SommerCable Passive Transformer Isolated Microphone Splitter

[neodyms]

Hi all !

I'am working as Sound Manager in a french room
Actually solving a problem with our 60 channels passive transformer isolated microphone splitter.

This spliter box contain 15 x  4 channels SommerCable Modules likes This :

Generally we use it like
Direct out for the Mnt Desk witch feed in Phantom Power
Iso  Out 1  for the Foh Desk
Iso Out 2 for the Brocasting or Reccord Desks

The problem is a hum sound and the poor quality passing thru this modules :

About the quality question :

SommerCable supply  this 4 channels modules with two options around the transformer
No Name SommerCable Or Lundhal 1570
With have the "no name" version ... of course // i hope to get the budget to buy individually 60 x  Lundhal 1570

Regarding the 2 two transformers tech spec they are big differences  :
Please see in link this two tech specs :
https://drive.google.com/open?id=0BwGGieYb0SNwM0c2Wk5FWnVVLTQ

About the Hum Sound question :

When i hear this sound, i think about  explorating  the ground wiring topic

I don't  have any problem between the input and the direct out  (logic isn't it ?)
All the wiring in input  and output is in common ground ... i can't change it
It's in harting connectors 20 pairs with common global ground like this :

This is  the schematic simplified  by only one channel of the module :

What is exactly the goal of all this caps and resistors ?
What about the grounding  management ?

After reading some splitter literature i'm a bit perplex about this schematic
Please read in link this  3 documents :
https://drive.google.com/folderview?id=0BwGGieYb0SNwaFJpNzVTTFctSWM&usp=sharing

What about the Step-down mode ?

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Can i do this ?  :

 

[Gene Pink]

On your schematic with the two transformer primaries in parallel, the lower one is out of polarity. A mistake in drawing?

Gene

 

[radardoug]

As Gene Pink says, the paralleled primary is out of phase. This would not work. The basic circuit looks fine, all the parts have a purpose. The iso grounds are separated from the direct ground by capacitors. This will tie it all together at rf. The secondaries have zobel networks, presumably calculated, and series 100 ohms for isolation.

 

[neodyms]

i just verified the pcb wiring and yes it's really like this.
you're right they don't respect the dot convention below

 

[aomahana]

The circuit looks fine.

I would suggest you buy 1 or 2 of the Lundhal 1570 and see if this eliminates the hum. As well as better frequency specs, the Lundahl  may have better shielding.

On a side note, around the year 2000, pin 3 Hot was changed to pin 2 Hot. Pin 1 remained at ground.
It is worth checking all your attached equipment is configured with this convention.

 

[neodyms]

On a side note, around the year 2000, pin 3 Hot was changed to pin 2 Hot. Pin 1 remained at ground.
It is worth checking all your attached equipment is configured with this convention.

yes sure ! MNT and FOH mixing desk are usually Soundcraft VI6 and all the broadcast equipment is generally  brand new.
so i can exclude this hypothesis

 

[neodyms]

OK

I restart at the beginning.
I contacted OEP transformer to see what product they can propose me
they send me this datasheet (see attached file)... pretty good !

So based on the jensen publications  about this topic,  I've done this following schematic :

What do you think about it ?

 

[neodyms]

in input i have 20 channels with common ground wiring
in output to

so i will have 20 RF network (51 ohm + 10 nF) in  parallel ! maybe a weird equivalent network ?
would not it be more logic to put nothing ? or just a switch ? 

Second Question :

How can i protect the transformer from 48v DC voltage of the Phantom power ?

 

[[silent:arts]]

How can i protect the transformer from 48v DC voltage of the Phantom power ?

You don't need to protect the transformer from Phantom Power.

 

[nielsk]

I have used , wired, and installed many large splitter systems, never found any of the " cap & resistor" or "tie to transformer shields" on the iso grounds of any use.
Make the ground lift switch an actual ground lift switch. Eliminate the cap and resistor  so pin 1 is totally dis-connected when the switch is lifted. Shield will be still connected at the other end of the cable, and actually be a proper telescoping shield.
This ground gobbeldy-gook is probably where your hum is coming from. If there are currents in the shields of the iso outs and they are connected to the transformer inner shields the noise will couple into the signal.
Shield ground should connect input to direct output and transformer shield only. I never even bother with  lift switches anymore as it is always "up".
Results trump theory every time....