Colecovision Composite mod

[nathanallan]

> Just a note to anyone wanting to add the composite video output to a

> colecovision. One of the better approaches to this is the op amp based

> buffer (as opposed to the single transistor circuit, which isn't so

> hot). You need a high speed wide bandwidth part to work properly, and

> the popular part on modders webpages is the obsolete LM318. These are

> not as available as they once were and I didn't have any in my parts

> stock, so I tried a CA3140. It worked, but the bandwidth wasn't good

> enough to render all colors correctly and also caused some slight

> tearing on the edges of the pix. Since it was used as a voltage

> follower, I remembered I had ample stock on the LM318, which is a

> dedicated voltage follower chip and pin compatible with the single op

> amp pinout. Its also rated for 20Mhz, so this is more than enough for

> composite video. Shoved it in and it took right off and looked great.

> It also reduces the parts count for the circuit (parts in feedback

> loop can be omitted), simplifying the mod and taking up less real

> estate. And.....its a common part still in production.

 

Not sure if I posted this yet, but there you guys go, thought you all would like to see it.

[boardjunkie]

> Just a note to anyone wanting to add the composite video output to a

> colecovision. One of the better approaches to this is the op amp based

> buffer (as opposed to the single transistor circuit, which isn't so

> hot). You need a high speed wide bandwidth part to work properly, and

> the popular part on modders webpages is the obsolete LM318. These are

> not as available as they once were and I didn't have any in my parts

> stock, so I tried a CA3140. It worked, but the bandwidth wasn't good

> enough to render all colors correctly and also caused some slight

> tearing on the edges of the pix. Since it was used as a voltage

> follower, I remembered I had ample stock on the LM318, which is a

> dedicated voltage follower chip and pin compatible with the single op

> amp pinout. Its also rated for 20Mhz, so this is more than enough for

> composite video. Shoved it in and it took right off and looked great.

> It also reduces the parts count for the circuit (parts in feedback

> loop can be omitted), simplifying the mod and taking up less real

> estate. And.....its a common part still in production.

 

Not sure if I posted this yet, but there you guys go, thought you all would like to see it.

 

I posted it already.

 

**NOTE** - There is a typo in that text. The improved part is an LM310, not 318.

[nathanallan]

Doh! I just wanted to make sure it got out there, also thanks for the correction.