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simon.plata

Simple DIY composite video mod

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Hi, I tried some simple composite video mods for my Atari 2600 with terrible results: Blurry image, ghosting, dark image, etc.

 

Then I designed my own mod and it works good enough for me. I wanted to share it with all who want to give a try.

 

First you need to remove some components from the board. I prefer to remove all unused components and store them.

 

post-62422-0-56111800-1509676365_thumb.png

 

But if you are more conservative then remove the following components only

 

post-62422-0-45672200-1509676412_thumb.png

 

Also, you need to remove or disconnect the "RF Modulator Module" and built the Video Amplifier.

 

I designed two simple video amplifiers:

 

The first is a simple one stage amplifier. This circuit Works good but due to the limited gain of only one amplification stage, there is some limitation in the brightness of the image. Most people will not notice it, but I wanted to ensure the best quality possible keeping it simple.

 

post-62422-0-47928700-1509676726_thumb.png

 

The second is a two stage amplifier. This is still a very simple circuit with flat gain up to 4.2MHz (Composite video band width) which ensures brightness and color preservation with minimun distortion. Use the 5K trimmer to adjust the gain (brigthness) of the signal. Teorically you will have 0dB or unity gain with 1577Ohm.

 

post-62422-0-87052200-1509677361.png

 

This is the Bode plot of my LTSpice simulation of the circuit

 

post-62422-0-41487100-1509677372_thumb.png

 

This is the board with the circuit installed

 

post-62422-0-36056400-1509677917_thumb.jpg

post-62422-0-42901800-1509678063_thumb.jpg

 

And finally this is the results:

 

Video on a CRT TV

post-62422-0-87139600-1509678189_thumb.jpg

 

Video on a LED TV

post-62422-0-03963700-1509678245_thumb.jpg

 

 

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This is my first time posting on this site I think, been lurking for many years though. Ive been trying to self mod my own 2600 and found your post. Ive used the AV mod found on instructables which is a quick mod but like you said is not the greatest. So I would like to try your version here and just a a question or two. First looking at your two stage design you have the cap marked as zero and I also don't see one on your board so Im assuming its no longer used but not sure if Im missing something. Also could you show where on the board that brown wire is connected? Thanks

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This is my first time posting on this site I think, been lurking for many years though. Ive been trying to self mod my own 2600 and found your post. Ive used the AV mod found on instructables which is a quick mod but like you said is not the greatest. So I would like to try your version here and just a a question or two. First looking at your two stage design you have the cap marked as zero and I also don't see one on your board so Im assuming its no longer used but not sure if Im missing something. Also could you show where on the board that brown wire is connected? Thanks

 

Hi, I'm glad you want to give it a try. I forget to indicate it is for NTSC signal bandwidth and may be not perform well on PAL.

 

The capacitor was tougth to increase the gain at high frequency and reduce the phase shift of the color signal. A 47pF capacitor gives a Little more crisp to the colors but it's not much noticiable, then I decided to not use it to keep the mod as simpleas possible.

 

The Brown wire is for the audio signal. This signal does not need additional amplification, then I just put a 100 Ohm resistor to ease the connection. The signal is taken from the node indicated by the red arrow. Attached some pictures for clarification.

 

post-62422-0-89522000-1510016641_thumb.png

 

post-62422-0-01406700-1510016815_thumb.jpg

 

post-62422-0-52190900-1510016929_thumb.jpg

 

Hope it Works good for your. Please share your results and don't hesitate to ask any other questions you have.

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I'll be doing this as well probably this weekend. Looks very nice.

 

Great!

One sugestion, I selected the resistor values to be easy to find in 1% metal film precisionn or in 5% carbón film. If you decide to use 5% tolerance components, just buy at least 5 of each and read the value with a multimeter and use the most close to the design value. Large deviation in the resistors values could affect the results because it is DC coupled.

 

Also try to test the transistors and use the ones with the higher gain.

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Why is Activision so hard to read? Camera issue?

 

Good question, I was asking to me the same thing.

 

I did some experiments and I found the resulting video is too Sharp. Even each pixel could be seen. This makes some text dificult to see, also camera is 50% guilty.

 

I added some distortion to the signal to make it more blurry and then it is easier to read. I take some pictures, first is the clean output:

 

post-62422-0-76834700-1510075664_thumb.jpg

 

This is with some added blur (distortion) and different camera settings:

 

post-62422-0-85710100-1510075820_thumb.jpg

 

post-62422-0-71703200-1510076105_thumb.jpg

 

If you prefer to add some distortion, just add a capacitor (from 47pF up to 100pF) between pin 4 (video signal from the Atari) and GND.

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Yah, Funvision. What are the round (+-) pairs in "design 1" ?

 

Do you mean V1 and V2?

 

They are voltaje sources to model the Atari's +5 volts power suply (V2) and the video signal (V1). But you don't need to worry about them, just ignore them because are just for simulation purposes in LTSpice.

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Hi.

 

I have tried this modification on my PAL 2600A ('Vader'). It is a little different from the UK models, but almost the same.

post-62455-0-38106700-1511261873_thumb.jpg

 

The components to remove are as here: https://www.thefuturewas8bit.com/index.php/2600_comp_mod

 

I lifted one end of the resistors and capacitor, then put some heat-shrink over the free end. It should be easy enough to replace the transistor and adjustable inductor if required, but keeping track of these three components would be more problematic so I left them in place.

post-62455-0-04979100-1511261954_thumb.jpg

 

Audio taken from the top of the board. Reinforced the wire with some heat shrink and routed it through the corner of the RF shield.

post-62455-0-62717500-1511261965_thumb.jpg

 

I made an error and put a 1K pot in when I intended a 2K, so I set that to maximum. I found the sound level to be quite high (too hot a signal), so put a 33K resistor in series after testing. The audio line is going to a pin at the edge for convenience -- it was directly attached, then I added the 33K resistor in series to mute the sound slightly.

post-62455-0-79735200-1511262142_thumb.jpg

 

post-62455-0-93712500-1511261978_thumb.jpg

 

The results are quite good, I think.

post-62455-0-46553500-1511262152_thumb.jpg

 

post-62455-0-16660400-1511262160_thumb.jpg

 

Thanks for sharing your design.

 

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Hi.

 

I have tried this modification on my PAL 2600A ('Vader'). It is a little different from the UK models, but almost the same.

attachicon.gifP1010897_c.jpg

 

The components to remove are as here: https://www.thefuturewas8bit.com/index.php/2600_comp_mod

 

I lifted one end of the resistors and capacitor, then put some heat-shrink over the free end. It should be easy enough to replace the transistor and adjustable inductor if required, but keeping track of these three components would be more problematic so I left them in place.

attachicon.gifP1010908_c.jpg

 

Audio taken from the top of the board. Reinforced the wire with some heat shrink and routed it through the corner of the RF shield.

attachicon.gifP1010909_c.jpg

 

I made an error and put a 1K pot in when I intended a 2K, so I set that to maximum. I found the sound level to be quite high (too hot a signal), so put a 33K resistor in series after testing. The audio line is going to a pin at the edge for convenience -- it was directly attached, then I added the 33K resistor in series to mute the sound slightly.

attachicon.gifP1010912_c.jpg

 

attachicon.gifP1010911_c.jpg

 

The results are quite good, I think.

attachicon.gifP1010916_c.jpg

 

attachicon.gifP1010917_c.jpg

 

Thanks for sharing your design.

 

Hi,

 

Nice work, I'm pleased it worked for you, moreover considering it was done on a PAL which requires a higher bandwidth.

 

Best regards,

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Hi, Here is a schematic and PCB design for the mod made in Eagle CAD. I will fabricate it to replace my generic PCB.

 

post-62422-0-00139200-1511299299_thumb.png

 

post-62422-0-75815900-1511299317.png

 

If someone want to fabricate your own PCB, just let me know. I can share the PDF or the Eagle files.

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Hi, Here is a schematic and PCB design for the mod made in Eagle CAD. I will fabricate it to replace my generic PCB.

 

attachicon.gifVideoAmp2S_SCH.png

 

attachicon.gifVideoAmp2S_BRD.png

 

If someone want to fabricate your own PCB, just let me know. I can share the PDF or the Eagle files.

Hi.

 

Thanks for these. That board looks just slightly neater than my two efforts ;) (The first of which decided it wouldnt work, so the one you see it my second improved attempt!) Shifting the breadboard circuit to protoboard was trickier that I had assumed, transistor pinouts being uncooperative.

 

Just a note that R5 and R6 may be best to have a couple of pads available. I used a 33R and 43R in parallel to get ~18R for R5, and two 150R in parallel to get 75R for R6.

 

This would require shifting the pads out and take a little more space, but would make it easier for people who dont have the exact resistors to hand.

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Hi.

 

Thanks for these. That board looks just slightly neater than my two efforts ;) (The first of which decided it wouldnt work, so the one you see it my second improved attempt!) Shifting the breadboard circuit to protoboard was trickier that I had assumed, transistor pinouts being uncooperative.

 

Just a note that R5 and R6 may be best to have a couple of pads available. I used a 33R and 43R in parallel to get ~18R for R5, and two 150R in parallel to get 75R for R6.

 

This would require shifting the pads out and take a little more space, but would make it easier for people who dont have the exact resistors to hand.

 

Yeah, good advice! I will take it into account for the next revisión. I didn't know these resistor values were not easy to find everywhere, I selected these values because they are into the estandar 5% values.

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Yeah, good advice! I will take it into account for the next revisión. I didn't know these resistor values were not easy to find everywhere, I selected these values because they are into the estandar 5% values.

It isn’t unusual to only have the E6 values available. 75R is only in the E24 and E48 series, and not that common in my experience. 18R is in the E12 series, but often not included in bulk lots as I had on hand where they use the E6 series as the basis for selection of values.

 

The tolerance doesn’t seem to have much to do with the series used, now. The metal film ones I have are supposedly 1%, and actually closer to 2% —although perhaps they got some black paint in their red. ;)

 

(Chinese sourced stuff is fine for general messing around, but probably not a good idea if you want precision.)

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Going into a woody 4-switch tomorrow. Thanks for this. I will post results as compared to the single transistor mod that's currently installed.

 

post-10491-0-33044900-1516070657.jpg

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Well, I got this installed. I have to tell you this is the best picture I have seen on a 2600. Great job with this!

 

The previous single transistor, 2 resistor composite mod I was using had a terrible picture. It was dark and had static patterns. It looked bad on my big flat screen and barely passable on a CRT.

 

This two-transistor circuit is like night and day..It looks very clear without any static or noise and is plenty bright with nicely saturated colors. It was easy to build too thanks to the schematic and board layout as well as the above pictures. Thanks again.

 

Norm

Edited by norm8332
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Well, I got this installed. I have to tell you this is the best picture I have seen on a 2600. Great job with this!

 

The previous single transistor, 2 resistor composite mod I was using had a terrible picture. It was dark and had static patterns. It looked bad on my big flat screen and barely passable on a CRT.

 

This two-transistor circuit is like night and day..It looks very clear without any static or noise and is plenty bright with nicely saturated colors. It was easy to build too thanks to the schematic and board layout as well as the above pictures. Thanks again.

 

Norm

 

Hi norm, I'm very glad it worked for you!

 

Thank you very much for your kind comments. I'm happy making a little contribution for the 2600 community!

 

Best regards,

 

Simon

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I'm gonna go for it too, but I have to collect some parts first. Looks promising!

 

Darryl

 

Hi Darryl,

 

Good to hear you will give it a try. Please let us know if it works for you.

 

Regards,

 

Simon

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This looks fantastic.

 

I have been using an A/V mod that I purchase off eBay https://www.ebay.com/itm/Atari-2600-7800-A-V-Composite-RCA-Audio-Video-Mod-Kit-NEW-IMPROVED-KIT-1G-/311705759237?_trksid=p5731.m3795

 

I have been pleased with it so far, but I am always looking for something potentially better. I am planning to install your design in a light 6'er as soon as I can get all the components together.

 

If possible I would like to get a copy of your PDF Eagle file.

 

Thanks.

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This looks fantastic.

 

I have been using an A/V mod that I purchase off eBay https://www.ebay.com/itm/Atari-2600-7800-A-V-Composite-RCA-Audio-Video-Mod-Kit-NEW-IMPROVED-KIT-1G-/311705759237?_trksid=p5731.m3795

 

I have been pleased with it so far, but I am always looking for something potentially better. I am planning to install your design in a light 6'er as soon as I can get all the components together.

 

If possible I would like to get a copy of your PDF Eagle file.

 

Thanks.

 

Hi,

 

Please see the PDF files attached. Sorry for the delay.

 

VideoAmp2S_MSK.pdf

VideoAmp2S_SLK.pdf

 

Best regards,

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