Video Amplifier
IMPORTANT: The current version of this amp is designed
to be connected to a VGA card which outputs 5 volts on pin 9 of the VGA
connector. Older VGA cards may not have this facility. We still have some of
the older manually-wired version which can be separately powered. Email for
further info. If you are not sure, have a look at the connector on the VGA
card. If one pin is blanked off, then this amp cannot be used without manually
wiring to a 5 volt supply. See below for instructions.
This is a
standalone video amplifier which converts the 1 Volt output from a VGA card
into 4 Volts required by most arcade monitors.
The circuitry is exactly
the same as that used on the J-PAC and uses a high-bandwidth video amplifier
chip. It provides an easy way of fixing a "dim" arcade monitor installation by
boosting the signal input to the same level as a "real" game board.
The amplifer contains four channels,
Red,Green,Blue and Sync. The Sync is a buffer rather than an analog amplifier,
and this is to avoid the "fold-over" at the top of the picture on some monitors
that are sensisive to DC input levels.
Installation:
Identify the R,G,B input wires to
the monitor. These are often actually coloured Red,Green,Blue.
Identify the
ground wire to the monitor, and composite sync.
Cut these wires and strip.
Connect the monitor R,G,B, Sync and Ground wires to the "OUTPUT" terminals of
the amp.
The amp comes with a cable to connect to the VGA card.
Almost all monitors, even those which have separate V and H sync
inputs, will work with composite sync (generally connected to the H input) A
few monitors may need separate H and V sync though. In this case the syncs can
be separated by doing the following:
Identify the location on the PCB marked
"CUT for H/V"
Cut through the short section of track between the two
"half-moon" shapes.
Connect the monitor vertical sync to the connection
(white terminal block) marked SYNC
Connect the monitor horizontal sync to
the connection (white terminal block) which is unmarked.
Wiring to a
5 volt supply This step is NOT needed for ArcadeVGA or any new VGA card.
This is only needed if your video card does not output 5 volts on pin 9 of it's
connector. All currently-produced cards do send 5 volts on this pin so this
step is only needed with older cards such as ATI Rage 128.)
Locate a 5 volt
supply, for example from the header connector on the I-PAC (see
I-PAC page for pinout) or from
the PC game port or a drive power connector etc. Don't use a mains adaptor,
these do not give a stable enough output. Connect the ground from the supply to
the GND white terminal block connection. Solder the 5 volt wire to the PCB pad
indicated by the arrow on the picture below:
