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XLR IC, pin1 to shield on only one end?

post #1 of 14
2/20/10 at 12:47am
Thread Starter 
Building an XLR IC right now. I searched but I just want to confirm this. I only tie pin1 to the shield on one end right? Source end being the DAC? Which means only the female/dac XLR will have pin 1 to shield and the male/amp XLR's pin1 will be left alone?
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post #2 of 14
2/20/10 at 2:24am
That's correct as far as I know. The shield pin doesn't carry a signal at all.
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post #3 of 14
2/20/10 at 3:30am
It depends on the equipment that's connected to both ends of the cable. If the source and target are both truly "floating" differential, then pin 1 is nothing but a noise shield, and could be connected at one end only. Typically this type of devices use balanced line driver/receiver circuitry (e.g., DRV134/INA134 chips), or have a fully-differential topology (such as β24, some Nelson Pass stuff), or are transformer-coupled.

On the other hand, if either end of the cable is implemented by two ground-referenced circuits, then that ground must be connected at both ends in order for it to work properly. Examples of these are "4-channel" amps like the balanced β22, dynamid/dynamight, etc.
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post #4 of 14
2/20/10 at 6:50am
amb: Thanks for that info. So would it be worth my while investigating the type of balanced circuit used in my DAC and various amps before deciding to use a cable with connected or non-connected (shield-only) ground? The commercial cables I use (Van Den Hul) have a shield-only ground, but since I want another pair of XLR cables, I was thinking of DIYing some, so this would be an important question I have to answer. Also, what benefit of detriment might one experience using the wrong kind of cable?
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post #5 of 14
2/20/10 at 8:12am
I'm going to build a pair of xlr "Y" cables to use from my preamp to my two poweramps as I am biamping.

Could someone please give me the wiring instructions for building such cable using xlr's?

Thanks
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post #6 of 14
2/20/10 at 8:57pm
If the amp requires a ground reference from the source to establish where the "0" is between the hot and cold sides, lacking the ground wire would cause the amp not to work properly (possible distortion and hum).
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post #7 of 14
2/20/10 at 10:29pm
Wouldn't the input attenuator establish signal ground as the midpoint between the two phases of the balanced signal?
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post #8 of 14
2/20/10 at 10:51pm
Let's say you have a 4-ch balanced amp. If the balanced source's XLR pin 1 isn't connected to the amp's signal ground via the interconnect cable, then the input attenuator (i.e., volume pot) "ground" connection won't be connected to the source's ground reference either. Thus the amp's concept of "zero" reference would just be its own PSU ground, helped by the potential divider established by the hot and cold pot sections. That would act more like a resistor virtual-ground rather than being "anchored" to the source's real ground reference.
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post #9 of 14
2/20/10 at 11:37pm
I guess I'm just having trouble understanding the actual harm to proper functionality from that. Establishing a ground reference this way is perfectly fine for an input transformer with no center tap (cf. Jensen's application notes), so what is different in this case? Assuming no other ground paths between the two equipment (i.e. earth ground), of course.
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post #10 of 14
2/21/10 at 12:06am
Quote:
Originally Posted by Fitz View Post
I guess I'm just having trouble understanding the actual harm to proper functionality from that.
There isn't any.

There is no "ground" in a balanced interface. Only the differential signal that exists between pins 2 and 3.

se
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post #11 of 14
2/21/10 at 12:07am
Thanks for the replies.
How do i tell if the balanced inputs and outputs on my preamp and poweramps are "floating" or "grounded"?
My preamp is an Enlightened Audio Designs Theatermaster Ovation and my power amps are Rotel RB1080's

Thanks
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post #12 of 14
2/21/10 at 12:20am
If you have a meter that lets you check for continuity, you can check between the grounds of unbalanced inputs and the chassis to see if there's a DC connection of the amplifier's signal ground to the chassis.

se
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post #13 of 14
2/21/10 at 12:45am
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
There isn't any.

There is no "ground" in a balanced interface. Only the differential signal that exists between pins 2 and 3.

se
Well hell, now I gotta change my view on this just to be contrary to you, Steve.
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post #14 of 14
2/21/10 at 1:03am
Quote:
Originally Posted by Fitz View Post
Well hell, now I gotta change my view on this just to be contrary to you, Steve.
What, you thought I was going to make your life easy?

se
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