Atari 2600 audio mod. Help needed.

[Atariuser]

Hello everyone. This is my first post so please be gentle.

 

Apologies in advance if this has already been touched on.

 

I just modded my 2600 four switch to display composite video and audio for each channel. I have some minor problems however.

 

The video is 100% fantastic. I now cannot live without it.

 

The audio is stable but there is very loud low-end humming and very high pitched noise. The audio is a pretty low volume as well and when turned up it just makes the noise louder as well.

 

I noticed that when the top of the 2600 is off the high pitched noise isn't as loud, it is only when I put the top on.

Also, when I put my finger on the ground of the 2600 the humming stops. It should be noted that the humming is still present when I have the power disconnected.

 

I have each of the 1/4 jacks connected to it's own resistor which goes straight to the corresponding audio pin on the chip.

 

Here are my questions:

 

How can I boost the audio signal without boosting the noise? I'd like to hit the problem at it's source instead of raising the volume on the mixer.

I'm assuming the high end noise is rf? I tried using a ferrite ring but no luck. Any suggestions?

I'm also assuming that the low hum is a ground loop of sorts....but no power is connected. How can I trick my atari into thinking my finger is still on the ground?

 

hahaha

 

Somewhat of a lamer when it comes to circuits so please help out a fellow atari user.

 

btw...Midwest Gaming Classic was very fun this year! Thanks for the memories and the good time!

[A.J. Franzman]

Not enough information!

 

What are the resistors for, and how are they connected? Do you have a capacitor in line with each jack? Did you connect the outer part of each jack to the 2600's circuit ground? Is this mod something you found online somewhere (link, please), or your own invention? If it's your own, can you provide a circuit diagram or a good photo(s) of what you did?

Edited June 12, 2007 by A.J. Franzman

[Atariuser]

Not enough information!

 

What are the resistors for, and how are they connected? Do you have a capacitor in line with each jack? Did you connect the outer part of each jack to the 2600's circuit ground? Is this mod something you found online somewhere (link, please), or your own invention? If it's your own, can you provide a circuit diagram or a good photo(s) of what you did?

 

 

What are the resistors for, and how are they connected?

 

I just did what it said so I'm not sure what they are for. I soldered the resistors to the pins as mentioned and connected a wire from that to a 1/4 socket each.

 

Do you have a capacitor in line with each jack?

 

No. I'm not completely sure what those do. I tried but how would I connect that correctly? What do they look like?

 

Did you connect the outer part of each jack to the 2600's circuit ground?

 

Yes.

 

 

Here is where I found the mod:

 

http://www94.pair.com/jsoper/2600_stereo.html

 

 

I have no idea what a "resistor pullup" is and how to find 5v to connect it to.

 

Also I didn't add the .1uf caps it said because I couldn't hear the audio any longer....unless I used the wrong cap? It was big and blue and that is all I know.

 

ahahaha

 

This is kinda what my situation looks like:

 

 

 

-/\/\/-- = 1.8K

 

 

TIA12<---------------- --/\/\/-- ------------|(-------------->Audio R?

 

 

 

 

 

 

TIA13<----------------- --/\/\/-- -----------|(-------------->Audio L?

 

 

I hope this helps.

Edited June 12, 2007 by Atariuser

[Quadhorn]

This is kinda what my situation looks like:

 

 

 

-/\/\/-- = 1.8K

 

 

TIA12<---------------- --/\/\/-- ------------|(-------------->Audio R?

 

 

 

 

 

 

TIA13<----------------- --/\/\/-- -----------|(-------------->Audio L?

 

 

I hope this helps.

 

Umm, that might be the problem. The 1k8 resistors should _not_ be in series. These are the "pull-up resistors". They should connect between the p12 and p13 TIA pins (the ones you have marked TIA12 and TIA13) and a +5V supply, such as the +5V / Vcc / pin 20 of the TIA. Have a look at the following for the TIA pinout:

 

http://www.atarihq.com/danb/tia.shtml

 

Also I didn't add the .1uf caps it said because I couldn't hear the audio any longer....unless I used the wrong cap? It was big and blue and that is all I know.

 

In fairness, the page does say "0.1microF to 10microF". The problem with that is that the resistor and capacitor pairs form a high pass filter; using the 0.1microF capacitors cuts off signals below about 350Hz, cutting into what you can hear. Those capacitors really need to be of a greater value. Try to find at least 1microF, larger if you can.

 

Assuming that the diagram is correct (can't think why not off-hand), if you use a polar capacitor (marked with either a positive or a negative side, depending on type) make sure that the positive side is connected to the TIA and the negative side is connected to the output socket. Otherwise they might catch on fire. Aluminium electrolytics will have the negative terminal marked. Tantalum electrolytics will have the positive terminal marked.

 

What you need is:

 

 

TIA12-------|(----AudioR

|

<

<

<

|

TIA20

|

<

<

<

|

TIA13-------|(----AudioL

 

Where the sets of "<"'s are the two resistors and the "|("'s are the capacitors.

 

'Make any sense? Any more trouble, give us a shout and maybe a photo of the setup, if possible.

[A.J. Franzman]

Do you have a capacitor in line with each jack?

No. I'm not completely sure what those do. I tried but how would I connect that correctly? What do they look like?

<snip>

 

This is kinda what my situation looks like:

 

 

-/\/\/-- = 1.8K

 

 

TIA12<---------------- --/\/\/-- ------------|(-------------->Audio R?

 

 

 

TIA13<----------------- --/\/\/-- -----------|(-------------->Audio L?

 

 

I hope this helps.

If you don't know what a capacitor looks like, then what do you think the symbol "---|(---" represents in your diagram above? (What did you connect in the circuit at those locations?)

[A.J. Franzman]

In fairness, the page does say "0.1microF to 10microF". The problem with that is that the resistor and capacitor pairs form a high pass filter; using the 0.1microF capacitors cuts off signals below about 350Hz, cutting into what you can hear. Those capacitors really need to be of a greater value. Try to find at least 1microF, larger if you can.

The 2600 was originally made with a 0.1 uF blocking capacitor in the audio line; that's what it's designed for. The high-pass filtering is useful to block things like 60 Hz and 120 Hz AC hum , and other undesired pops, thumps and low frequency junk that may be generated from the switches, controllers, etc. I have a strong suspicion that Atariuser did not put capacitors where his diagram shows them, or he put in "big blue" ones of much higher value than they should be.

[Atariuser]

I have a strong suspicion that Atariuser did not put capacitors where his diagram shows them, or he put in "big blue" ones of much higher value than they should be.

 

Of course I didn't. I have no idea what I'm doing which is why I asked!

[SINGLE TOOTH]

Is there a reason you want the "stereo" sound? I dont really see how useful that is unless your making music on the atari or something like that.

 

Otherwise, there are other sound mods that work fine, and are super simple.

 

This site will show you how.

[Atariuser]

Quadhorn:

 

 

You my friend are a champion. All it took was that little diagram and I've learned much more than I thought I would.

 

It sounds crystal clear and I swear that aside from the clarity it sounds much, much, fuller.

 

Thank you for taking the time out to help me. I'm sure that this wont be the last time I need it.

 

[Quadhorn]

Fantastic, Atariuser. It's good to know I've not gone insane quite yet.

 

The 2600 was originally made with a 0.1 uF blocking capacitor in the audio line; that's what it's designed for. The high-pass filtering is useful to block things like 60 Hz and 120 Hz AC hum , {etc.}

 

Btw, AJF's got a point. Aside from removing the DC so that it doesn't fry your speakers, the HP filter also removes low frequency hum (50/100 Hz or 60/120 Hz). If it works fine, great, leave it as it is. If you have problems with low frequency noise you might have to tweak the capacitor value to get a balance between audio range and noise suppression.

 

Happy gaming, man.

[mimo]

Is there a reason you want the "stereo" sound? I dont really see how useful that is unless your making music on the atari or something like that.

 

Otherwise, there are other sound mods that work fine, and are super simple.

 

This site will show you how.

Does this work for the six switch as well?

[Atariuser]

I used a 10uf cap and I cannot believe how pristine the audio is. I'm assuming the hum / whine was from my interesting mod job. hahahaha

 

Both are gone now.

[SINGLE TOOTH]

Is there a reason you want the "stereo" sound? I dont really see how useful that is unless your making music on the atari or something like that.

 

Otherwise, there are other sound mods that work fine, and are super simple.

 

This site will show you how.

Does this work for the six switch as well?

 

No. That was for the 4-switch.

 

Check out This Site and there will be a 6-switch mod on that page.