XLR Shielding

About 10 days ago I had an opportunity to record a young girl singer.  She sounded fabulous and I will eventually be releasing the recordings in various formats.  When gathering my gear together, I could not find the required TRS to XLR cable I need to connect my microphone preamp (an M-Audio DMP3) and the recorder (an Alesis Masterlink).  I quickly brewed up a cable.  Actually it wasn't so quick.  First I had to research the TRS and XLR pin connections (TRS is as intuitive as it seems--the tip is hot).  This was the first and only soldering job I've done all year, and I didn't do many last year.  I've never settled in with a good temperature on the RadioShack digital soldering station I now use, it's only a few years since I ditched my old Weller station with broken thermostat, so I even looked online for what temperatures other people use for Eutectic solder.  Just under 700F seems about right, or it could be over 700 if you have "confidence."  Actually it takes less than 400F to melt the solder, but the higher temps let you work quicker--which is better (better fast and hot than less hot and slow).  This was all being done in the wee hours of the morning, 2-4am, with the recording scheduled for the next day at 1pm (an early hour for me).  I made the cable, and then found I had done it completely backwards so I had to take it all apart and put it back the right way.  Finishing just before 4 am.  Whew!

Actually what I did was to cut a 6ft TRS to TRS, and solder in an XLR.  But if you look at the official AES recommendation (as written up by Rane), it appears that a TRS to XLR should be wired lifting the shield at the XLR end.  (This is very strange and seems to deviate from all their other recommendations.)  I wired pin 1 to the shield, which I measured at being connected to the TRS sleeve.

I just ordered a new TRS to XLR cable from Sescom through Markertek…it will be interesting to see how they do it.

Turns out there is even some controversy about the AES recommendations regarding XLR to XLR.  Generally they recommend wiring 1 to chassis ground and not to signal ground, on both ends.  Nelson Pass says flatly that he is not an AES member and he does not follow their recommendations.  He wires 1 to signal ground.

Pass highlights the comments to the AES48 specification by Kim Rishoej and Svend Aage Christensen.  Their comments do make considerable sense (as compared with the AES broadside that if you do things their way, there will be no problems).  They suggest an alternative 4 wire approach.    Unfortunately I have not been able to obtain their actual specification for that.  However a common practice--for those not following AES48--is to connect pin 1 to the connect shell and ground both to chassis ground using a small capacitor.  This provides RFI shielding but blocks large currents from flowing in the shield.  Wikipedia describes this version.