Bantam patchbay normalling question

[Martin]

Hi all

Wiring in some patchbays and wondering if there's a trick to making the ground wire also be normalled to the bottom row from the top row. I get continuity on all three conductors with a patch cord in there.

I assume the ground of the top and bottom row connected isn't a good idea as that means there will be grounds going all over the place [/i]

[rob]

oooo that is such a deep question you have asked

the "normal" practice is to link the ground from the top to bottom row.

Think of it this way. If there was no normalling and you patched from the top to bottom row you'd be connecting the grounds together anyway via the patch lead, thus using normalling to connect the top to bottom row you might as well maintain the ground connection.

If you are looking at ground lifting. Then the place to do this is at the equipment end of things.

Also if this patch bay section was connecting a stage box ( top row ) to mic preamps ( bottom row ) you'd need the grounds connected in order for correct shielding and phantom power return in order for the normaling to work at all.

Of course if it was a patch bay section for mic pres / stage / wall box, then you'd be wanting to fully normal the patchbay, not half normal it.

Rob

[Martin]

Heard from the horses mouth..

8 hours soldering today did about 60-70 bantam (read: small!) connections and its all going pretty well

used lead free solder which is a little harder to work with but seems to flow just as well once you get enough heat on it, smells different which is probably a good thing...

okay so grounds connected, at least that is easy enough to do

i suppose they are connected eventually anyway but the curious thing is the patchbay already had a few connections on it that i took off, and they only had the hot and cold (no ground, shield etc) connected, even though you aren't using A at the time


the reason i asked first was because of this for example

a: monitor output of main recording system on top row
b: main monitors directly below it (forget volume control for the minute)
c: second output of different recording system elsewhere on the patchbay

A is normalled to B, sheild wires connected as above, so are on unless you plug in C - and now the sheilds of A, B & C are all connected...

i thought it might result in a ground loop or something not very fun like that, although all the gear is connected through the same tech power circuit so it should hopefully be pretty clean

[Damien]

rob, why full normal not 1/2 for box to pre?

also what is the easiest (and the best, which usually isnt the easiest) way to have one mic to to 2 pres.

we have 1/2 normaled from input box to pre, so i can split at the patch bay to a second pre... and are careful with phantom..


also does anyone have a cct diagram for phantom power blockers. (2 xlr's with stuff inside) i want to put some inline with our ribbon mics to prevent "oops".. these can be removed once you have patched and settles, but we keep re patching at the patchbay coz its new and fun and its going to cost us soon, especially with so many new inexperienced friends dropping in to "help"

actually while in at it, does anyone have a cct for phantom power testers that generate pink/1k tone when power is present, and have leds to confirm what pins are working.....again in an xlr connector. i have a green and red led in an xlr, this works well, but no tone.....

[rob]

full normaling so you don't get the normalled mic pre ( on the bottom row ) left connected to the mic ( top row ) when you patch that mic across to another pre.

ie exactly to avoid what you are then asking in how to connect one mic to two preamps

so, as a starting point i'd always set up a patchbay so that you didn't "accidentally" get one mic connected to two preamps because in most situations you wouldn't want this.

However if you do want to connect one mic to two pres....and why not...there are no rules. Then a simple Y split can work. ( or your half normalled patchbay ). Often this will work ok....but it isn't perfect. You can get grounding issues between the pres ( plugging both into the same power board helps ) and importantly the loading of the mic is the combined input impedance of the two preamps. This isn't necessarily a bad thing and indeed with some mics ( older tube types....but not ribbon mics ) can be a good thing. But there is also a loading issue on the phantom circuit. With most preamps, turning the phantom on on one preamp and off on the other will result in the effective phantom voltage being reduced by half!

confused...i am

other than that and special tranformer mic splitter can be the go....but then you are introducing a transformer into the signal path....this can be good...or not so good

nothing is perfect and everything is interesting

or block the phantom from going up the arse of the second preamp and being reducted by half. Maybe this is the best solution.

Which is your next question.

so to block phantom you just need to be put two caps in the signal path. One in the hot leg and one in the cold. At least 100uF 50V would be the go and bipolar types are better ( oops an opinion about capacitors!!! erk ) and significantly you don't need to think about the polarisation and which way round to place them

whew

Rob

[Martin]

well i've got the odd buzz or too but overall my soldering was successful..

i'm thinking of perhaps not normalling the speaker inputs as they are going to be swapped from system to system quite often and don't particularly need to be into the one


i'm going to be posting here about ground loops and things very soon i think (once i get every bit of gear fired up)

[Damien]

our place. 100 % wired. not a single buzz hiss nuttin......

not a lead out of phase, wrong place....

there has to be a fault, but so far i cant find it....

wheres that wood again.....touched...i feel good..dun nah nah nah...just a lil bit mad dun nah nah nah