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I had recently purchased a Berhinger CT100 (mic/line tester); however, the manual is terrible and I am not sure exactly what the ground shield indicator does? I wrote Berhinger; however, I don't believe they answered my question. My Question is:

First, , let us say I am testing am XLR cable. Although there is no break in the pin signal, on some cables the "Ground Shield" light is illuminated and on others it is not. On other cables when I perform the manuals directions of "vigorously moving the cable" the "Ground Shield" LED light sometimes is illuminated and sometimes it does not. "What should it be doing?" "Should the 'Ground Shield' LED light be illuminated or should it not?" "If it is illuminated and then is not not when I touch it, is the cable damaged?" "If it is never illuminated, is it damaged?"

"Berhinger" response:
the XLR connector has 3 pins. It also has a "shell" - this is the cast aluminium casing which protects the whole thing from physical abuse, RFI, cyclonic weather systems, snowburn etc etc. The shell can also carry a potential. Usually the shell remains unconnected but can be soldered to the shield of the cable should the circumstances require. This makes in total 4 separate connections.

pin 1 - (audio) earth - not necessarily the same as chassis earth - may be
"isolated" or "floating"
pin 2 - positive phase signal
pin 3 - negative phase signal
pin 4 - shell - which, when connected to "gear", also makes contact to chassis earth- on equipment with a metal chassis.

The mic cable itself only has 3 connection possibilities - in most situations you want to keep the various chassis earths of all "gear" separate - whereas a consistent audio earth is more or less essential. For this reason it is conventional to connect the cable shield to pin 1 and not to the shell.

However - if the situation deems it necessary - you can solder the cable shield to the shell of the XLR connector. This connects audio earth to chassis earth. But this is not always desirable (it may give rise to hum problems).

The CT100 allows you to check whether or not the shell is connected to pin 1 of the XLR connector - and if it is - the CT100 also allows you to check for eventual
intermittent contact problems (bad soldering)

Thanks for any Help,


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mdemeyer Thu, 02/02/2006 - 17:12

I think their answer is clear. The light checks for a connection between the shell of the XLR connector and pin 1 of the XLR (signal ground). In all of my cables and experience, I always leave the shell un-connected. Sometimes if the solder work is poor (or there are stray strands of the cable shield roaming about in the connector), you will have an intermittent connection between pin 1 and the shell of the XLR. I'd consider anything like that to be a bad cable - open up the shell of the connector and fix it.


RemyRAD Thu, 02/02/2006 - 18:46

I have encountered more hum problems, from tying pin 1 shield to the XLR shell and don't recommend it, to begin with, it's not necessary. Nice that Beringer put that feature in however.

Too many connections
Ms. Remy Ann David

NoviceAtBest Fri, 02/03/2006 - 04:43


Thank you so much for your help! Seriously, I fell into this site a couple of weeks and have been reading both of your responses to different topics non stop. Tremendous help and much appreciated. You definitely know how to break down and simplfy a problem.