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

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

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."

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."

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."

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

In article writes:

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.

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.

That's something different, usually an alloy of silver and coppyer.

What they're talking about here is "silver-bearing" tin/lead solder.
Mostly it makes the joints look more shiny, and might be marginally
stronger when joining certain metals, and, as Scott has pointed out,
not in others. The difference is probably negligable though, since
you're supposed to make a good mechanical joint before you apply
solder. It's unlikely that a joint soldered with silver-bearing solder
would hold or pull apart under real world strain (such as yanking out
a patch cable by the wire as opposed to putting it in a laboratory
stress measurement setup) any differently than one with ordinary
tin-lead solder.

There are some things for which you want some silver in the solder.
Remember that soldering is a chemical process - you're creating a
solution at the joint, and when it cools, you have an alloy. If you're
soldering to a silver contact such as the ceramic terminal strips used
in Tektronix oscilloscopes in the high impedance tube days, ordinary
tin-lead solder will dissolve that silver layer deposited on the
ceramic and weaken or destroy the terminal strip. Those scopes always
had a little spool of silver-bearing solder of the proper alloy
mounted inside so that it would be handy for making repairs.

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.



--
I'm really Mike Rivers - )

We've got enough brain damage in our fambly.

ulysses


lol

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."