Buzz in the microphone. Microphone cable running from an RE20 into a Symetrix 528e. To get from the microphone, to the 528e, mic cable is about 10' long. Mic cable runs past, and through, a number of AC cables and power supplies (yes I'm aware that audio cables should be as far away from AC cables and power supplies as it they can be, but when you've got a tight studio, you can only do so much). Tried all kinds of esoteric mic cables to try and get rid of the buzz. I tried 1) Gepco XB201DBM (double braided) 2) Belden 1800F AES/EBU 3) Belden 1696A AES/EBU (braid & foil). All had the same buzz. Yes, if I moved these cables around a bit, the buzz sometimes changed, and once, almost went away. Then I thought, for the heck of it, let me try some basic shielded balanced line level cable (Clark Wire & Cable RS22G-R/G), and weave it through the exact route all of the other just mentioned cables picked up the buzz. Guess what...no buzz at all. What the heck.
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Microphone Cable Buzz
- Thread starter Brian Bowers
- Start date
No need to lift the ground on the 528e, as this is not a ground loop problem. With the microphone, and microphone cable, disconnected from the 528e, there is no buzz. This is a cable performance problem/issue. What I'm pointing out is that these cables, with their fancy heavy duty shielding (double braid), and foil braid combo, were not able to reject the electro-magnetic fields around them, as well as the Clark cable was. From my simple little test, the Clark cable gave me the lowest amount of buzz (none), of all the cables tested, running the exact same route. I was surprised, and wouldn't expect that from a cable with only a foil shield. I should mention that shields were terminated at each end of the XLR connector (soldered to pin 1). This is a quote from the Clark's website for this cable:
Excellent common-mode and RF/EMI noise rejection are achieved by a precision twisted pair and 100% foil shield.
...of course, but every other cable manufacturer also typically has the same claim. Unfortunately I did not have the length of Canare quad cable on hand to be part of the test. I should point out that the Clark RS22G2-R/G that I'm referring to, is a stereo/dual cable. I split it, and was using only half of it for this test. Capacitance for the Clark cable is respectable. Some will say that the best common mode rejection will be achieved by the twisting of the pair, and not necessarily the shield.
Excellent common-mode and RF/EMI noise rejection are achieved by a precision twisted pair and 100% foil shield.
...of course, but every other cable manufacturer also typically has the same claim. Unfortunately I did not have the length of Canare quad cable on hand to be part of the test. I should point out that the Clark RS22G2-R/G that I'm referring to, is a stereo/dual cable. I split it, and was using only half of it for this test. Capacitance for the Clark cable is respectable. Some will say that the best common mode rejection will be achieved by the twisting of the pair, and not necessarily the shield.
But... You won't have a ground loop if the cable isn't terminated at both ends. That's why they call it a ground loop.
Not to be old-school nit picky; but your terminology from your original post should have said you had a hum, not a buzz. In the audio world the term buzz is 60hz or 120hz electrically audible noise typically from a ground loop. A hum, which in the case of your microphone cable issues, is caused by an inductive field near the cable, and varies as the cable is moved around. Then there are microphonic tenancies of the cable too, where if you move the cable around, the microphone preamp actually picks up and amplifies the movement.
They're correct. Common mode rejection is best achieved with tighter and more frequent twists in the plus and minus conductors.
Canare cable isn't intended to be stereo cable. All Canare mic cable is that way. They add the second set of conductors for better common mode rejection. Double the conductors, four times the common mode rejection.
Take a look at a piece of CAT5 vs. CAT6 network cable. The main difference is the number of twists in the cable.
K
kf4rca
Guest
At one station I worked at, I found that I had to use transformers to clean up the input signal. We were in a high RF zone and the equipment had high speed op amps for the input that amplified everything. The buzz was actually sync buzz from one of the TV's on the candlabra.
If you could find them, the old phone company 111C transformers were seemingly the 'magic bullet' for getting RF or induced noise out of balanced audio.
K
kf4rca
Guest
Believe I used Triad A67J transformers. More space efficient.
Bell wrote the book when it came to transmitting audio over wires. They knew exactly how far they could go over a pair of #10 copper coated steel wires (what they started out with).
Those 111 coils are pricey on Ebay. You might as well go with the Triad or Jensen transformers. Op Amp Labs makes a nice plug-in version too.
I've got an old A2A transformer. That transforms 75 ohm video to 124 balanced video for transmission over their twinax system. Yep, they were pumping video around on poles. But it was only good for 5 miles or so. But they use fiber optic for that today.
Now as I recall Cat 6 is shielded and Cat 5 is not. The only reason Cat 5 works well for data is because of the FEC (forward error correction) that analog audio does not have.
Bell wrote the book when it came to transmitting audio over wires. They knew exactly how far they could go over a pair of #10 copper coated steel wires (what they started out with).
Those 111 coils are pricey on Ebay. You might as well go with the Triad or Jensen transformers. Op Amp Labs makes a nice plug-in version too.
I've got an old A2A transformer. That transforms 75 ohm video to 124 balanced video for transmission over their twinax system. Yep, they were pumping video around on poles. But it was only good for 5 miles or so. But they use fiber optic for that today.
Now as I recall Cat 6 is shielded and Cat 5 is not. The only reason Cat 5 works well for data is because of the FEC (forward error correction) that analog audio does not have.
No. Cat 5E and Cat 6 cable are both un-shielded by default, although shielded cable is available for an upcharge.
The main difference between Cat 5E and Cat 6 cable is the wire gauge - 24 AWG vs 23 AWG, and some manufacturers insert a spacer between the pairs. This results in less capacitance per meter, which improves bandwidth.
Further, standards-compliant 100-BASET and 1000-BASET Ethernet do not use FEC. Packet errors are detected by a checksum embedded within each Ethernet transaction, but if FEC is desired it must be done at a higher layer than Ethernet.
Cat 5 and 6 cable is perfectly fine for audio transmission. It's quite handy for certain situations with balanced audio because it is readily available, cheap, and the color coding can make mistakes fairly obvious.
The main difference between Cat 5E and Cat 6 cable is the wire gauge - 24 AWG vs 23 AWG, and some manufacturers insert a spacer between the pairs. This results in less capacitance per meter, which improves bandwidth.
Further, standards-compliant 100-BASET and 1000-BASET Ethernet do not use FEC. Packet errors are detected by a checksum embedded within each Ethernet transaction, but if FEC is desired it must be done at a higher layer than Ethernet.
Cat 5 and 6 cable is perfectly fine for audio transmission. It's quite handy for certain situations with balanced audio because it is readily available, cheap, and the color coding can make mistakes fairly obvious.
True, and the shield on CAT 5 or 6 cable is mainly useful in situations where cable will be running near large inductive fields. Like big electric motors or transformers. It doesn't make any difference in shielding RF effectively. Usually a couple torroids inserted in the long runs to block RF from skin effect along the cable works much better and less expensive.
And something which the firmware or application generally does, not a data transmission standard.
Radio Systems really brought the use of Ethernet cabling/RJ45 connectors into the balanced audio world. In fact; they just recently announced that they were closing down for good.
K
kf4rca
Guest
Ethernet Z is 100. Broadcast audio is 600. BUT, there are a lot of Pro-Audio stuff being used in the broadcast arena these days. And they have an input Z of 10K.
I can see where unshielded cable would be a problem with an input Z of 10K. Especially if you have a 50KW ionospheric heater in the room next door!
I can see where unshielded cable would be a problem with an input Z of 10K. Especially if you have a 50KW ionospheric heater in the room next door!
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