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[Dave Potter]

XLR;
pin1 screen
pin2 hot
pin3 opposite polarity

I was recently looking at an early 80s amp which used pin3 as hot with pin 2 unconnected. As far back as I can remember (1987) pin2 was hot. A work colleague of mine mentioned that he thought that Europe had the pin2 as standard while USA was pin3 ... or it had just changed .... or something.  so;

When did we all agree that pin 2 is hot?

[Art Welter]

Pin 2 to 3 hot was all over the place in the late 1970s through the mid 1980s. Towards the late 1980s it seemed to settle to pin 2  positive or "high". I never liked the change, it was simpler to wire unbalanced adapters with pin 3 hot.

Someday TRS inserts may have a universal code followed also.

Always a good idea to do polarity checks with older mics and amps.

[Geoff Doane]

My memory is a bit foggy on this, but I think it was at the LA AES show in 1988, that one of the handouts at registration was a little card with a spinning arrow, that pointed to either pin 2 or 3 as "hot".  In other words, there was no AES standard yet.  I think by the next time the show was in LA (1990), pin 2 was the accepted standard.

The first piece of gear that I encountered in my pro audio career that made a difference, was a Shure M67 mixer.  It had XLR ins and outs (at mic level), but you could switch them to higher level and unbalanced, and in that configuration, the XLRs were pin 3 hot.  So for that reason, I standardized my own rig on pin 3, wherever I could.  Of course that gradually changed over the years.

GTD

[trace knight]

I remembr back in those dayz...........some amps, i think I saw it on a carver, and a crest had a recessed switch pin 2-3 swap on the back panel, they couldn't make up thier minds I guess!
tk

[John Roberts {JR}]

Dave Potter wrote on Fri, 18 January 2008 02:32

XLR; pin1 screen pin2 hot pin3 opposite polarity I was recently looking at an early 80s amp which used pin3 as hot with pin 2 unconnected. As far back as I can remember (1987) pin2 was hot. A work colleague of mine mentioned that he thought that Europe had the pin2 as standard while USA was pin3 ... or it had just changed .... or something.  so; When did we all agree that pin 2 is hot?

Depends on who you consider "we" to be.

I used to write a magazine column back in the '80s and did a survey of manufacturers in the early '80s. The results were quite mixed with no real pattern other than perhaps most new companies (new in '80s) were pin 2 hot. There were established Brit and US companies in both camps. My understanding is there was an early (IEC?) pin 2 hot standard that most manufacturer's followed for microphones, but line level XLR interfaces were mixed with companies trying mainly to remain consistent with themselves. A little odd but some companies were pin 2 hot on mic XLR while pin 3 hot on line levels.

In the mid-late '80s IIRC AES published a standard defining pin 2 hot, which for many people was their first awareness of any standard. For some larger companies (like the one I worked at for a while) this was a struggle as bringing new product up to the AES standard makes you inconsistent with (in some cases) decades of existing product. But it was the right thing to do, so most companies now adhere to the AES standard.

There is some legacy gear floating around still in use that will be pin 3 hot, so this can always reach out and bite us in unbalanced or mixed wiring interfaces.  

Perhaps, significant to this time line, discussion and increased awareness for the importance of maintaining absolute polarity occurred at least in the wider recording press around this time (early '80s). PA and recording were always aware of relative polarity, but absolute polarity was dismissed by many as being inaudible, until proved at least for certain types of waveforms.

JR

[John Roberts {JR}]

trace knight wrote on Fri, 18 January 2008 10:42

I remembr back in those dayz...........some amps, i think I saw it on a carver, and a crest had a recessed switch pin 2-3 swap on the back panel, they couldn't make up thier minds I guess! tk

The pin hot selector switch was one way to support customers with predominantly pin 3 hot systems, while also working with pin 2 hot system.

I encountered customers who were extremely confused and sometimes over reacted to mixed standard situations. In some cases customers introduced a polarity reversal with their modified wiring "fix"  where there wasn't a problem, thanks to the symmetrical nature of differential in and differential out interfaces.

I'm glad this is mostly behind us.

JR

[John Nobile]

I'm not sure what happened at Soundcraft. I have a 500 with pin 2+ and an 8000 which came out later, with pin 3+. Any Soundcraft I've used that was newer than the 8000 was pin 2+ .

Did pin 3+ become standard in England for a while? Or just Soundcraft?

[John Roberts {JR}]

John Nobile wrote on Fri, 18 January 2008 13:07

I'm not sure what happened at Soundcraft. I have a 500 with pin 2+ and an 8000 which came out later, with pin 3+. Any Soundcraft I've used that was newer than the 8000 was pin 2+ . Did pin 3+ become standard in England for a while? Or just Soundcraft?

From memory pin 2 or pin 3 hot was mixed even among Brit companies. There was plenty of speculation about pin 3 being a Bit standard or US standard, but my research at the time turned up no real national patterns, just random before a certain time period, and mostly pin 2 hot after that time period.

JR

[Lester Moran]

John Roberts  {JR} wrote on Fri, 18 January 2008 17:39

I encountered customers who were extremely confused and sometimes over reacted to mixed standard situations. In some cases customers introduced a polarity reversal with their modified wiring "fix"  where there wasn't a problem, thanks to the symmetrical nature of differential in and differential out interfaces.

My KT DN 360s are "pin 3 hot".  My Ramsa WRS 840 is "pin two hot", but more importantly, the individual send and return insert points on the mixes are tip=hot, ring=cold.  If I present the inserted EQs with the Ramsa's hot signal to pin 2 of the EQs, I get 6 db loss, as compared to presenting the Ramsa's hot signal to the EQs at pin 3 (which introduces no loss).  Do you know why this would happen?...  i.e. what might be peculiar to the DN 360 balancing scheme to make it "care" whether the hot signal ran through it at pin 3 as opposed to pin 2?

Thanks,
Les

[John Roberts {JR}]

Lester Moran wrote on Fri, 18 January 2008 14:49

My KT DN 360s are "pin 3 hot".  My Ramsa WRS 840 is "pin two hot", but more importantly, the individual send and return insert points on the mixes are tip=hot, ring=cold.  If I present the inserted EQs with the Ramsa's hot signal to pin 2 of the EQs, I get 6 db loss, as compared to presenting the Ramsa's hot signal to the EQs at pin 3 (which introduces no loss).  Do you know why this would happen?...  i.e. what might be peculiar to the DN 360 balancing scheme to make it "care" whether the hot signal ran through it at pin 3 as opposed to pin 2? Thanks, Les

I'm pretty sure that particular product's quirks wrt to pin 2/3 hot have been well explored on this site so I suggest a search specifically for that discussion. As i recall pin 3 hot wasn't the only issue.  

The general answer is a TRS insert is converting a balanced or differential 3 circuit signal to a single ended 2 circuit signal, and then back again. Sh__ happens, between different pin 2/3 standards, and more importantly between different 3 circuit output topologies in such mixed 3 circuit to 2 circuit interfaces.

Rane also has a pretty good wiring guide on their website for working with sundry interface topologies.

JR