8128 insertion points unbalanced? Ground only on ring?

Ok so i'm ripping apart this neve 8128 patchbay ( the desk is only useful as channels with outputs via the insertion points.

EVERYTHING aside from the insertion points is on multicore looms, yay nice and easy to rewire into new patchbays. Insertion points, stupid ribbon connectors, so of course i have to manually get out the tester and find out what bit does what.

Now i'm assuming that its all unbalanced, but when i'm testing just using a patch lead plugged into the patch point and then measuring impedence on the pins, i can get ground on the ring, but i can't get ground on the sleeve... This may be a futile question and the answer is just bridge ring and sleeve on the new patchbay, but i thought i'd check if anyone knew if it held any specific reason for doing this.

If not, oh well, just bridge the two pins and have an unbalanced section of my patchbay (it normals into the -10dbu inputs on my PT rig anyway)

never used a 8108

might check with geoff tanor  at aurora audio www.auroraaudio.net/


If it's like other consoles the inserts are unbalanced, they share common ground. think trs to duel ts ala mackie and the like.

TheGuitarist said:

Now i'm assuming that its all unbalanced,

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Neve stuff is all balanced.

Ian

Then how could the ring on the patch be ground? Both the lead and patch point work fine.

Do you have the console docs?  You should document everything very carefully before you start ripping things apart.  I am not familiar with the 81 series, but the 80 series has loading resistors on the bay of different values for different circuits.  Make a complete map before you start the new bays and make them exactly the same as the old bays.  Who are we to presume that we know better than the Neve engineers, especially when it comes to the patchbay?  Of course "the times", equipment, and signal flow have changed, but the way to normal their comezouttas and guzintas internal to the console has not. 
Follow the ribbon back to the motherboard if you do not have the docs and determine what they did.  Beep-out an insert send and return from module to bay back to module.  Standard for a 80 series insert is balanced, half-normalled, sleeves vertically strapped and connected both sides to the frame back at the module connector.  I would expect something similar with the ribboned 8128.

This is not an "oh well, I'll do something else" moment.
Mike

TheGuitarist said:

Then how could the ring on the patch be ground? Both the lead and patch point work fine.

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You are going to have to be a lot more specific. Is this patch bay now completely disconnected from the console? What are you calling ground? Exactly how do you have things connected when you make these measurements?

The 8128 is from the 70s and was definitely all balanced. If it isn't it can only be because someone modified it.

Cheers

Ian

While connected to the console, the ring on the patch lead, connected to the output of an insertion point, connects to the console ground, i tested a loose grounding wire and impedence went to zero. Well around 1 ohm or something but you know.

The way i did it was, plug a patch lead into a patch point, i then tested continuity between the tip of the patch lead and started probing the pins on the connectors where they were soldered to the board until i got continuity.


Actually, there aren't even enough pins or connection points for it to be be balanced at all. For the middle section of the bay there are 3 10 pin connectors for 24 channels with each connector having two pins for ground. so there are 3 for outputs and 3 for inputs.

TheGuitarist said:

Actually, there aren't even enough pins or connection points for it to be be balanced at all. For the middle section of the bay there are 3 10 pin connectors for 24 channels with each connector having two pins for ground. so there are 3 for outputs and 3 for inputs.

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OK. Let's start with the basics. What is the model number of the channel amps whose inserts you are measuring?

Cheers

Ian

I stand corrected. However I still suggest talking to geoff tannor he will know for sure