RGB Amplifier

[aut555]

I have built up a two transistor wideband amp. to boost a composite video signal shared by three outputs from a satellite receiver scart output which works fine. i.e. there is no obvious degradation. The alternative would have been to remove some/all of the 75 ohm trminating resistors in the shared receivers. The signal is AC coupled in and out. I have a 42" plasma t.v. with the primary input (again satellite) via a scart RGB input. The problem is that the maximum contrast is almost, but not quite enough which is irritating. I would like to use three of these amps for R G and B, but am not sure if the signal can still be AC coupled without losing proper black level. Any ideas?? Thanks for help

 

[Nigel Goodwin]

Should be no problem, RGB inputs are normally AC coupled!. I'm presuming your booster amp has a gain of two?, and 75 ohm resistors feeding each output?.

 

[aut555]

Nigel,
Thanks for the mega quick reply - I've never used a forum before - magic. Yes, it has a gain of two (all of which won't be needed of course) and yes the amp. currently working terminates into a 75 ohm resistor. I presume composite sync. will still need applying to pin 20 of the scart socket.
Many thanks for your help. Brian Adkinson

 

[Nigel Goodwin]

Nigel,
Thanks for the mega quick reply - I've never used a forum before - magic. Yes, it has a gain of two (all of which won't be needed of course)

Yes it will, the output resistor and 75 ohm load create an attenuator that divides by two, so your amp needs a gain of two to compensate for it.

and yes the amp. currently working terminates into a 75 ohm resistor. I presume composite sync. will still need applying to pin 20 of the scart socket.
Many thanks for your help. Brian Adkinson

Yes, apply composite sync as normal.

 

[aut555]

RGB amp

OK Nigel, read you loud and clear. Many thanks again, Brian