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What I hope to be an exhaustive thread on soldering Gotham GAC-3. - Gearspace.com
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What I hope to be an exhaustive thread on soldering Gotham GAC-3.
Old 12th March 2010
  #1
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grrrayson's Avatar
 
🎧 10 years
What I hope to be an exhaustive thread on soldering Gotham GAC-3.

I'm getting ready to make some microphone cables with GAC-3. The official recommendation is to solder the shields together with the ground pin but I've read of various approaches.

My questions at this point:

Do any of you have direct experience with soldering the shield elsewhere?

How exactly should one solder the shield to the shell if one were to do so? One big gob of solder somewhere in the XLR barrel sounds like it could get messy. Is there any particular technique regarding tinning the connector? Should the two shields be soldered at different points? I've heard the Klaus Heyne method is one shield to ground and one shield to the shell–might this have disadvantages in some scenarios?

I've done searches but not found anything as straightforward as I'm asking for here.

At this point, I plan to make my cables the specified way (shield to ground pin), but two with shield to shell and two with the shield split so I can compare for myself if and when I come across a noisy scenario.


I've made my own cables for a long time but I'm not rich in my understanding of electricity–input would be greatly appreciated.

Regards,

Grayson
Old 12th March 2010
  #2
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🎧 15 years
A straight-up mic cable needs pin 1 to pin 1 continuity - whether you get it with the third conductor plus the shield telescoped or continuous is up to you.

Neutrik establishes shell connection with a spring loaded terminal, switchcraft through the set screw/terminal.

Don't bother making the shell connection - the equipment you terminate to will make this connection if deemed appropriate.

Clamp on ferrite chokes installed on a one-turn loop of mic cable will probably do more to reduce interference than expensive mic cable - the served or braided shield of nice handling stage cable actually shields less completely than the foil shield of cheap install wire.
Old 12th March 2010 | Show parent
  #3
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🎧 10 years
Quote:
Originally Posted by ripple_fx1 ➡️
Don't bother making the shell connection - the equipment you terminate to will make this connection if deemed appropriate.
Good point–I do realize this.

So then why are there advocates of alternate shield configurations? I'd love to hear the science from both sides.

Also, I'm guessing you don't have any experience with the GAC-3 yourself–feel free to correct me if I'm wrong!

Thanks for the response.
Old 12th March 2010 | Show parent
  #4
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🎧 15 years
You're not wrong - never used or even seen it. I'm interested to hear what others have to say as well. Guessing there may be slight advantages in fixed installation interconnect, but not with a live production rig or simple microphone cable, where not adhering to the tried and true can quickly become a mess.
Old 12th March 2010 | Show parent
  #5
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Radardoug's Avatar
 
🎧 10 years
I have known situations where direct connection between the connector metal and pin1 has caused problems in cables. Shure used to supply their mike cables wired this way, and one pa firm I worked at always broke this connection. Strictly speaking as soon as you plug the plug in it should get a ground from the peice of gear with the chassis connector, but of course this does not cover cable to cable connections.
Old 15th March 2010 | Show parent
  #6
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Before addressing the question, please allow me to mention that we (Studio Electronics) are now the Western U.S. distributor for Gotham audio cable. I had been fan of Gotham cable since the 1980's and was glad to accept when Gotham offered me the position last year. Our site now has a Gotham page at Gotham Cable - Studio Electronics Burbank Ca and all their cable products are on our web store.

The question about shield wiring is a good one and different opinions have been expressed over the years.

The Old Neumann / Gotham recommendation specified that shields be soldered to the shell connection point. So, if you wire according to that recommendation, the XLR's will look like this:
Brown = Pin 2 + (Hot)
White = Pin 3 - (Cold)
Green = Pin 1 (Ground)
Both Shields to Connector Shell and Jumper to Pin 1 (or) Split Shields between Pin 1 and Connector Shell

This wiring applies for all connections on all sides of the connectors (M & F). (Remember that these recommendations assume the cable is being used as a microphone cable. In line level applications, grounding the shields to the connector shell is rarely needed, and may cause ground noise problems.)

The advantage of connecting the shield to the shell on both ends is that it may prevent RF pickup. The disadvantage is that on line level cables, it may introduce hum. (This is true with any kind of cable -- not just Gotham.) for line level applications it may be best to try both ways, and see which works best for you.

After posting this reply, I contacted Klaus Heyne to ask his opinion on this. Klaus emphatically replied that for mic cables "Cable shield and cable ground (where provided, as in GAC 3) must be connected to pin 1 on both connectors AND to the sleeves (metal housings) of BOTH connectors."
Old 16th March 2010 | Show parent
  #7
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grrrayson's Avatar
 
🎧 10 years
Thanks-this is basically the same information I have re: Klaus.

I'm very interested in there being such divided camps here.

So: 1. What's the science behind the times this reduces RF and the times it causes hum?

2. How predictable is it?

3. Does Klaus himself keep around a few regularly wired cables for the random times the shell-connected shielding might cause hum?


I do of course value praxis over theory and once again will make variations myself, but I like to have as much understanding as possible. (And I'm still waiting on connectors before I make these cables anyway.) I suppose I just need to delve into some deeper electrical study when I have the time.


Thanks again so far for the input-further accounts of personal experience still greatly appreciated.

Regards,

Grayson
Old 16th March 2010 | Show parent
  #8
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🎧 15 years
The shell-to-shell grounding method generally reduces RF because it gives a more complete ground connection that links all the chassis together. It's a little hard to explain but by "unifying" the grounds and enclosures you wind up with better RF immunity.

In cases where the mic has its own power supply, this method can sometimes cause a ground loop. What happens mic power power supply will have a little bit of capacitive and inductive leakage between the AC line and its audio ground, as will the preamp. There will tend to be a slight AC voltage difference between these two points and when they are connected together by the shield in the mic cable, a very small amount of 50/60 Hz. current may flow through the shield. This small current may find its way into the preamp and show up as hum. (This will not happen with dynamic or ribbon mics since they have no power supply.)
Old 18th March 2010 | Show parent
  #9
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🎧 15 years
Here is my paraphrased response to David's inquiry he had sent me:

Quote:
We have to make a distinction between interconnecting studio equipment situated AFTER the microphone in the recording chain, and connecting audio to microphones.

There is no debate that when terminating 3-pin XLR cables used on microphones, cable shield and cable ground (where provided, as in GAC 3) must be connected to pin 1 on both connectors AND to the sleeves (metal housings) of BOTH connectors.

With other words, in order to suppress any form of RF or other stray noise into the cable, the shield must extend from the very tip of the microphone (i.e. its metal head basket/housing) to the metal connector plugged into the mic pre (where it is then hopefully integrated into that equipment's shielded environment.) If that scheme is not strictly followed, the microphone, as the endpoint (better: starting point) of the wired connection, will act as an antenna and transmit RF or RF hash into the audio.

This wiring scheme for microphones, long advocated and implemented by Neumann and other major mic companies, is indisputable. The confusion has always been around ground/shield connections on interconnect cables connecting between two components downstream from the microphone, as this can SOMETIMES induce a ground loop when one or both AC-powered components are not properly grounded.

But I have found that it is prudent to always start with the most RF-tight scheme first, even when using an XLR cable as interconnect between components. Only when ground hum is audible should the shield connection to chassis ground be broken, and only on ONE end of the cable, usually on the downstream end.
There is no case I have ever heard of where ground hum would be caused by the above mentioned scheme in phantom-powered mics. Likewise, in all the years I have connected the shield and ground as mentioned in tube mic power supplies, no one has ever reported any ground loops either.

Best regards,
Klaus Heyne
Old 18th March 2010 | Show parent
  #10
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grrrayson's Avatar
 
🎧 10 years
The man himself!

Klaus:

Thank you so much for the elucidation. That helps a lot.

Case closed!

Grayson
Old 23rd April 2010 | Show parent
  #11
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Delta Sigma's Avatar
 
🎧 10 years
From my experience in communications: a shield should only be connected at one end of a cable.

We use this method for T1 wiring, shielded Cat5, serial cables, etc.

The big difference I see is that if a common return is needed it will be a pin on your connector attatched to a conductor (though not always). The shield is not used as a return but rather as RF shielding.

As mentioned above, a mic cable uses the shield as a conductor which is used for Phantom power and to give the mic a ground reference.

Interconnecting two peices of equipment can get tricky though (as explained above. All equipment most likely will have the same reference form the power source's earth ground so interconnecting cables can add a second path to ground creating ground loops.

I like the method of leaving the interconnecting cable's ground intact and lifting it if there is a problem.
Old 23rd April 2010 | Show parent
  #12
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🎧 15 years
Quote:
Originally Posted by Delta Sigma ➡️
From my experience in communications: a shield should only be connected at one end of a cable.
Lifting shields at one end has it's place in certain situations. But a shield connected at one end is most definitely an antenna and can result in demodulation in high RF environments.

Back to the Gotham cable and tying the shield at the ground pin rather than pin 1. Acceptable yes, but the integrity of the XLR case to XLR case connection is definitely inferior to the actual pin contacts. For that reason, I've always modified Neumann mic cables so that the shield and green were soldered to pin 1 only. Furthermore, it eliminates the possibility of a ground loop occurring should the XLR case touch a grounded device (at the bottom of a rack or out in the studio).

The effects of a large one turn transformer (loop of cable to and from connected equipment) is often mistaken as a ground loop.
Old 25th April 2010 | Show parent
  #13
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MicDaddy's Avatar
 
🎧 10 years
most of the time the equipment I use, pin one is tied to the chassis of the microphone.

I've found many times, poor contact with set screws (where pin1 was jumped to set screw) of connectors to case parts of the microphones causing static/hum/pops.

I've also ran into many condensers that do not tie pin one to the chassis, but it is used as 'circuit common'.

ground is what we walk on....
Old 27th August 2010 | Show parent
  #14
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JoFo's Avatar
Quote:
Originally Posted by David Kulka ➡️
Before addressing the question, please allow me to mention that we (Studio Electronics) are now the Western U.S. distributor for Gotham audio cable. I had been fan of Gotham cable since the 1980's and was glad to accept when Gotham offered me the position last year. Our site now has a Gotham page at Gotham Cable - Studio Electronics Burbank Ca and all their cable products are on our web store.

The question about shield wiring is a good one and different opinions have been expressed over the years.

The Old Neumann / Gotham recommendation specified that shields be soldered to the shell connection point. So, if you wire according to that recommendation, the XLR's will look like this:
Brown = Pin 2 + (Hot)
White = Pin 3 - (Cold)
Green = Pin 1 (Ground)
Both Shields to Connector Shell and Jumper to Pin 1 (or) Split Shields between Pin 1 and Connector Shell

This wiring applies for all connections on all sides of the connectors (M & F). (Remember that these recommendations assume the cable is being used as a microphone cable. In line level applications, grounding the shields to the connector shell is rarely needed, and may cause ground noise problems.)

The advantage of connecting the shield to the shell on both ends is that it may prevent RF pickup. The disadvantage is that on line level cables, it may introduce hum. (This is true with any kind of cable -- not just Gotham.) for line level applications it may be best to try both ways, and see which works best for you.

After posting this reply, I contacted Klaus Heyne to ask his opinion on this. Klaus emphatically replied that for mic cables "Cable shield and cable ground (where provided, as in GAC 3) must be connected to pin 1 on both connectors AND to the sleeves (metal housings) of BOTH connectors."
If anyone would be so kind as to post pictures of this...

I've got some GA3 I'm soldering right now, and honestly I can't quite tell if I'm doing it right. How do I solder the ground and the shield to both the chassis and pin3?

The terminated Cables I originally received from Gotham (to test) have both the ground and shield soldered all to pin 3.

thanks
Old 28th August 2010 | Show parent
  #15
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Klaus's Avatar
 
🎧 15 years
Unless your cable was wired the way you described it on purpose, for a specific (rather odd) set-up, I would say it was simply wired wrongly, and will not work in any studio or live sound interconnection scenarios that use XLR-3 connectors.

The international standard for XLR 3-terminated cables is:

Pin 1 Cable shield (plus ground conductor, on 3-conductor cables, like GAC 3)

Pin 2 Audio (+)

Pin 3 Audio (-)
Old 24th November 2011
  #16
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jackinthebox's Avatar
 
🎧 15 years
how about experiences using Neutrik NC3MXX-EMC Nickel EMI Protected Professional 3 Pin XLR Plugs?

They have a ferrite bead and a circular capacitor for extra EMI shielding.

And they cost four times as much as a standard connector......

I have just become a UK dealer for Gotham GAC-3 and GAC-7 and i will be manufacturing cables for sale. Would there be demand for a very highly shielded cable with these connectors?

jack
Old 2nd November 2017 | Show parent
  #17
Deleted b69c0aa
Guest
Quote:
Originally Posted by jackinthebox ➡️
how about experiences using Neutrik NC3MXX-EMC Nickel EMI Protected Professional 3 Pin XLR Plugs?

They have a ferrite bead and a circular capacitor for extra EMI shielding.

And they cost four times as much as a standard connector......

I have just become a UK dealer for Gotham GAC-3 and GAC-7 and i will be manufacturing cables for sale. Would there be demand for a very highly shielded cable with these connectors?

jack
Hi Jack, how do you wire GAC3 and the EMC connectors?

...what I do is solder the ground to the top of one of the cups and then spread the shield around the cups as usual...it actually makes them a bit easier to put together (as one of those fiddly cups is now held in place). I wonder should I make a better connection between the ground conductor and the shield though.

Some discussion here: http://www.neumann.com/forums/view.p...key=1326109089
Nothing definitive re EMC.
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