XLR connector wiring

[STC]

According to my amplifier's guide the proper wiring for my preamp to amplifier is to have the XLR cable pin 1 NOT connected to pin 1 at the amplifier end. Unless, the source is 2 wire AC supply the pin 1 should not be terminated to pin 1. I checked my two reference cable and it was connected pin to pin. What should be the correct way to do the wiring with the Motu to Crown using Phoenix connector. Currently, they (Mytek to Crown) are connected wrongly but nonetheless,  working perfectly.

 

Anyone here having hum problem could share the details here? 

[One and a half]

This Rane paper is an invaluable reference for connecting different audio components together, includes XLR, TRS, RCA and various combos thereof.

[STC]

I was relying on Rane’s paper but the Crown amplifier guide is different. 

 

 

All main equipments are 3 wired AC connection. By right it should be connected as in the following diagram. 

 

 

 

[mjb]

XLR Pinout:

 

Pin 1 = Cable Shield/Ground

Pin 2 = Signal Positive 

Pin 3 = Signal Negative 

 

If both ends are fully balanced you don‘t necessarily need pin 1, and adding it may introduce a ground loop. However, the cable may benefit from a grounded shield, in which case you may connect pin 1 at one end only.

 

If you‘re converting a single ended to balanced, pins 1 and 3 would be bridged. Pin 2 carries the signal.

 

[One and a half]

@STC, do you have a meter? Please measure pin 1 resistance to the chassis on the crown (with the AC plug removed).

Pin 1 should be the same resistance on all inputs to the chassis.

[STC]

25 minutes ago, One and a half said:

@STC, do you have a meter? Please measure pin 1 resistance to the chassis on the crown (with the AC plug removed).

Pin 1 should be the same resistance on all inputs to the chassis.

 

It is so difficult to acces. I am not sure whether the right is pin one or the left. Anyway, the right pin is in kilo ohm and the left is 80 ohm. I wasn’t expecting this unless the screw to the chassis is not connecting to the chassis. 

[esldude]

7 hours ago, STC said:

 

It is so difficult to acces. I am not sure whether the right is pin one or the left. Anyway, the right pin is in kilo ohm and the left is 80 ohm. I wasn’t expecting this unless the screw to the chassis is not connecting to the chassis. 

You may have a resistance balanced connection instead of full differential.  This isn't all that uncommon.  One pin is used for the signal, but the other goes through a resistor to ground and doesn't really get used.  You still get some of the resistance to common mode noise pickup from balanced connection.  

 

Try swapping the red and black leads of your multimeter and re-measure.  The kohm side will probably stay the same.  The 80 ohm side will likely be much higher or perhaps show no connection.  The side staying the same is going thru a resistor.  

[STC]

5 hours ago, esldude said:

Try swapping the red and black leads of your multimeter and re-measure.  The kohm side will probably stay the same.  The 80 ohm side will likely be much higher or perhaps show no connection.

 

I think my meter is broken. On closer look there is a space between 8 and the next number in the display. It looks like pin 1 should be 1  Ohm or less. 

[STC]

Just found out that the Crown XLS is "electronically balanced" XLR input. That probably explains the different methods used in RANE and Crown. Not sure of Motu's type. 

 

 

[Speedskater]

The XLR pin 1 is the shield (not the balanced signal ground). In a chassis connector, the pin 1 should be attached to the chassis at this connector.  There are situations where the cable pin 1 is only connected at the powered send end. Often a hybrid connection is made at the cable receive end. This hybrid connection is a small RF capacitor connecting the shield to pin 1.  A direct connection should be used with microphones, battery powered units and maybe 2 wire AC powered units.

Going balanced to unbalanced, confuses things because the chassis shield needs to become a signal ground.

[mav52]

When all else fails, Call Crown and ask them.

 

Crown,

Technical Support

844-776-4899

[mansr]

5 minutes ago, Speedskater said:

The XLR pin 1 is the shield (not the balanced signal ground).

Balanced signals don't have a ground.

[Speedskater]

8 hours ago, mansr said:

Balanced signals don't have a ground.

Exactly!

[STC]

Since there is no hum with my current connection will just connect them as it is and will only disconnect the shield pin if necessary. Thanks guys but it looks like we should pay more attention to the proper termination to isolate hum.

[marce]

17 hours ago, mansr said:

Balanced signals don't have a ground.

But they do have a return path?

[biosailor]

17 hours ago, Speedskater said:

The XLR pin 1 is the shield (not the balanced signal ground). In a chassis connector, the pin 1 should be attached to the chassis at this connector.  There are situations where the cable pin 1 is only connected at the powered send end. Often a hybrid connection is made at the cable receive end. This hybrid connection is a small RF capacitor connecting the shield to pin 1.  A direct connection should be used with microphones, battery powered units and maybe 2 wire AC powered units.

Going balanced to unbalanced, confuses things because the chassis shield needs to become a signal ground.

I don't quite understand the distinction between chassis connection and shield (pin 1). Can someone enlighten me?

[marce]

Chassis is generally the case and as such is part of the shielding, so the cable shield should connect preferably for a full 360 degrees to the chassis either directly with metal to metal or via a ring of capacitors to provide a low impedance connection for RF.

There is a wealth of information on shielding from the likes of Henry Ott, Ralph Morrison, Rane, numerous AES publications etc. and despite some views on this forum to the contrary, plenty of research, experimentation and information on shielding.

[biosailor]

1 hour ago, marce said:

Chassis is generally the case and as such is part of the shielding, so the cable shield should connect preferably for a full 360 degrees to the chassis either directly with metal to metal or via a ring of capacitors to provide a low impedance connection for RF.

There is a wealth of information on shielding from the likes of Henry Ott, Ralph Morrison, Rane, numerous AES publications etc. and despite some views on this forum to the contrary, plenty of research, experimentation and information on shielding.

With chassis, do you mean the case of say, the amp? Don't XLRs touch with their own case the case of the equipment chassis? Sorry for asking annoying questions!

[marce]

Usually yes the case and the chassis are the same, depending how the connectors are configured they may or may not be touching the case, though they should be.

Here is some info from Rane regarding all this.

http://www.rane.com/note110.html

https://www.rane.com/note151.html

Bill Whilock:

http://www.bennettprescott.com/downloads/grounding_tutorial.pdf

and this one from THE EXPERT (maybe more should read his stuff on shielding)

http://www.hottconsultants.com/pdf_files/aes-2007.pdf

There is more but these are the standard references. Anything you don't understand I or others should be able to help.

 

[biosailor]

50 minutes ago, marce said:

Usually yes the case and the chassis are the same, depending how the connectors are configured they may or may not be touching the case, though they should be.

Here is some info from Rane regarding all this.

http://www.rane.com/note110.html

https://www.rane.com/note151.html

Bill Whilock:

http://www.bennettprescott.com/downloads/grounding_tutorial.pdf

and this one from THE EXPERT (maybe more should read his stuff on shielding)

http://www.hottconsultants.com/pdf_files/aes-2007.pdf

There is more but these are the standard references. Anything you don't understand I or others should be able to help.

 

Thanks so much for the references, greatly appreciated! I'll look them up and happily return for questions! Thanks!

[Speedskater]

On 6/5/2018 at 2:48 AM, marce said:

But they do have a return path?

Say what marce?

But we have to be careful about what we speak.

There are:

a] complete balanced interconnect systems

b] balanced interconnect cables

c] internal (within a component) balanced circuits.

[Speedskater]

On 6/5/2018 at 3:03 AM, biosailor said:

I don't quite understand the distinction between chassis connection and shield (pin 1). Can someone enlighten me?

With chassis, do you mean the case of say, the amp? Don't XLRs touch with their own case the case of the equipment chassis?

There should be no difference. pin 1 should be attached to the chassis at the connector. (that's within 1 inch/2 cm)

However the shell of a cable XLR connector is not connected to the shield in the pro world.  Because the shell of a portable cable could come in contact with a metal object at a different potential.

But from a theoretical point of view, it would be better if the shell was part of the shield system.