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#1
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Brad Harper wrote:
I was inquiring about having a 12 channel snake built for an upcoming live jazz show shot on HDTV. I requested that it be built with Canare or Mogami quad cable to a length of 100 feet. The person told me that they only used Mogami three conductor cable for long snakes because the quad cable doesn't sound as good due to the capacitance of quad cable over 100 feet. I have used 600 feet of Canare DT12 cable before, but of course I have never had the opportunity to A/B the signal to standard mic cable. The issues of RF resistance have always been the main concern. What opinions do you guys have on this. I actually don't have an opinion, but I do have the facts required to form one. You can calculate the exact effect of the cable capacitance yourself. Here's what you do: Look up the cable capacitance in the manufacturer's spec sheet. The lowest spec I know of is Belden 1800F which is about 13pF per foot. The highest of any reputable brand for mic cable is probably going to be about 60pF per foot for star-quad. Multiply this by the length of the cable and you'll have a s figure for the "shunt capacitance" hanging across each microphone output as a result of the cable. This may not be the only shunt capacitance, since many mike preamps evade good anti-RFI practices by hanging a capacitor from each input lead to chassis ground. But I digress. Suppose you have 100 feet of cable with 60pF/ft capacitance. That's 6000pF total, or .006µF, or 0.000000006 FARADS of capacity. This capacitance will interact with the impedance of the circuit it's in (the source impedance of the microphone in series with the cable's resistance and in parallel with the preamp's input impedance). This will generally be approximately equal to the microphone's output impedance alone, so you can just use that. The nominal value for most microphones is 150 ohms, but a modern transformerless condenser microphone will be much lower and an old transformer-coupled ribbon mike will be a lot higher. Now you can use these numbers to calculate the frequency at which you have a -3dB roll-off (it gets worse than that as you go up in frequency). The formula is: f=1/(2¼ZC) [frequency equals the reciprocal of the product of two times pi times impedance times capacitance] Using 150 ohms and 6000pF capacitance, we get a -3dB point of 176.8kHz. Doesn't seem like a problem to me. But imagine if you double the source impedance, doubled the cable length, and doubled the cable capacitance. You'd be down to 22kHz like that. And though you may NOT double all those things, you should realize that running multiple low-pass filters (which is what this is) in series will have the exact same effect. So although a single 176kHz LP-filter may not be audible, a bunch of them at various places in your signal path will be. So it's something to keep in mind. Exactly where this becomes worth sacrificing time, money, or other performance parameters is something I don't have a fully developed opinion on. ulysses |
#2
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I am talking about running a 50-100' snake in addition to the 15-25'
lengths on stage. I have used Canare or Mogami quad cable since 1986, but have never taken the time to A/B it to three conductor cable. A snake made from 3 conductor cable would definitly be less expensive as well as easier to obtain as long as RFI will not be a concern. Who knows if it will or not until after the purchase is made and we are off and running. I don't really think there will be any problems in this venue, so if everyone thinks that the sound quality would be improved by not using quad cable then I would be inclined to build some additional cables from Mogami three conductor to use on stage instead of my normal quad cables. I will be using Schoeps and Neumann condensers, Beyer and Royer ribbons, and a few dynamics as well as Radial active DIs. I will also be using two Cooper Sound mixers linked together which have Jensen transformers and very quiet high gain mic pres. Now would all this make an audible difference or am I just spending money and time? Brad Harper "Justin Ulysses Morse" wrote in message ... Brad Harper wrote: I was inquiring about having a 12 channel snake built for an upcoming live jazz show shot on HDTV. I requested that it be built with Canare or Mogami quad cable to a length of 100 feet. The person told me that they only used Mogami three conductor cable for long snakes because the quad cable doesn't sound as good due to the capacitance of quad cable over 100 feet. I have used 600 feet of Canare DT12 cable before, but of course I have never had the opportunity to A/B the signal to standard mic cable. The issues of RF resistance have always been the main concern. What opinions do you guys have on this. I actually don't have an opinion, but I do have the facts required to form one. You can calculate the exact effect of the cable capacitance yourself. Here's what you do: Look up the cable capacitance in the manufacturer's spec sheet. The lowest spec I know of is Belden 1800F which is about 13pF per foot. The highest of any reputable brand for mic cable is probably going to be about 60pF per foot for star-quad. Multiply this by the length of the cable and you'll have a s figure for the "shunt capacitance" hanging across each microphone output as a result of the cable. This may not be the only shunt capacitance, since many mike preamps evade good anti-RFI practices by hanging a capacitor from each input lead to chassis ground. But I digress. Suppose you have 100 feet of cable with 60pF/ft capacitance. That's 6000pF total, or .006µF, or 0.000000006 FARADS of capacity. This capacitance will interact with the impedance of the circuit it's in (the source impedance of the microphone in series with the cable's resistance and in parallel with the preamp's input impedance). This will generally be approximately equal to the microphone's output impedance alone, so you can just use that. The nominal value for most microphones is 150 ohms, but a modern transformerless condenser microphone will be much lower and an old transformer-coupled ribbon mike will be a lot higher. Now you can use these numbers to calculate the frequency at which you have a -3dB roll-off (it gets worse than that as you go up in frequency). The formula is: f=1/(2¼ZC) [frequency equals the reciprocal of the product of two times pi times impedance times capacitance] Using 150 ohms and 6000pF capacitance, we get a -3dB point of 176.8kHz. Doesn't seem like a problem to me. But imagine if you double the source impedance, doubled the cable length, and doubled the cable capacitance. You'd be down to 22kHz like that. And though you may NOT double all those things, you should realize that running multiple low-pass filters (which is what this is) in series will have the exact same effect. So although a single 176kHz LP-filter may not be audible, a bunch of them at various places in your signal path will be. So it's something to keep in mind. Exactly where this becomes worth sacrificing time, money, or other performance parameters is something I don't have a fully developed opinion on. ulysses |
#3
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Brad Harper wrote:
On a different note, I am making up some 5' Mogami patch cables to feed the DA-78s. Does anyone mess with silver solder or is everyone using tin/lead? Silver solder is essential if you're working on silver-plated connectors. It's not a good idea if you're working on nickel-plated connectors. 63/37 is still your best bet there. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#4
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Justin Ulysses Morse wrote:
Scott Dorsey wrote: Silver solder is essential if you're working on silver-plated connectors. It's not a good idea if you're working on nickel-plated connectors. 63/37 is still your best bet there. Why is that, Scott? I know why silver solder is necessary on solver and gold contacts, but how could it hurt to have it on your nickel? The joint isn't as strong. Cohesion between the surface and the solder isn't as good as it would be with 63/37. The 2% silver solder I use for everything is great (even though it comes from radio shack) and I haven't found any reason not to use it. What subtle calamity am I overlooking? It's not terrible, but it doesn't flow as well as 63/37, it's not eutectic so it's harder to make a good joint with it, and in the end the joints aren't quite as strong. And it costs more. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#5
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Mike Clayton wrote:
Folks, I need education here. I am confused about reference to silver solder - my experience thereof is as a high melting temperature (~600°C) alloy of silver and something else used by jewellers and plumbers and the like to make high shear strength joints in close fitting non-ferrous metals. Now you guys aren't talking about that, otherwise you'd be melting cables and components in all directions. What's your definition of silver solder, as used for electronic wiring and why might it be better than ordinary rosin cored lead based solder? He means "2% silver-bearing solder" which has a much lower silver content than jeweler's solder. You need to use it when working on silver-plated items, because using regular tin/lead solder will cause the plating to leach off into the joint. The 2% silver solder has enough silver in it already to prevent that from happening. We use it on little SMT jobs, and on big transmitting tube sockets, and all kinds of other silver-plated things. The local electronics store will carry it. Now that SMT is everywhere, it is becoming fairly common. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#6
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Mike Clayton wrote:
Folks, I need education here. I am confused about reference to silver solder - my experience thereof is as a high melting temperature (~600°C) alloy of silver and something else used by jewellers and plumbers and the like to make high shear strength joints in close fitting non-ferrous metals. Now you guys aren't talking about that, otherwise you'd be melting cables and components in all directions. What's your definition of silver solder, as used for electronic wiring and why might it be better than ordinary rosin cored lead based solder? The stuff I get from Rat Shack is 62/36/2, rosin-core. I like the way it flows, I'm used to it, so I use it for everything. They also sell lead-free solder, which is I think just silver and tin, but that costs a lot more and doesn't flow well at all. Though if I ever hire my little brother to do assembly work, I'll probably make him use it. We've got enough brain damage in our fambly. ulysses |
#7
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#8
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We've got enough brain damage in our fambly.
ulysses lol |
#9
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In article znr1057232374k@trad, Mike Rivers wrote:
And then there's the lead-free solder that a lot of health and environment conscious manufacturers are using now. There may even be state laws that require it. You can get that at Radio Shack too. As I recall, it has bismuth (or is it antimony?) rather than lead, probalby just as hazardous in the landfills, but at least handling it or breathing the fumes all day won't give you lead poisoning. Give 'em a little time and they'll figure out that it's hazardous to your health too. It's actually probably nastier for you than lead. The fumes from soldering have no lead in them. The rosin probably isn't great for your lungs, but the lead doesn't evaporate. The fumes from the organic flux IS definitely really bad for you, because of all the acids in it that are no fun to breathe in. But some places are required to use it, because with that stuff you can deflux in a big dishwasher rather than using nasty solvents for defluxing. In general, I think the "lead-free" and organic rosins are a really bad idea for small shop use although I can see the need on big fab lines. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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