HDMI Case Studies
Working with Distribution Amplifiers
Jeffrey A. Boccaccio is President of In-Visions Technology Inc., a consulting firm specializing in prototype engineering, new product development and marketing.
The Job
A sports bar installation with sixteen 1080p flat-screens, a Blu-ray player, and a cable box. The installer didn't have a single 1x16 distribution amplifier that could handle a system of this size, but he had a bunch of 1x2 DAs, so he decided to chain fifteen of them together into a tree structure. The second output on each 1x2 went into the next monitor, and so on down the line until he had everything hooked up. When he turned everything on, only four of his screens were functional. And he was lucky to get that.
The Problem
In a branch configuration like this, every stage multiplies your chances that something will go wrong. If this were analog video, it would be another story. But when you're moving data at Blue-ray rates, you need to understand the complexity of the interface before you start cascading DA's. Compounding the problem, some of the monitors were positioned 30-40 feet away from the source, others 10 feet away. So of course as he added more and more amplifiers, the integrity of the output degenerated as he got further and further out. Not knowing this, he put his longest cable runs on the last few amplifiers in the chain. And of course, the longer the distance, the more difficult it gets to maintain the integrity of the interface.
The Diagnosis
When I got the call, I explained to the installer that he shouldn't expect the output of each and every DA to be identical. They're not. We test them all the time and they're all over the map. This is true even if they're all the same model from the same manufacturer, or even when testing the different outputs from a single unit. I took one of these forty-dollar wonders apart once, just to see for myself, and discovered that (a) they hadn't packed the cables correctly inside, and (b) they'd done an incredibly poor job at screening the printed circuit board. Which is why all the outputs were so inconsistent. So depending on which one you hooked up to, and how far the monitor was from that output, some might work and others might not. When you start with a cheap product, then compound the problem by chaining fifteen of them together, it's a recipe for disaster. If he'd spent a few dollars more – pocket change on a job this size – and gotten a better quality DA, it would have been a different story.
The Workaround
Our installer is in a serious jam at this point. His client wants to open for business, and of course he wants to get paid. So I advised him to try reconfiguring so that his longest cables were hooked up to the closest DAs, and the shorter cable runs were on the DAs further down the chain. Under the circumstances, it seemed that this would give him at least a fighting chance. So he worked on this for two hours, making changes from one output to another output to another output, trial and error. And by the time he was done, he actually got all sixteen to work. Very lucky boy, I'd say. Until he got back to the shop and the call came in from the client: one display was out!
The Takeaway
Don't take the risk. Spend a little more and get the right products with the level of integrity that's needed for 1080p applications.
The views and opinions expressed herein are those of the author and do
not necessarily represent the views and opinions of HDMI Licensing, LLC,
the HDMI Founders or any of their respective parent organizations or
affiliates.