B-gauge jacks

[sandall]

When making adaptors from PO (B-gauge) jacks to other things I've always assumed tip = hot, just like A-gauge (tip is tip, innit?), but somebody has just come up with the theory that tip is actually cold, so you don't get a bang when the loose end of a double-ender touches metalwork. It's now got me wondering. Any ex-wiremen out there?

[GaryNattrass]

Tip has always been hot to me for the past 38 years in broadcast using PO or B gauge jacks.

 

http://www.muzines.c...ect_1_large.jpg

[Brian]

As far as audio goes the tip is the 'hot' signal and has been from day one.

 

 

However, I *think* your confusion might come from the world of telephones. IIRC the central 48V DC supply is arranged so the +ve is connected to earth so that the DC on the phone line is -ve wrt to earth. The tip of the jack then had the more positve DC voltage on it, the ring the more negative. This meant that the tip was, back at the exchange, connected to earth.

[alistermorton]

Asking as a non-audio guy, can anyone explain where and why A and B gauge jacks are used, or is it just another historical artefact?

[sandall]

Thanks for the confirmation. The "is tip cold?" query came from someone with a comms background, so Brian's suggestion sounds logical.

 

Re Alistair's query - I believe (but quite prepared to be shot down) that the standard (A-gauge) jack came from the USA, while what we now call B-gauge came from the GPO, who had HUGE jackfields for distribution. When the BBC started they merely adopted the existing standard, followed by the rest of the broadcast & studio world. Another hangover from the GPO is that jackfield rows should always be counted from the bottom.

 

Sorry, Alister's query.....

 

 

[alistermorton]

Thanks - that makes sense. I guess That broadcasters might have used GPO tie-lines and so using GPO plugs to connect their equipment would be necessary.

[GaryNattrass]

We still have GPO B jackbays in our older studios at SKY, we had them at Teddington and Tyne Tees too but in the 90's bantams became the fave.

 

Now it is all Ghielmetti at SKY studios in Osterley http://www.ghielmetti.ch

[sandall]

Up to the time Television Centre closed most technical areas (even new ones) still used jackfields, which have the enormous advantage that anything can be plugged to anything (they also have the great disadvantage that anything can be plugged to anything, so a clear head is needed when "plugging up").

 

It also meant that there were an awful lot of places between source & listener where a line could be "lost", & it could be quite hard to find the "culprit" - most people who worked with jackfields will have tales of getting away with causing actual or near disasters with a misplaced jack.

 

Treat Gary's linked diagram with caution - it comes from a mysterious land where Tip = Right channel, unlike the rest of the known world where Tip = Left.

[sunray]

I've done my time on GPO switchboards and can confirm tip is +ve (Earth) & ring is -ve (-50v Battery [or +ve earth]). Of course in a balanced system there is no such thing as 'hot' & 'cold' as they are equal potential and opposite polarity but the tip is always +ve whether it's balanced or unbalance and as far as I'm concerned always has been, regardless of type of plug [A, B, 3.5, bantam, 3/8", etc). Interestingly I have always been under the impression that the A gauge plug originated as a 2 pole (tip and sleeve) with the red wire going to the tip and when stereo arrived the sleeve connexion was moved further from the tip to allow the ring to be added. The convention of red to tip remained and red = right became the norm, making the tip right. I have a plastic crate full with headphones, mostly Sennheiser/Canford and I reckon there is a 50/50 split, even within the same manufacturer. When I was building racks with patchfields (B gauge), on the rare occasions there was any stereo circuits on a single jack we retained the red = right = tip convention.

Edit: If any of the above is incorrect, I'm happy to be shown I have it wrong.

[GaryNattrass]

Treat Gary's linked diagram with caution - it comes from a mysterious land where Tip = Right channel, unlike the rest of the known world where Tip = Left.

 

Ha ha probably a sennheiser diagram as they seem to get things the wrong way round for headphones! http://www.blue-room.org.uk/public/style_emoticons/default/tongue.gif

[Richard P-W]

When I was building racks with patchfields (B gauge), on the rare occasions there was any stereo circuits on a single jack we retained the red = right = tip convention.

 

Just to add to the fun, I've been in facilities where the port/starboard convention is used for channel identification so left is red and green is right!

 

I was told that it began in the BBC and I have certainly seen PPM meters with red and green needles.

[sandall]

Just to add to the fun, I've been in facilities where the port/starboard convention is used for channel identification so left is red and green is right!

I was told that it began in the BBC and I have certainly seen PPM meters with red and green needles.

Not sure if it began at the Beeb, but it only tells half the story, so usually combined with another twin PPM with white & yellow needles for sum & difference.

[sunray]

Yes red & green on PPM's and their associated switchery. I have an ex BBC stereo PPM in a metal box which has 'A' (green needle)& 'B' (red needle)inputs, having not had that much involvement with such devices, I tend to use it as left = 'A' (green)and right = 'B' (red). I also have an ex TVS 2U unit containing a small, 4 I/p, audio switcher and 2 PPM's where o/p 'A' is 'left' meter etc. When I use the 2 units in the same system green is automatically left. I can't remember what convention my ex BBC Glensound mixer used.

[Bobbsy]

Thanks for the confirmation. The "is tip cold?" query came from someone with a comms background, so Brian's suggestion sounds logical.

 

Re Alistair's query - I believe (but quite prepared to be shot down) that the standard (A-gauge) jack came from the USA, while what we now call B-gauge came from the GPO, who had HUGE jackfields for distribution. When the BBC started they merely adopted the existing standard, followed by the rest of the broadcast & studio world. Another hangover from the GPO is that jackfield rows should always be counted from the bottom.

 

Sorry, Alister's query.....

 

My first broadcast jobs (1971-76) were in Canada and the three places I was familiar with there all used B gauge for jackfields. I'm pretty sure this stemmed from the phone companies there also using B gauge.