Originally Posted by Tim Wiens
I have three sources feeding my KX-R. Trading the C5 for the DX-5 would bring that down to two. The other source is an HD TV tuner though. How should I connect it using an optical link as you suggest? I thought the KX-R isolates the unused components.
Isolating the video and audio systems is critical. If you don't do this, the audio won't sound as good as it should and the video won't look as good as it could. The biggest problem is that all video displays have switching power supplies that create noise on the ground of your system. As soon as you hook up any component to both your display and your audio system, you are in trouble.
When we built the Ayre D-1 DVD player ten years ago, we were the only company to figure this out. That product was basically two separate components in one chassis -- there was even a separate sub-chassis inside the main (video) chassis to shield the audio circuitry. By using opto-isolators to bring the digital audio signals to the audio section, we achieved total galvanic isolation between the video and the audio sections.
This worked great if you only had one video source -- the D-1. But as soon as you hooked up a VCR or other video source with common grounds, the video and audio ground were no coupled back together again. To combat this, we started designing preamps (and integrated amps) that switch the ground
connection also when selecting inputs. The only component that is connected is the one that is selected.
This goes a long way towards solving the problem. The only other company to do this that I know of is Levinson on their No.32 and No.326 preamps. But it doesn't solve it completely as even a few picofarads of stray capacitance can couple noise very well when the noise is in the 100 MHz region. But it does get you 80% or 90% of the way there.
So if you have additional video components and you want to get the absolute ultimate in performance, the best solution is to use an optical
digital audio output from the device and connect it to an audio DAC that has no connection to the video system.
The problem is going to get worse in the future, however. Why? In a word, HDMI. I don't know of any way to switch isolate HDMI inputs. None. I don't know how to switch the grounds. There is no opto-isolator that can operate at 750 MHz, I can tell you that right now. That is an order of magnitude faster than any isolator can operate.
So if you really want the best performance, at some point you almost need two audio systems. Most TV's have built-in speakers. Just let them handle the less critical things like "General Hospital" or whatever it is that people watch nowadays on cable. Then connect the DX-5 to your good audio system. Since it completely isolates the audio and video, then you are good to go.
Sorry for the rambling nature of this post. There are obviously several different ways to skin this cat. We are trying to make it as easy as possible to get good performance by just hooking things up, by isolating the inputs on our preamps and isolating the grounds on our video disc players. But since we don't make set-top boxes or VCR's or the standards for HDMI, there is only so much we can do. But if you understand the issues involved, you should be able to come up with one way or another to keep your audio and video systems isolated from each other.