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[Pars]

Yet Another XLR Question...

 

Building my first balanced amp, some connection questions:

 

What do you do with the shield? Reading the RANE app notes seems not appropriate for parts of this, since I am using 4-pin XLR, and the 3-pin standard has pin 1 as ground.

 

I am reworking the previous 4-conductore rewiring my phones right now, and chopped the previously wired 1/4" plug cable part way to wire in a 4-pin female/4-pin male (the male will be the main phone connector into a 4-pin female on the amp), turning this cable portion into an adapter for when I want to use the phones from an SE amp. The main cable terminates at the phones in a 4-pin mini XLR, in which the shield is not terminated. I assume use the telescoping shield philosophy and terminate the shield to the connector body on both std. 4-pin XLRs at the mid point?

 

For 3-pin XLR balanced amp inputs, just follow the RANE notes?

 

Describe how YOU did things

 

Also, on the balanced Dynahi SS thread, I see one amp using a male 4 pin XLR for the jack? Seems like a bad idea, and that the standard is (or should be), Male for inputs, Female for outputs?

Edited April 1, 2015 by Pars

[mwl168]

For my balanced headphone and headphone amps, I use male 4-pin XLR to replace the TRS plug and female 4-pin XLR for the headphone amp's balanced output. I would not call this configuration "standard" but rather it seems to be the "convention" I observe the commercial products seem to adopt. I agree it's controversial.

I have been studying the balanced signal wiring scheme recently as well. The way I understand RANE's paper, the cable shield should be connected to pin 1 of the plugs. But pin 1 of both the input and output chassis XLRs should be connected via a short wire to the chassis and NOT to the signal ground. Effectively making the cable shield an extension of the chassis.

I hope those with better and more knowledge and experience will chime in.

Edit: if I recall correctly, when I re-terminated the Cardas cable of my HD650, the cable is a 4-conductor construction with no shield. I simply soldered each of the conductors to one of the 4 pins of the XLR male plug.

Edited April 1, 2015 by mwl168

[Pars]

That was pretty much my understanding as well; the cable shield is part of the chassis ground, which may or may not be the same as signal ground.

 

I also recall ground loop interupters, such is what is used on my headamp Gilmore refererence board. Basically a low value resistor (4.7 ohms?) and a cap, tieing board ground to chassis. I don't see this done much anymore, unless I haven't been paying attention.

 

GND LOOP CAPACITOR      1       DIGIKEY EF4104

GND LOOP RESISTOR       1       MOUSER  280-CR5-4.7

 

EDIT: probably shouldn't have made the topic so cryptic
 

Edited April 1, 2015 by Pars

[Earspeakers]

Some sockets put shield automatically to socket body, and thereby immediate chassis ground. Neutrik generally has a tab to make it be your choice. Ideally you would run a ground wire to the star ground point. However, with any normal amp your star ground point will turn into a big enormous lump of solder, so cutting that down a bit helps. Second and perhaps more importantly, it is probably better to let the source ground the shield to not set yourself up for a potential ground loop. As long as one side grounds, it's good. Edit: I should say I don't know if that's any standard practice, but what I often do. Not sure it makes much difference in any case. The impedance of these cables isn't critical (i.e. 50 ohms) because it's all extremely low frequencies, and it's twisted triplet anyhow, so do what works for you. 

 

I worked with a guy who spent 10 years working on ground for a project (super high sensitivity measurement device). He used to say "there is no such thing as ground". 

Edited April 1, 2015 by Earspeakers

[gepardcv]

While we're on this subject, what is the correct wiring for 4-pin XLR headphone output jacks? I found this diagram: http://robrobinette.com/images/Audio/HiFiMAN_Pin_Diagram.gif

 

So pin 1 is L+, 2 is L-, 3 is R+, and 4 is R-. So far so good. But compared to the HeadRoom two 3-pin XLR jack guide, there is no chassis ground. Why not? Am I missing something?

[kevin gilmore]

and that's the problem. the 4 pin is balanced only, no ground.

 

can't be used on common ground headphones.

[spritzer]

Some of them have shield in the barrel but I'm not certain that all of them have it. 

 

5 pin would be better but thinner conductors means less bass molecules so nobody would do that. 

[luvdunhill]

Team 5 Pin checking in!