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In Reply to: Re: Jon, thanks and here are some things I'm sorting through posted by Jon Risch on November 30, 2006 at 19:42:19:
Outside of that, have you ever experimented with resistively terminating your digital cables? Once you go this route, you'll understand how important VSWR / loading characteristics are at the RF frequencies that digital signals are transmitted at. I would be curious to hear your results if you have experimented with such things. Sean
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Follow Ups:
Yes, see:
DIY Cables and RFI/IGP
http://www.audioasylum.com/audio/cables/messages/80108.htmlCable RF Termination and Cable Loading
http://www.audioasylum.com/audio/cables/messages/80110.htmlI think that those will cover most of your concerns.
Sean, I haven't done digital cables. Only analog. That's why I'm asking these questions of Jon. The above is only what I"m gleaning from reading many posts here and elsewhere and I'm asking him if he thinks that's the right paradigm.Meantime, I'm not at all sure what you mean specifically by resistively terminating the digitals. If you mean adding a resistor somewhere somehow to try to match the impedance, I'd be very interested in how that's done. Do you know?
I have experimented under Al Sekela's tutelage with R-Cs on cable terminations of PCs and speaker cabling. But that's for RFI control, not necessarily impedance matching per se, though as I recall it is done because of impedance mismatches.
I'll do what i can to answer your questions Bart : )Resistively terminating a cable can be done two different ways. A common method is to place a resistor across the hot and ground connections at the load end of the cable. The resistor value chosen is typicaly the same as the nominal impedance of the cable being terminated. What one ends up with is that resistor tied in parallel across the input impedance of the device that the cable is terminated into. In most cases, this can help to reduce VSWR and signal based reflections from occuring. In some cases, this approach can load down the output stage of the source component, making things sound worse.
The other method involves much the same procedure, but uses a specific value resistor that is chosen based on not only the cable's nominal impedance, but also that of the input impedance of the terminating component. This approach can net even better results if the source component has a robust output stage, but in many cases, may result in worse sound. That is,in comparison to using either the cable alone or the resistive termination method mentioned above.
Stereophile had a brief article on this a few years back. There was supposed to be a follow-up article, but i never saw one. These approaches can work quite well at the component level, but should not be used on an amplifier / speaker interphase or power cord. This requires something different, which is probably what Al was helping you with. Sean
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