Adjusting Volume on 7800

[7800 Emucoder]

http://www.vintagega...ion-guide-7800/

 

This one.

 

desiv

 

That's basically the same exact mod as the "Easier 7800 composite Mod" thread one.

[desiv]

That's basically the same exact mod as the "Easier 7800 composite Mod" thread one.

Thanx..

That's a long thread, but I found this in in so far:

6. I connected a resistor to the bottom of C14. This is the audio out. Any resistor value between 47K and 68K should be fine. The other end of the resistor goes to the RCA connector Now clip the top connection (towards the back of the unit/cart cup) of R5 and R6, but leave the bottom connected to the motherboard. Solder the two clipped end together, and then attach a 1uf capacitor between the two soldered together ends and the center pole of the audio RCA jack. This will give you both standard TIA audio and Pokey audio for games that have that.

7. Run a wire from the top of C10 to the audio jack. This is the POKEY audio. I actually made the connection by running a wire from C10 to where the audio jack connects to the resistor I added for the audio output.

 

So. it looks like our MOD used step 7, which is now deprecated.

Not sure if step 6, with it's changes (and the other steps), is significantly different than our mod yet..

Will have to dig in when I get a chance...

 

I can see why it didn't really get noticed tho.

I tried BallBlazer again last night (what I usually use to test Pokey audio) and it's not that noticeable.

 

I'm guessing the game "sounds" would be much louder than the music normally, but it doesn't sound too bad with this flawed fix.

It isn't until you load some other Pokey games (Commando) that you REALLY notice it..

 

I'm wondering if a trim pot of some value (20k?) across the TIA audio feed to the RCA jack might be a simpler workaround than repairing the "mod" at this stage...

 

Hmmm..

 

Thanx,

 

desiv

Edited January 23, 2013 by desiv

[+Mitch]

Wow, that audio mod is way over complicated. You are better off using the audio method 2 from this AV mod: http://atari7800.org/7800mod/7800_mod.htm

 

Mitch

[7800 Emucoder]

Wow, that audio mod is way over complicated. You are better off using the audio method 2 from this AV mod: http://atari7800.org...od/7800_mod.htm

 

Mitch

 

the one I explained is even simpler than that. Instead of soldering two new resistors at 6.8k and 18k to those points, just clip the already existing 6.8k and 18k resistors right there on the motherboard at their top posts (towards the back of the console) and solder them together three. You don't even really need the 1uf cap. the resistors are already there on the board. just use those.

Edited January 23, 2013 by 7800 Emucoder

[desiv]

Well, in the "still hoping I don't have to reverse too much of what I've don to fix this" vein, I picked up a couple of trim pots today to test.

Unfortunately, I stopped by my local Radio Shack (it was lunch and I didn't have time to hit the real electronic shop) and they didn't have any 20k ones.

So I grabbed a 10k and a 100k.

 

I'll try to get to it this weekend.

If it works and decreases the TIA volume enough, I should be able to read the resistance its set at on the trim pot so that just a resistor at that value will work.

 

desiv

Edited January 24, 2013 by desiv

[desiv]

OK, looking good now..

Interesting, when I disconnected the TIA, POKEY audio automatically got louder..

 

Anyway, with the trim pot (the 10K one), it is making a difference. I have it at 7.80K OHMS (If I'm reading my multimeter correctly).

(I see they sell 7.5k which would probably be close enough.)

 

Now, I don't know what wattage you would need for a resistor tho..

 

Anyone who understands electronics have an idea on that?

I might just stick with the trim pot I have. If it lasts (if I'm not putting too many WATTs thru it), it's nice that I could tweak it a bit later if needed. And I think it will install fine in the case... I'm going to solder it together in a bit.

Thanx,

 

Desi

(p.s. I have no idea what is "should" sound like. I just know this value seems good to me; tested with Commando and Beef Drop so far. )

Edited January 25, 2013 by desiv

[desiv]

Soldering took too long and I can't edit..

 

Anyway, I think I like the volume mix where it is..

Commando intro is still pretty loud, but in game it's much better..

BallBlazer is still good.

Beef Drop, PacMan/MsPacman I think are about right...

I just listened to some youtube vids for Commando, and they have the music (Pokey) and games sounds (TIA) about the same, and my mod/fix has the music a bit quieter than the game sounds still. But I still think I like that better.

 

I was going to take a pic, but my wife has the nice camera and I'm left with my phone, which has a really bad camera.

Also, it's just a pic of a trim pot soldered to the side of an RCA jack with a wire coming off the side of it.

It just wasn't working with my phone tho, so just imagine it..

And while you are imagining it, imaging the solder joints MUCH nicer than the ones I did...

 

desiv

p.s. I actually had to replace the wire also, because when I clipped it (I was going to put the trim pot in about the middle of the wire), it snapped where I had attached it to the RCA jack. Guess I bent that wire back and forth too much when I was mounting it. So in the pic, imagine a white wire, as I didn't have any red handy.

Also, the trim pot cost about $2, so not too bad. Of course, a single resistor would be less.

Edited January 25, 2013 by desiv

[Dauber]

Hey, sorry to resurrect this dead thread, but...I FINALLY got some 20k pots for my mod...I say "some" because you know how hard it is to buy just ONE? Gotta buy 'em in 5-packs. :/

 

Anyhoo...how exactly do I solder one of these in? There are three pins....how to they get wired in?? (I PM'ed the OP but he's been inactive for quite a while and hasn't responded...)

[SIO2]

the one I explained is even simpler than that. Instead of soldering two new resistors at 6.8k and 18k to those points, just clip the already existing 6.8k and 18k resistors right there on the motherboard at their top posts (towards the back of the console) and solder them together three. You don't even really need the 1uf cap. the resistors are already there on the board. just use those.

As a person with no formal electronics training, I was puzzled about the 1uf capacitor in the audio line. This video helped me understand what the capacitor is doing. I thought I would share the link: www.youtube.com/watch?v=eF8e-FmtDh4

[DEANJIMMY]

I've got a french PAL 7800 with scart cable with the same Problem.

 

The Pokey music of commando plays at very low volume while the sound effects from the TIA are quite loud.

 

Basically this console is an official sold AV mod. I wonder if somebody knows if a trim pot can be added and where.

 

It does not have an HF modulator at all but an installed daughter board at the same place wirh 2 pots for the Video Signal only.

[+Mitch]

I've got a french PAL 7800 with scart cable with the same Problem.

 

The Pokey music of commando plays at very low volume while the sound effects from the TIA are quite loud.

 

Basically this console is an official sold AV mod. I wonder if somebody knows if a trim pot can be added and where.

 

It does not have an HF modulator at all but an installed daughter board at the same place wirh 2 pots for the Video Signal only.

 

This is a known issue. Atari screwed up one of the resistor values for the audio circuit on the PAL 7800s. You have to replace one resistor and the issue will be fixed. I don't have the schematics in front of me so I can't tell you which one at the moment.

 

Mitch

[DEANJIMMY]

Many thanks for the info from Mitch!

 

Does anyone have a Picture where this resistor is placed on a French PAL board and the value to replace with?

 

The soldering would not be a Problem

[+Mitch]

You need to replace the resistor at R5 on the PAL schematic. The incorrect value is 6.8K, it should be 18K.

On the later PAL 7800 motherboard which I believe the SCART 7800 uses, the resistor location may be different. I would need to open up my SCART 7800 to verify though.

 

Mitch

[Rhomaios]

What about on NTSC? I have the same problem on my NTSC ES-modded 7800.

[DEANJIMMY]

Many thanks for the info about the correct value of R5!

 

I opened my French PAL Scart 7800 yesterday but unfortunaly did not took a photo when I removed the shielding.

I did not search for R5, as I read this post afterwards but tried to adjust Colors for 7800 and 2600 games.

2600 adjustment works fine, but is not possible to get rid of yellow/green faces in commando but most games are OK

 

Well, this RGB hack from Atari is quite interesting. There is a daughter board for the SECAM stuff which covers the pot for 2600 Color.

If you don't know where it is placed you never will find that pot!

Then there is a daughter board for the RGB connector. Many wires, 3 Pots for RGB Video, many added resistors... it also covers other components.

The Boards look OK but the soldering of wires, resistors, pots is quite a mess. The Person who did this, probalby touched a soldering iron for the very first time (Tramiel Quality?! )

I can imagine now why most of the posted mods have a better Video Quality then this official Version from Atari... anyway I am quite happy with this unique 7800

 

From Pictures of an NTSC or "normal" PAL board it would be hard to find R5.

When I open it next time I will have a look but as the hack is of such a bad Quality I do not want to touch/open it too often