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64.13.14.96
In Reply to: RE: You don't want to short inputs... posted by Steve Eddy on July 25, 2007 at 16:43:11
Steve,
I admit to not having tried it, but it seems unlikely in the extreme that they would make any difference except in very special cases, the special case that comes to mind being a very near field source of intense noise voltage. The thing is, most RCA jacks have the hot contact recessed about 1/4 inch. That combined with the outer shield and (excepting phono input) line input levels AND having the input deselected since it's not being used, would seem to make any problems unlikely.
Finally I've gotten around to the question: Why do you think them worthwhile?
Regards, Rick
Follow Ups:
If you select that unused input, is keep your piece from emitting 'open input hum'. Some gear will hum pretty loudly on an open input. Tube gear, which tends to have a higher value input load resistor for the preceding circuit, seems to be a little worse.
Aloha,
Poinz
Huh... that's interesting.
Would that be from an external source or internal? Having wasted my youth building electronics rather than chasing gals, I've built many tube amplifiers. I can't say that I recall any hum problems at normal volumes even though I always ran the filaments from AC. If the source was internal, putting open caps over the RCA jacks should have no affect anyway. Shorted ones naturally would help.
Regards, Rick
In my experience, shorted or capped inputs reduce RF pick up, and considerably so if you live in a noisy RF environment as many of us do.
Cardas makes a nice set of caps, BTW. They work well because you can use them anywhere, inputs or outputs. For digital and video outputs, I generally short the center pin to ground via a 75 ohm resister. That seems to help limit the amount of RF they put out. I do that because of the large amounts of plastic on the components' backing these days. If yours has a decent amount of metal, I suppose the caps will work just as well.
Stu
I'll be darned, guess I'll have to give them a try. I ran across a small bag of them a while back that must have come with some piece of gear so I'll keep an eye out for them. Have you heard overt differences?
Output terminations are a different matter and make a lot of sense. I don't THINK I've got any open...
Rick
Well, I wouldn't consider the sonic differences earth shaking, but you do have to short or cap all inputs and outputs. For inputs, the RF can enter through the ground circuit if left uncapped.
Actually, I consider it better to address the various jacks on the digital and video sources first. Since many of those outputs are live, they are actually radiating a lot of RF and creating havoc with the rest of your analog gear. Try finding a cap for your S-video jacks, though......and.....take a gander at the number of fittings on a new TV set or on a A/V receiver!
RF sources these days are proliferating very rapidly. Even the LED displays will emit RF. I discovered that by accident when experimenting with some lead sheeting. A sheet in front of my CD player's display noticeably increased detail, you can easily check this out as some players have displays which can be turned off.
Capping a few inputs or outputs may not amount to much, but if you zealously do all, then the improvement becomes more noticeable. I like the Cardas caps, but sometimes I use those el cheapo IC's and simply short them out or buy those really cheesy RCA's and solder them closed (those all metal ones for like 5 cents each looking like refugees from the 50's ). The good thing about those caps, in general, is that it keeps the RCA jacks from corroding.
Stu
For inputs, the RF can enter through the ground circuit if left uncapped.
It's the center pin that the RF couples to. What the caps do is effectively shield the center pin.
se
Somehow I got my thinking a little convoluted, no excuse.
A while ago, there was a brief thread on the ultra Tweeter operating in the mega and gigahertz range. There, the speculation was that RF was entering the amp through the feedback circut.
8^)
Stu
A while ago, there was a brief thread on the ultra Tweeter operating in the mega and gigahertz range. There, the speculation was that RF was entering the amp through the feedback circut.Bah! Don't need to go that high. I've found you don't need to go over much more than 100kHz or so. Check out my Ultra Super Tweeter tractrix wood horns. Still waiting for someone to make a driver for them.
se
I just ran this past my dogs and they are keen on the idea. With their extended hearing they've been looking for a little more bite in the upper octaves...
Rick
nt
Wasn't aware of the S-video caps. The BNC caps have long been standard for radio use, BTW, and you can also buy them (non audiophile, of sourse) terminated with a resistive load.
Stu
Lot of stuff nowadays has RS232 for remote control. Maybe not as important since they are not part of the audio circuit?
paranoid. Since they serve remote functions, they have to live!
8^)
Stu
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