games. But as soon as I stuck a 7800 game in and started to play...well, within about 25-30 min that hum came back.

 

Moral is this...the 7800 side of the 7800 itself (Mainly the Maria graphics proc) does need a 1amp current to keep it going. And although a 2600 adapter will work with this mod...I wouldn't play any all nighters on the thing especially with a 7800 game actually plugged in!

 

I say do the modification so that you can purchase a universal adapter that meets the 9 volt 1 amp requirement. However, from what I have seen these typically run about 12-18 bucks locally. And 7800 adapters do not run much more on ebay.

 

Your choice friends but I do not recommend using a 2600 adapter on the 7800 for game play.

[+Mitch]

I've found that a Sega Genesis (original) power supply is the best to use when moding a 7800. The fact that the Genesis power supply is quite common is a big help.

 

Mitch

http://atari7800.atari.org

[+-^CrossBow^-]

Hmm...good idea...but here is the problem.

 

I have been to at least 3 different electronic stores in my town. And I am not talking Radio Shack here. They all have the female connector end for the PS itself...but all told me they would have to order the Male end for surface mount use. Problem with that is, none of them will order just one for me at only like a 1.50 each. So, instead I will hit a few thrifts or pawns and look for a cheap universal with at least an 800ma rating on it. I figure that should just about keep the 7800 happy and not melt the PS during those all night Food Fight and Xenophobe marathons I tend to play.

 

I will keep the Genesis plug in mind since I did notice that my 2600 PS is actually releasing 15.8 volts and not the 9 it specifies. I know that under a load it would be much different but still...doesn't 15.8 seem a tad on the high side?

 

Oh well, could be my old circa '77 2600 power supply was dying and connecting it to a 7800 just accelerated that process.

 

Interesting all these things.

 

Off topic...but does anybody know if there is a Stereo sound Mod for the 7800 like there is on the 2600 JR models?

 

That would be cool. Although both BallBlazer and Winter Games sound like crap on my stereo tv with the expanded sound turned on, figures.

[+Mitch]

It's funny you should mention Radio Shack but have you checked there? I think they may stock them.

 

Mitch

http://atari7800.atari.org

[Gunstar]

quote:

---

Originally posted by -^Cro§Bow^-:

 

Off topic...but does anybody know if there is a Stereo sound Mod for the 7800 like there is on the 2600 JR models?

 

That would be cool. Although both BallBlazer and Winter Games sound like crap on my stereo tv with the expanded sound turned on, figures.

---

 

I recently saw a picture of that audio/video mod for the 2600jr. too. However, it looked to me like there was only one (mono) rca output coming from the 2600jr board. Is that the way it is? It can hook up to a stereo, but only with one mono rca cord? Also, is this "expanded sound" your talking about an option on your tv? Or what?

 

But, yes there is a mod similiar to this for the 7800, here: 7800 mods

[Gunstar]

Sorry, I missed a letter in that link, here it is again:7800 mods

[cschell]

quote

I recently saw a picture of that audio/video mod for the 2600jr. too. However, it looked to me like there was only one (mono) rca output coming from the 2600jr board. Is that the way it is? It can hook up to a stereo, but only with one mono rca cord?  

 

Assuming you're talking about the picture of the 2600 I was using at CGE, the reason there is only one RCA connected is that it was connected to a mono monitor. You would use standard stereo RCA cables for stereo sound.

 

Chad

[DanBoris]

You findings are not surprising. The 7800 has all the chips from the 2600 in it plus a few chips more thus it would pull far more power then the 2600 AC adaptor could provide.

 

I am guessing the reason that it works in 2600 mode and not in 7800 mode is that the internal processor clock runs faster in 7800 mode then 2600 mode, and running a chip at a higher frequency generally causes it to draw more power.

 

Dan

[+rdemming]

quote

Off topic...but does anybody know if there is a Stereo sound Mod for the 7800 like there is on the 2600 JR models?  

 

Hi,

 

The 2600 soundchip (Inside Stella) has two channels but they are mixed inside the chip. So only a mono signal is leaving the chip. Thus it not possible to have 'real' stereo output.

 

The POKEY chip in the XL series (a double 2600 sound chip) has four channels but where also mixed inside the chip. The stereo upgrades for this machine worked by adding a second POKEY chip. This worked only with adapted software.

 

Regards,

 

Robert

[cschell]

quote:

---

The 2600 soundchip (Inside Stella) has two channels but they are mixed inside the chip. So only a mono signal is leaving the chip. Thus it not possible to have 'real' stereo output.

---

 

That's incorrect. They're mixed on the board, not on the chip. So you can get stereo sound just by picking the signals off the chip before they're mixed on the board.

 

Thus all the posts about how cool Threshold sounds in stereo. (I'm pretty sure it was Threshold.)

 

Chad

[Gunstar]

quote:

---

Originally posted by C. Schell:

Assuming you're talking about the picture of the 2600 I was using at CGE, the reason there is only one RCA connected is that it was connected to a mono monitor. You would use standard stereo RCA cables for stereo sound.

 

Chad

---

 

Yeah, that's what I was talking about, the picture I saw was not high enough res to see more than the one audio and one video cables coming out, I couldn't tell if it was stereo or not, so I assumed it was mono and that's Why I askedcommented. Thanks!

[Gunstar]

quote:

---

Originally posted by Robert:

The POKEY chip in the XL series (a double 2600 sound chip) has four channels but where also mixed inside the chip. The stereo upgrades for this machine worked by adding a second POKEY chip. This worked only with adapted software.

 

Regards,

 

Robert

---

 

Actually, the Pokey can have stereo sound from just the one chip, the reason they used two pokeys is so that they could get 16-bit stereo sound out of it, you see, the Pokey chip is capable of producing 16-bit sound, but only in mono, stereo with one chip would have been 8-bit. There were some odd-ball languages and music programs/players that used the full 16-bit potential of the Pokey, and some demos as well. Also the Pokey chip is MUCH more than just the 2600's chip "doubled" it is much, much, more advanced than that...

[+-^CrossBow^-]

Once Again I bow to the feet of Mitch!!!

 

You got it going on upstairs my friend. Why is it your the first person to mention using a Genny Model 1 PS adapter? Well..just like you said I took yet another trip to Radio Shack and sure enough they had the inline barrel jack male for the standard barrel adapter plugs. Need less to say in less than 5 minutes I took it back inside and hooked up my Genesis model 1 adapter to it and switched on the power. I think I must have let BallBlazer run in demo mode for like 3 hours while I worked on a Bio lab on the PC and then finally just turned it off.

 

Just speculation. But would a front loader NES adapter also work? They are 9 volts and 1.3 amps. A little bit more on the current perhaps...but I don't think it would cause a real problem for the 7800 at all.

 

BTW perhaps I am seeing things. But the 7800 appeared to actually run faster?!

 

Probably just getting late it was. Either way thank you ever so much for that suggestion as it is just as easy. And more importantly a much better fit spec wise to the real 7800 power supply.

[+rdemming]

quote:

---

That's incorrect. They're mixed on the board, not on the chip. So you can get stereo sound just by picking the signals off the chip before they're mixed on the board.

---

 

Oops, you are right. I've checked the schematics on http://www.atarihq.com/danb/a2600.html and the TIA chip does indeed have two audio outputs. I assumed that since the Pokey has one output, the TIA had one output aswell. Sorry.

 

 

quote

Actually, the Pokey can have stereo sound from just the one chip, the reason they used two pokeys is so that they could get 16-bit stereo sound out of it, you see, the Pokey chip is capable of producing 16-bit sound, but only in mono, stereo with one chip would have been 8-bit. There were some odd-ball languages and music programs/players that used the full 16-bit potential of the Pokey, and some demos as well. Also the Pokey chip is MUCH more than just the 2600's chip "doubled" it is much, much, more advanced than that...  

 

I've the schematics of the XL series and I see only one audio output on the POKEY. (See http://cat.asw.cz/~kubecj/achpokey.htm). Thus explain to me how you can get stereo sound with only one output.

 

The Pokey can indeed produce 16 bit sound but does this by combining two 8 bit channels into one 16 bit channel. Thus you can have four 8bit channels, two 8bit channels + one 16bit channel or two 16bit channels. Nothing to do with stereo though.

 

And yes, pokey has indeed some more posibilities than just a double TIA sound such as joining channels, high pass filter, 8bit frequency divider instead of 5bit.

 

Robert

[jsoper]

Yes, you can do stereo out of a 7800. In fact, if you provide a separate output for the external audio (ballblazer and others) you actually have 3-channel audio. Send 2 to a stereo and the third to the TV. NOTE: this can be done for intellivisions also.

 

I believe Turmoil is the game with the great stereo effects. Threshold may be good too.

John Soper

[+Mitch]

quote

Just speculation. But would a front loader NES adapter also work? They are 9 volts and 1.3 amps. A little bit more on the current perhaps...but I don't think it would cause a real problem for the 7800 at all.

 

I believe the NES adapters are AC not DC so it wouldn't work. You can however use the DC Genesis 1 adapter on a NES. I use my Genesis 1 adapter for all of the following systems (just not at the same time): Atari 2600 w/ adapter, 7800 w/ adapter, Lynx w/adapter, Jaguar, SMS, Genesis 1, NES, and SNES w/adapter. It's a mainstay on my powerstrip.

 

Mitch

http://atari7800.atari.org

[Gunstar]

quote:

---

Originally posted by Robert:

I've the schematics of the XL series and I see only one audio output on the POKEY. (See

http://cat.asw.cz/~kubecj/achpokey.htm)

. Thus explain to me how you can get stereo sound with only one output.

 

The Pokey can indeed produce 16 bit sound but does this by combining two 8 bit channels into one 16 bit channel. Thus you can have four 8bit channels, two 8bit channels + one 16bit channel or two 16bit channels. Nothing to do with stereo though.

 

And yes, pokey has indeed some more posibilities than just a double TIA sound such as joining channels, high pass filter, 8bit frequency divider instead of 5bit.

 

Robert

---

 

I figured (stereo sound)it could be done the the same way they modify the 2600 and 7800 to get stereo, I haven't looked at the pokey schematics for a long time, so you may be right about requireing two pokey chips, I just figured they used two, to get two 16-bit stereo channels instead of two 8-bit stereo channels. If indeed, The Pokey only has one output channel, then I guess you would need to Pokey's for stereo, I just thought I remembered seeing a mod way back when that could give 8-bit stereo with one pokey, I thought they even had some demo programs with it, but I could be mistaken...

[Albert]

quote:

---

Originally posted by Gunstar:

Yeah, that's what I was talking about, the picture I saw was not high enough res to see more than the one audio and one video cables coming out, I couldn't tell if it was stereo or not, so I assumed it was mono and that's Why I askedcommented. Thanks!

---

 

This picture should be of sufficient resolution, and if that's not enough I'll send you the original 2048x1536 image.

 

Chris Wilkson's 2600 Jr. S-Video Mod

 

..Al

 

[ 08-22-2001: Message edited by: Albert ]