XLR Male input and wiring on a tube reel to reel

[Levente]

Hey Guys

I have an old tape recorder ( fully refurbished) with an XLR MALE ( yes male!) Microphone Input.

Believed to be a sensitive one 600 ohms (?) no schematic, just guessing.

This input goes to UTC transformer (unknown).

The wiring is interesting on the XLR input.

Pin 1 and 3 are connected together+chassis, and pin 2 looks like has a paint (black).

This means if I am correct that pin 2 is "hot" but why the pin 3 and 1 are connected to the chassis?

This is an old gear from the 50s/60s tube based circuit...i thought here we will have the old US pin configuration for pin 3 as "hot" and pin "2" cold.

Could you please advise on this? any hints would be greatly appreciated!

Thank you !

[Paul JD]

Standard XLR wiring for balanced input would be pin 1 = shield, pin 2 = hot, pin 3 = cold. If it is being used for unbalanced signals it is normal practice for 1 & 3 to be linked so that the shield is connected to the cold side. XLR mic input sockets would normally be female, are you sure it's not an output?

[Levente]

hey Paul, thanks.

It is definitely input...not sure why they've decided on a Male socket tho... also, that means this Mic xlr input is unbalanced?

[Craig Sawyers]

Looks as if it is wired to be unbalanced. Is there any evidence that is has been rewired by a dopey previous owner? If it is a transformer coupled circuit normally the two input windings would go to pins 2 and 3 of the XLR and nothing else. The transformer shielding can would go to chassis, as would pin 1 of the XLR. By as short a route as possible.

Looking at Wikipedia, Cannon invented it in the 50's as the Cannon X, then added Latching and it became the XL, then added Rubber insulation and it became the XLR.

So if your gear came from the 50's this would have been a very early use of a Cannon connector.

Craig

[John10b]

The Shure mics we use on stage all came supplied with XLR Male plugs, the reason I remember this is funny now, but at the time it wasn’t. On the stage we had installed about six XLR female sockets, with protective covers, however this didn’t prevent naughty teenagers sticking matchsticks into the sockets!!
I look back now and have a smile.
Cheers
John

[Levente]

Originally Posted by Craig Sawyers

Looks as if it is wired to be unbalanced. Is there any evidence that is has been rewired by a dopey previous owner? If it is a transformer coupled circuit normally the two input windings would go to pins 2 and 3 of the XLR and nothing else. The transformer shielding can would go to chassis, as would pin 1 of the XLR. By as short a route as possible.

Looking at Wikipedia, Cannon invented it in the 50's as the Cannon X, then added Latching and it became the XL, then added Rubber insulation and it became the XLR.

So if your gear came from the 50's this would have been a very early use of a Cannon connector.

Craig

Hey Craig,

Indeed! It is a Cannon connector...attached a couple pic's...it has not been messed around with (besides that it was fully refurbished by a lovely chap down in Sussex), I am sure he did not touch that connector.

I will have not used it since the refurb project fully,just tested with a dynamic mic...sounded better and louder when I switched the mic to HI Z ...

I was hoping to hook this up with my Bozak mono mixer (main XLR out which is also a male XLR)...and trying to find a way through that mic xlr input on the deck....(the bozak has either 200/ or 600 ohms output)

thanks for the feedback !

[Craig Sawyers]

That is a very early one - without the latching part.

Craig

[Herald1360]

Originally Posted by Paul JD

Standard XLR wiring for balanced input would be pin 1 = shield, pin 2 = hot, pin 3 = cold. If it is being used for unbalanced signals it is normal practice for 1 & 3 to be linked so that the shield is connected to the cold side. XLR mic input sockets would normally be female, are you sure it's not an output?

How can a "balanced" signal have hot and cold sides? Surely each side is equally hot (or cold) with respect to whatever it's balanced about?

[Levente]

Hey Herald, thanks for the feedback!

This means, it is a balanced connection? Just confused on why pin 3 is going to Ground/ Shield...

And the same is happening on my mixer monitor output (also early 60s) Male xlr. This mixer comes with an option where I can separate the pin 3 from the shield (pin1). That adds to my confusion more.

Attached a quick drawing of my mixer too I was hoping to connect straight into this old tape recorder mic input.

The mixer XLR output says 10V with 200Ohm Load... i think...but looking at the schma, no sure. (Does not have an output transformer)

[Paul JD]

Originally Posted by Herald1360

How can a "balanced" signal have hot and cold sides? Surely each side is equally hot (or cold) with respect to whatever it's balanced about?

It's common practice to refer to them as hot and cold, hot being the non inverted in phase signal and cold being the inverted out of phase signal. https://en.wikipedia.org/wiki/Balanced_audio

[Paul JD]

Originally Posted by Levente

This means, it is a balanced connection? Just confused on why pin 3 is going to Ground/ Shield...

If pin 3 is grounded then it is unbalanced. Balanced connections have 2 phases, a non inverted signal and an inverted signal, when pin 3 is grounded the non inverted signal is grounded out so you are only left with the non inverted signal i.e. unbalanced.

[Levente]

Thanks Paul, understand.

This is how it is inside the unit...

Pin 3 to chassis. Pin 1 jumpered to pin 3

And pin2 ( the green wire) is the "hot" signal...guess, unbalanced.... this could be a line input too then up to at least 10 or 15k? feeding a 200 ohm from my mixer output should be fine then...i ... hope...

[Paul JD]

Originally Posted by Paul JD

If pin 3 is grounded then it is unbalanced. Balanced connections have 2 phases, a non inverted signal and an inverted signal, when pin 3 is grounded the non inverted signal is grounded out so you are only left with the non inverted signal i.e. unbalanced.

Whoops that should read "the inverted signal is grounded out"

[Herald1360]

Originally Posted by Paul JD

It's common practice to refer to them as hot and cold, hot being the non inverted in phase signal and cold being the inverted out of phase signal. https://en.wikipedia.org/wiki/Balanced_audio

Thanks for that. It's just common usage rather than the actual state of affairs, then. Hot and cold would make more sense in the unbalanced situation.