What is that strange Neve ground wiring?

[Golgoth]

Hi everyone, the title says it all.

What is that kind of grounding where a wire is connected to ground on one side and just ends in a loop in shrink wrap on the other?

Thanks!

 

[ruffrecords]

They are called pig tails. It is an standard method of securely attaching a wire to the screen of a cable. The ones in your pic a a bit odd because the tails comes out the back (like it does on a real pig). Most people tend to bring the tail out the front and wire ir direct to the XLR pin1.

I am not sure if the ones in your pics are 100% original Neve work. Their soldering was normally much better.

Cheers

Ian

 

[Golgoth]

Hi Ian,

Thanks a lot for the info! The unit I am restoring has seen a lot of 'meh' work through the years I guess..

So is my understanding correct that the green wires pigtailed as such just end there in the shrink wrap piece?

 

[JohnRoberts]

I can't see what is going on under the shrink wrap, but many people float one end of cable shields to avoid connecting the two chassis grounds together. Stray ground currents can corrupt signal grounds. I don't know a specific name other than floating the shield end. There is a "hybrid" shield ground that isolated the shield through a small capacitor at one end so it is effectively grounded for RF frequencies, but open circuit at lower hum frequencies.

There is also a name for hum problems caused by grounding both ends of shields, "pin one problem".

JR

 

[Golgoth]

I can't see what is going on under the shrink wrap, but many people float one end of cable shields to avoid connecting the two chassis grounds together. Stray ground currents can corrupt signal grounds. I don't know a specific name other than floating the shield end. There is a "hybrid" shield ground that isolated the shield through a small capacitor at one end so it is effectively grounded for RF frequencies, but open circuit at lower hum frequencies.

There is also a name for hum problems caused by grounding both ends of shields, "pin one problem".

JR

That's very interesting! I might open one end to check for a capacitor.

 

[ruffrecords]

Hi Ian,

Thanks a lot for the info! The unit I am restoring has seen a lot of 'meh' work through the years I guess..

So is my understanding correct that the green wires pigtailed as such just end there in the shrink wrap piece?

No, the green wire is soldered to the screen/braid of the cable then insulated by the shrink wrp. We had a discussion about this a while back:

Pigtails

Cheers

Ian

 

[Golgoth]

No, the green wire is soldered to the screen/braid of the cable then insulated by the shrink wrp. We had a discussion about this a while back:

Pigtails

Cheers

Ian

That makes more sense! I took "floating" quite literally haha! I will read what you linked carefully, as I am not an expert in grounding. I am in the process of studying an Audience Reaction Mixer to restore it (I promise my soldering job will be better than what was done!), your help is precious to help me figure things out before starting to work!

Best,
G

 

[JohnRoberts]

In the first image I will speculate the wire is two conductor shielded with black and red signal leads. The green wire could be soldered to the shield (but I still can't see under the shrink tubing).

In the second image it looks like two conductor wire with green and blue signal leads. I don't know what the extra(?) green wire is doing. One guess is that it is soldered to a shield then floating and insulated, but another two conductor blue/green cable in the same picture does not appear to have a shield.

I have found you can see exactly what is happening by removing the shrink tubing.

JR

 

[ruffrecords]

Here is some general advice on terminating screens from the EMC point of view (which unfortunately applies even to purely analogue audio simply because of the sheer numbers of digital noise sources in existence today.

You will notice this talks a lot about 360 degree termination. We don't generally do that but I think I have heard of some Neutrik connectors that get close.

Cheers

Ian

 

[Golgoth]

In the first image I will speculate the wire is two conductor shielded with black and red signal leads. The green wire could be soldered to the shield (but I still can't see under the shrink tubing).

In the second image it looks like two conductor wire with green and blue signal leads. I don't know what the extra(?) green wire is doing. One guess is that it is soldered to a shield then floating and insulated, but another two conductor blue/green cable in the same picture does not appear to have a shield.

I have found you can see exactly what is happening by removing the shrink tubing.

JR

In the first image, the ground wire goes through each XLR input connector, then to chassis ground (as pictured) where they meet with the XLR output ground and PSU ground.

Here is a picture of the green wire of the second picture without shrink wrap, it's indeed soldered to the braid. I don't believe that this green wire is a signal lead wire.

 

[JohnRoberts]

Thanks, that looks like one conductor shielded (with Ian's pigtail).

I was confused by the two conductor cable in same picture using blue/green colored leads.

JR

 

[Newmarket]

Here is some general advice on terminating screens from the EMC point of view (which unfortunately applies even to purely analogue audio simply because of the sheer numbers of digital noise sources in existence today.

You will notice this talks a lot about 360 degree termination. We don't generally do that but I think I have heard of some Neutrik connectors that get close.

Cheers

Ian

Neutrik do an "EMC" XLR with integrated annular capacitor and also a ferrite bead in the mix.
They also used to do a proper "Digital" XLR that had full 360 degree screen connection but that appears not to be in the line up now.

 

[ruffrecords]

I found another reference to 360 degree bonding and also bonding the screen to chassis ar both ends. This one is authored by a top guy from CADAC.
.

Cheers

ian

(I took their original web page and converted it to pdf so it would not get lost in the future)

 

[ruffrecords]

In the first image, the ground wire goes through each XLR input connector, then to chassis ground (as pictured) where they meet with the XLR output ground and PSU ground.

Here is a picture of the green wire of the second picture without shrink wrap, it's indeed soldered to the braid. I don't believe that this green wire is a signal lead wire.

OK so it is clear the green wire is a regular pigtail connected to the cable screen.

What also seems to be happening is that a bare wire bus has been run to all the input XLR connectors pins 1 and the cable screens have been connected to this via the green wires. I have used a similar technique myself where I want to feed phantom power to a group of mic inputs. In the second picture you can see the right hand end of this bus is connected to a brown/grey wire that disappears off picture (presumably to the 0V of the phantom supply. For some reason the XLR to the right of this bus has a separate wire leading from its pin 1 and also disappearing off screen (this seems wrong to me). There is also another green wire from the same point that disappears underneath a black cable never to be seen again.

Cheers

Ian

 

[ccaudle]

They also used to do a proper "Digital" XLR that had full 360 degree screen connection but that appears not to be in the line up now.

Still on the web page:
Neutrik XCC series

I was a little sceptical of those connectors, the crimp just went over the top of the shield folded back on the cable insulation. If you look at good BNC connectors, they give you a metal ferrule to slide over the cable insulation so that you are crimping onto a firm and known diameter backing. Even F connectors used for consumer video have a smaller diameter metal ferrule which inserts inside the shield and insulation so that when you crimp it doesn't just crush the cable insulation down without making firm contact. I bought a couple samples of the Neutrik connector and tried cutting a small piece from brass tubing to slide over the cable before folding the shield back. That seemed to help, but was a lot of work and always seemed to me like something that Neutrik should have put in the bag with the rest of the connector parts. I assume they did not because the wide variety of cable sizes used with XLR connectors would make it near impossible to make just one or two ferrule sizes that worked for everyone.
Also note that only female contact connectors are available with crimp, the male end is not available.

 

[Ike Zimbel]

Often, if I am wiring something new and not sure if I want / need to terminate a shield at one end of a cable, I will dress it, but tuck it up under the heat-shrink / Hellerman sleeve and leave it un-terminated. That way, if it turns out that I DO need to terminate that shield, I do not have to re-do the whole end. At least one of the ends in your pics looks like it may have gone this way.

 

[Newmarket]

Still on the web page:
Neutrik XCC series

I was a little sceptical of those connectors, the crimp just went over the top of the shield folded back on the cable insulation. If you look at good BNC connectors, they give you a metal ferrule to slide over the cable insulation so that you are crimping onto a firm and known diameter backing. Even F connectors used for consumer video have a smaller diameter metal ferrule which inserts inside the shield and insulation so that when you crimp it doesn't just crush the cable insulation down without making firm contact. I bought a couple samples of the Neutrik connector and tried cutting a small piece from brass tubing to slide over the cable before folding the shield back. That seemed to help, but was a lot of work and always seemed to me like something that Neutrik should have put in the bag with the rest of the connector parts. I assume they did not because the wide variety of cable sizes used with XLR connectors would make it near impossible to make just one or two ferrule sizes that worked for everyone.
Also note that only female contact connectors are available with crimp, the male end is not available.

Thanks. So they have been updated / renamed since I was looking at them seriously 20+ years ago. AES-3 application although we didn't find them necessary at end of day.

 

[Newmarket]

I found another reference to 360 degree bonding and also bonding the screen to chassis ar both ends. This one is authored by a top guy from CADAC.
.

Cheers

ian

(I took their original web page and converted it to pdf so it would not get lost in the future)

Yes. That's s great article. I think I've previously linked to it on this site - or somewhere anyway. Not necessarily directly applicable to all users here but the principles are worth noting for all.

 

[Golgoth]

OK so it is clear the green wire is a regular pigtail connected to the cable screen.

What also seems to be happening is that a bare wire bus has been run to all the input XLR connectors pins 1 and the cable screens have been connected to this via the green wires. I have used a similar technique myself where I want to feed phantom power to a group of mic inputs. In the second picture you can see the right hand end of this bus is connected to a brown/grey wire that disappears off picture (presumably to the 0V of the phantom supply. For some reason the XLR to the right of this bus has a separate wire leading from its pin 1 and also disappearing off screen (this seems wrong to me). There is also another green wire from the same point that disappears underneath a black cable never to be seen again.

Cheers

Ian

Hi Ian,

Here is a better picture with the full view of what is going on! Let me know if you still can't see something properly.

The brown/grey wires are going to ground on the 18pin card edge holder's bracket.

I am in the process of dismantling everything to clean up the case and reorganize the components' layout to fit a second output stage for stereo tracking/summing. That could be the occasion to build a better grounding solution if something's not correct!

Let me also add that the box is line level only (31267s only), no phantom power involved/needed.

Best,
G

 

[ruffrecords]

Thanks for the updated picture. I can see it all now. The green wire that was confusing me was just another pigtail. I agree, it is a good idea to review the grounding scheme when you rebuild.

Cheers

Ian