Re: Interesting Circuit... Drive multiple monitors?

On 11 Mar 2007 15:15:14 -0700, in msg <et1v1i01cs0@xxxxxxxxxxxxxxx>, jrok
<jrokweb@xxxxxxxxxx> wrote:

In article Hans O says...

Not my sketch and I don't know the guy but it's an interesting circuit.
He's using a 4066 switch, pulling the ground Vss to -5, and using it to
drive multiple monitor from the same source. Use at your own risk but do
tell if it works.

This circuit makes no sense whatsoever. 4066 are not buffered, he's effectively
just shorting all the R,G,B,S lines together, respectively.

Heh.. an intesting idea, he's effectively using the 4066's as distribution
amps (!) Saves using an few op-amps and parts I guess, or just one 'big'
op-amp that can drive a few 75ohm loads ;)

Well, except the 4066 is not a buffer, just an analog switch, which in this case
he's has set to be always on. So the 4066 is acting like 4 80ohm resistors. He
be much better off just using 80ohm resistors, if that was his intent, they at
least would be a more linear, better freq response, etc.

However the 80ohms will also screw up the impedance matches needed to stop
reflections on the lines. He'd be better off just shorting all the lines
together, though that might overload whatever's driving the monitors.

If the monitors he's driving are terminated by the standard 75ohm resistor, then
the 80 ohms of the 4066 will act like half of a voltage divider and the video
signal will be at half level, and if it syncs up, it will be dim.

A plumbers analogy to this design would be to replace the waterlines going into
your house with a sprinkler control valves, and then wiring up all the valves so
they're on all the time. Sure, it would work, but why do it?

-Zonn
--
Zonn Moore Run MAME's vector games on a real
Zektor, LLC vector monitor using the ZVG!
www.zektor.com More info at: www.zektor.com/zvg
(Remove the ".EXAMPLE" from email address to reply)
.

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