I dug out some CT100 satellite cable. It's lovelt stuff but it is far too stiff for my purpose because it unfortunately creates a real possibility of pulling out the plugs or altering their angle of entry which might create a noisy intermittent contact.
The general view (not necessarily the wisest view!) seems to be that for lengths less than 15 foot there is no advantage to using a balanced line. Here is what one such author states about it in a bit of a lighter hearted way than the others.
All audio equipment should adopt balanced working which would evade all such problems. The cost is minimal other than replacing the damned useless RCA 'phono' connector.
There are very many types of construction of shielding. The best consist of at least two layers.
Twisted pairs will only significantly help if your equipment is balanced.
Sorry, but this isn't something 'consumer audio' vendors give a damn about. They're only interested in liberating as much cash from your pocket as possible with inferior technology compared to what pros use.
I do understand (as John Larkin posted in this thread) that distance is my friend ~ to the power 4!
However, sometimes distance is hard for me to control. Even if I extend the length of the lead and try to reroute it the lead may still have to run close to potential sources of interference especially where it has to approach a device such as a PC to terminate its run.
On a related topic can I ask this ... if I have a stereo source then is it much better to use a twin cable in which each core has its own shielding than a cable in whch both cores are together and inside a single shielded?
Alas, I don't see that you have any practical alternative. No amount of filtering, shielding, or magic cable is half as effective.
Probably not. Many of us regularly use "twisted pair" shielded for L/R stereo. I just finished building eight 50-ft stereo mic cables with "star-quad" cable which has no shielding between the L/R pairs. I anticipate no significant issues with that practice.
Don wrote in news:Xns9BDC17F2C469E5D4AM2@69.16.185.247:
Yes. Small losses due to capacitance rarely matter in this case so close individual screens are good, and even over longer runs it's mainly an attenuation of higher frequencies well beyond those for audio except in runs of a hundred metres or more where it might best be considered differently.
You might lose signals to the other line causing crosstalk and reduced stereo width in much shorter runs if the channels are not screened from each other. It might not be significant but if for any reason you want one to be silent while the other is at full bore (studio effects and panning), it really pays to screen them separately.
I agree with (most) the other posters, ferrites are unlikely to help with a direct baseband audio signal being injected, and perhaps the easiest solution is use a longer cable that doesn't go as close to the CRT.
I'm thinking you could use audio transormers (which itself may be sensitive to the CRT's deflection coils from several feet away) at each end and run a balanced cable between them. "Star Quad" type configuration would be best to minimize/cancel interference. But all that gets expensive.
Another "expensive" idea - replace the CRT with one of the new-fangled flat-panel display things, surely they generate less interference, and they also take up less space.
Or move the CRT. Get a few phone books and/or encyclopedias to put under it and lift it up, just a few inches may help.
Reminds me of something that happened in the late '60s. I got dragged into a problem with a newly-commissioned ink drying oven on a web offset printing line. Temperature sensed with a type T thermocouple, driving a controller consisting of one of those "new-fangled" 709 op amp things driving a panel meter with another 709 as a comparator giving on/off set point control. Yes, they did things like that, back then.
The controller burst fired a 3-phase thyristor bridge, using, wait for it, unijunction oscillators. Whoever designed it (no names) must have felt mighty proud to be right at the cutting edge :-)
Problem was, the input 709 kept dying. It would run maybe half an hour, then poof. Maker's guy had been tearing his hair out for a week.
On the bench, the thing would run forever. Back on the machine, instant death. Voltages all within limits. It wasn't until I hefted a scope onto site to look at the supply waveforms that I found the tens of volts of common mode HF on the thermocouple every time the thyristors fired. Not only on the TC, on every bit of metal nearby. Ironically, the sales blurb claimed that it used zero-crossing switching and was RF immune, an absolute lie. (30 kilowatts, burst fired.)
Fifty cents worth of ferrite and ceramic caps cured it in half an hour.
--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)
I have seen this thread for a while without reading it. Because of it longevity I will throw in my 2¢ without even knowing what has been written in the past.
All the ferrite beads do is add lossy inductance to the common mode propagation along the vague transmission line formed by all of the conductors in parallel against free space and the surrounding environment. It is the equivalent of winding the cable on a transformer core. Ordinarily adding these beads will help primarily in two situations.
The receiving device is sensitive to common mode signals.
There is regeneration or parasitic circuitry that could cause oscillation to break out,
In the former, the inductance "chokes" the common mode. There are other ways of handling the problem. For example, coupling the audio signal, through an audio transformer to the receiving device will prevent the common mode signal from being transmitted.
For the latter, the beads introduce loss and change other circuit parameter. That may be enough to suppress oscillation.
If you can, understand what is going on rather than merely try anything.
Bill
--
Private Profit; Public Poop! Avoid collateral windfall!
Not all are mage the conductive plastic, but yes you can get it. You can also get aluminium film shields over a lapped one. Double shields too for that matter, one lapped in one direction, the other in the opposite.
Recalling an old trick/cure with low mv level magnetic pickups for record players - use two conductors inside a shield and ground the shield at one end only to avoid a ground loop. It works well for
60/120Hz and I see no reason for it not to work at audio frequencies. No guarantees but it is worth a try.
Hi Bill, thanks for the detailed info. You're right that I was guessing about the idea of using a ferrite without really knowing the theory! :-)
I was making my assumption based on my observation that all the USB leads which have come with my dictation machines or MP3 players have a plastic "blob" on them.
I was told this blob is a ferrite and that it's purpose is to prevent trouble from interference. I didn't get told if the blob prevented "incoming" intereference affecting the signals on its lead or, alternatively, if the "blob" limited "outgoing" interference being generated by using the lead. From what you say, I guess the idea of the blob containing ferrite is incorrect.
Perhaps the blob does not contain a ferrite but something else? So I dug around and got this interesting web page.
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"This cable has a blob half way along the cable that converts from USB to serial and then connects to the serial interface in the phone. The chip inside the cable is a Prolific 2303 and this is how your operating system will report it. It is marked as for the LG VX1/10 but works fine on the VX4400.
There's a chip in their blob? WOW. Well I never use my blob leads! I use just ordinary USB leads and there seems to be no problem.
Admittedly in this case the lead carries *digital* signals which go to the USB port. By contrast, I had been asking about *analogue* audio on a shielded lead going into the line-in socket of a PC (or perhaps going to some other device).
(a) So what is really in the blobs in my leads? (EG on my Olympus WS-331M) The above link talks about conversion to serial but I don't think my blobs would need to do that.
(b) Whatever is in the blob, would one of those help reduce interference on my intended longer leads because the leads will run near equipment and will carry analogue audio signals?
That's a great chart. I printed it out. I found my chosen suppliers didn't have several of the leads or even list Belden reference numbers in the same format as the table. Is the chart out of date?
After seeing your chart I went here.
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The Belden range is bewildering. Even the guides to cables are bewildering! For example:
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