Amiga Video Toaster
/ Flyer FAQs
Amiga Video Toaster
All Versions
"Bleed-through" or "CrossTalk" on Toaster
Product: Video Toaster
Platforms: 2000 3000 3000T 4000 4000T
Problem: Ghosted images of other
video appear in Toaster Main Output:
Situations which may cause 'bleed-thru' or 'cross-talk':
- badly shielded I/O video cables
- partially unshielded I/O video cables
- improper termination with either video or RGB buses
- bad RGB cable/port/monitor
- improper/nonexistent termination levels on the
source/record decks
- electrical ground loops
- (very rarely) Video Toaster card itself
If the equipment is otherwise ok then a ground loop
is the most likely culprit for this. The best way to
check this is to reduce the system to the simplest
setup. The computer system and a monitor for program
out, with the attached video equipment powered down,
detached, and unplugged, including the Flyer drives.
Boot the system up, run the software, select your framebuffer
with the logo on preview, then alternately select inputs
3 and 4 on your program out. If you do see ghosting,
isolate the computer itself by using two prong adaptors
on the RGB and the Program out monitors, and retest.
If you still see the ghosting, then you have a problem
either in the system or in the Toaster or Flyer. If
the Toaster or the Flyer is the source of the problem,
contact Tech Support for repair authorization.
If you see no ghosting, then the Toaster and Flyer
are okay. Down the system, add a component, and retest.
(Note: this procedure is similar to how you would test
for a faulty component which is feeding voltage or
signal into its chassis ground - a "ground fault".)
If you don't want to go through the entire painstaking
process of putting the system back together a piece
at a time to figure out the loop, you could simply
set things up so that only the the computer system
is grounded, and the attached equipment all goes to
a power strip (or several) which are not grounded,
plugged in using a two-prong adapter. This prevents
the possibility of a loop, and the video and audio
interconnections between the equipment cover the issue
of grounding on the attached equipment.
The Toaster exhibits only the same level of crosstalk
that, by the laws of physics, exists in any circuit
board. Any trace or wire produces a minute field, and
thus affects the signal in other traces or wires. In
normal operations this kind of "crosstalk" is
certainly not visible, and is most often undetectable.
Ground loops in particular have the capability to amplify
such crosstalk, and also to act as an antenna to pick
up RF noise in the environment and inject it into the
signal path.
Ground loops will thus also have an effect on the
video signal quality. The incoming composite video
on a Toaster BNC is by necessity referenced to ground
when it hits the first amp. If there is noise in the
ground, that noise is translated directly into the
video signal.
Ground loops are a fact of life for any electronic
equipment, particularly noticable in video and audio
applications; this is a fact of physics, not an error
in our engineering.
By its very nature, setting up any video system creates
ground loops. Take the example of a very simple Toaster
setup: The computer housing a Toaster, a destination
deck, and one monitor for each, one grounded power
strip. In examining just the computer and the deck,
we have the following connections:
Computer (power supply) to power strip --> this
connects the computer's chassis ground into the house
ground.
Deck to power strip --> this connects the deck's
chassis ground into the house ground.
Toaster to Deck via BNC video cable --> the shield
line on the BNC connects the chassis ground of the
Computer to the chassis ground of the Deck, and a ground
loop is thus created, circuiting around the deck, the
computer and the power strip.
As you add more components, each component creates
a loop each with every other component connected to
the power strip.
A ground loop will act as an antenna, picking up RF,
and is susceptible also to induced current from surrounding
magnetic fields. Again, this can amplify symptoms such
as crosstalk and introduce noise and interference patterns
into video equipment. The way cabling is arranged in
a suite can increase or decrease the problems, and
the condition of the cabling and other ground plane
problems may also have some effect.
In point of fact, when you set up a system with only
one item plugged into the ground, and the rest of the
items plugged in using an adaptor which lifts the ground
on the power cord, you are not ungrounding the equipment
at all. In both BNC and RCA cords (at least, the kind
of RCA cords you should be using), the shield ground
interconnects the chassis grounds of equipment they
link together, thus all interconnected equipment is
grounded, in series, through the one piece of equipment
that connects to house ground. All you have really
done is eliminate ground loops, not grounding.
By eliminating all those "unintentional antennas",
you should get cleaner signals throughout your system.
