Returning ex-7800 owner with my "new" 7800.

[Gunstar]

1 minute ago, juansolo said:

The Dragonfly isn't stereo. There's only a single audio line that comes from the cart slot. The dual Pokey support just gives you 8 channel sound or, IIRC, less channels at higher quality. Not 100% on that though. The Covox support comes with the Pokeymax also. If you just fit a standard Pokey, you just get standard Pokey support. Currently the dual pokey and covox isn't supported by much other than demos. The YM is used by the Pac-Man 40th Anniversary collection and quite a few titles use the single pokey.

 

The PAL 7800 has a single audio feed from the TIA also, that and the cart audio are mixed together to a single mono output. The NTSC 7800 has two audio channels from the TIA and the single cart audio. It's not technically stereo though. You can wire it as stereo but it won't be right and to make it pseudo stereo would require some active mixing to make it not sound odd. They're again, just all blended together as a single mono out.

Thanks, I'm quite aware, after pouring over PAL 7800 schematics and audio/video mods the last 24 hours of how the audio and video all works. I just didn't know how the Dragonfly worked with a Pokeymax installed, or YM, Crossbow cleared that up for me. I'll be modding the Dragonfly with a stereo out-jack and line-level audio pre-amp just like I did with the Dual Pokey and Pokeymax upgrades I've already installed in Atari 8-bits. But the Pokeymax for the DragonFly is down the road a bit, I'll just be using a standard Pokey for now, I'm not interested in trying to pull off some pseudo stereo from the TIA's two audio channels. I remember a mod I did to a 1040STE back in the day with it's 3 channel audio off it's audio chip for pseudo stereo. It worked pretty good actually, until you tried listening to digitized stuff that used all 3 audio channels for definition and how broken it sounded with the "stereo" upgrade. LOL.

 

I place my pre-order for the Dragonfly with just the YM board, because @DrVenkman already made me aware of it's use and that there is nothing for the Pokeymax yet, so I didn't get it with the DF and will use one of my extra Pokey chips left over from Pokeymax upgrades already done.

 

I appreciate your warnings, even though they are a bit too late.

[+-^CrossBow^-]

Technically the DF is stereo. There are three trimmers on the back of the DF PCB to adjust the volume levels. One each for dual pokey and the third for adjusting the YM volume. RJ actually posted video and a picture showing where he tapped the audio directly from the DF to achieve the dual pokey stereo effect. Basically just tap the audio from the resistors after the trimmers is all that is needed. 

 

So yes, with an external audio output jack from the DF itself, you could get separate left and right audio from each pokey that the MAX is generating. The YM only has the single audio channel however, and while I've not looked up the pinouts on the 2151, it might only have a single audio out pin on it I'm guessing?

 

[Gunstar]

I only have experience with the YM2149/YM2149F in the ST series. I haven't bothered to look at a data sheet on the YM2151 yet, so I don't know how different they are. But if the YM2151 has multiple channels, it may have  multiple audio pins out like the 2149's 3 audio out pins, But the Dragonfly might use it just like the ST did with the 2149, out one mono channel. If that is true, then the channels could be separated as well.

 

I did a stereo mod years ago (my ST's and tons of other stuff were stolen out of a rental storage locker/garage) for three channel stereo on my 1040ST, as it had a separate out for all 3 sound channels and it was just wires from those pins to a small pre-amp board I made with resisters and pots and capacitors to 3 RCA jacks out the back of the ST. So you had left, right and center channels.

 

It worked great for most games, as long as there wasn't digitized stuff, then it got wonky since the digitizers used all three channels for maximum bits/frequency/octaves, Sort of like how the Pokey/pokeymax can combine two of it's 8-bit voices/channels into 16-bit. But the digitizers & digital audio files expected to be coming out of a mono channel and when the digitized audio was separated out three channels...wow! Of course, just like the 800 and 7800, you still had the stock mono audio out through the monitor jack, so you would keep that hooked up too, and shut off whatever you had the stereo mod output too when needed.

Edited July 27, 2021 by Gunstar

[Gunstar]

So, as I said previously, I've been pouring over mod schematics and PAL 7800 schematics over the last 24 hours. I actually became so engrossed in studying the 7800 schematics that it was 3:30 AM before I realized I'd better get to bed. I got 3 hours of sleep and worked all day to day. But I'm still awake and typing away here now...

 

Anyway, My first thought was to go grab the Atari 7800 Field Service Manual from Atarimania archives to find that the 7800 section is totally empty still at this time. So I started searching elsewhere to read that Atari never made a FSM for the 7800?!? But luckily I found the PDF's and Jpeg's of tons of info (around 50 pages IIRC?) that Kurt Vendel found while dumpster diving at Atari back in the day! So I found the 4 image J-peg of the PAL 7800 schematic, printed it out landscape style at best quality on 4 sheets of paper, stretching with no borders, and then tape all four together. There is some over-lap, so I had to match them and tape them together. But I now have a large schematic that I studied for about 6 hours last night, while also pouring over all the available video mods I could find that were done on the 7800.

 

Sorry, I had to cover some parts of the schematic because I've already jotted down some top secret stuff on those areas...I'll reveal all if my video circuit plan is a success.

Edited July 27, 2021 by Gunstar

[juansolo]

I have an alternate schematic to that one also that might be useful (it's easier to read). Plus I extracted the video section from it to make that easier to read when we did the video mod.

[rj1307]

On 7/27/2021 at 11:43 PM, -^CrossBow^- said:

Technically the DF is stereo. There are three trimmers on the back of the DF PCB to adjust the volume levels. One each for dual pokey and the third for adjusting the YM volume. RJ actually posted video and a picture showing where he tapped the audio directly from the DF to achieve the dual pokey stereo effect. Basically just tap the audio from the resistors after the trimmers is all that is needed. 

 

So yes, with an external audio output jack from the DF itself, you could get separate left and right audio from each pokey that the MAX is generating. The YM only has the single audio channel however, and while I've not looked up the pinouts on the 2151, it might only have a single audio out pin on it I'm guessing?

 

This time you are wrong  

 

 

[+-^CrossBow^-]

1 hour ago, rj1307 said:

This time you are wrong  

 

 

Very cool and I figured it had more than one channel I just hadn't looked at the pinouts to verify that. But you have them combined together at the volume trimmer though right?

 

[rj1307]

Yes, these two 4k7 resistors sum both channels into one that is adjustable. 

 

 

[+-^CrossBow^-]

6 hours ago, rj1307 said:

Yes, these two 4k7 resistors sum both channels into one that is adjustable. 

 

 

So again in theory if you wanted 2 channel output from the 2151, you just tap the audio right before those resistors and out to a separate jack. Out of curiosity, why didn't wire up the YM with two trimmers as you did for the pokey? Or more exact, why did you sum up the two channels into a single output channel then? I know the audio out for the 7800 is a single line but again just curious?

 

 

[juansolo]

After the resistors unless you want to adjust the balance of them with other signals you're mixing them with in which case you might want to use different value resistors. You'd want to lift them regardless to stop them combining together. Same as lifting the resistors on the 7800 and connecting to the ends of those.

Edited August 2, 2021 by juansolo

[rj1307]

19 hours ago, -^CrossBow^- said:

Out of curiosity, why didn't wire up the YM with two trimmers as you did for the pokey? Or more exact, why did you sum up the two channels into a single output channel then? I know the audio out for the 7800 is a single line but again just curious?

 

 

Because the YM2151 was supposed to work with the mono YM3014 converter, I designed the DF for it. But in the end the YM3012 stereo DAC turned out to be more accessible, so I only changed the YM module.

As you wrote, take the signals for the additional stereo output exactly from the points I marked. 

[sn8k]

Love my 7800 but I never liked how some carts slide right in no issues..... and then other normal Atari carts barely go in and its a pain in the ass to both insert and remove them. Then there's all the other oddly shaped carts like imagic and intellivision carts... always have that issue.

 

And it's  not like this only happens to 2600 games..... I have 7800 games that slide right in and others that I have to ram in and yank out. Kind of a pain in the ass......and totally worth it.

[sn8k]

Think Im gonna do some Missing In Action tonight...... wish it was Toki. But that's a story for another day. 

[+SmittyB]

1 hour ago, sn8k said:

Then there's all the other oddly shaped carts like imagic and intellivision carts

Sounds like you could use one of these https://winzmods.com/product/atari-2600-lock-on-cartridge/

It won't help with the 7800 carts you're having problems with as it's 2600 only, but it gets around the problem of oversized third party 2600 cartridges.