PC Engine Duo RGB video noise related to power adapter used

[Ziggy]

In an amp like that you're always gonna have a ground connection and a voltage connection.

Here, check out a different example of essentially the same thing:

Also, you might be able to understand your amp a little more if you read about voltage dividers.

Lastly, check out a really simple transistor amp like this one or this one. Or read the Wiki page for transistors. You know what's funny, the example amp on the Wiki page looks very similar to the amp you're looking at.

[kamiboy]

Yeah, I knew about transistors needing a voltage and ground connection.

What I found strange was the connection between 5V and video input before 5V and Video in are fed into the transistor.

Thanks for setting my mind at ease.

Oh, by the way, a 12V PSU works fine with the Duo in case anyone wanted to know.

[ApolloBoy]

The 5V is used to power the transistor in each circuit, and you're always supposed to have your video outputs grounded.

[kamiboy]

Yeah but look at the diagram, 5V has a connection not just to collector, but also to the video input pin (base), and video input has a connection to ground. I already know how a transistor is supposed to work, so I found those additional connections to be puzzling.

In any regard, I made that so called sophisticated AMP and, what do you know, the image quality is just every bit as rubbish as with a much simpler AMP I built before it.

The image is a bit blurry, most of which I discovered to be caused by those 10uf capacitors, it is also a tad too dark and there is some colour bleeding on the edge of pixels.

With this I am convinced that the problem was not with amp design since the simpler amp gave me the same picture, more or less.

Could the problem be with the quality of the transistors?

They were pretty cheap and chinese. I cant imagine a part with decades of history could have much of any swing in quality no matter who is making it, but just to make sure I'd like to ask whether anyone ever came across bad transistors, quality wise.

These say C1815 on them which I assume is the same as 2SC1815.

[ApolloBoy]

I tried that amp and never got it to work. Try this one instead, courtesy of micro on NFGGames:



I have this amp in my Duo-R and TG-16 and it works wonders. Fairly easy to build too, I use a SOIC-8 adapter board with the THS7314 and then I add the components around it.

[kamiboy]

Yeah, I already have the parts for that amp on order as a backup plan. I actually have everything in hand except for the SOIC to DIP-8 adapter which should be with me in a week or two.

I just dont understand why those other amps produce such a subpar result when they are so popular.