Jackfeilds and MicLevel/Phantom

[KeithGinty]

Hello

 

I have just designed a monitor and front of house system and have just found a made a bit of a mistake.

I was planning on using a Behringer PX2000 as my Splitter, but suddenly it hit my that they probable dont like phantom power.

 

The questions I would like to ask is the following.

A) Does PX2000 work ok with Mic Level signals.

B) If not could I use a Jackfeild

C) Where can I buy a 1/4" Jack Feild, 1u, 48 jacks, solder joint at rear (to allow splitting)

 

If I am talking rubbish how should I do to get this working.

[johndenim]

Can I ask why you need phantom power through a patch bay?

 

I understand you want this for live sound but you need to explain a bit more about your requirements.

Any patch bay will work at line level, I can't understand your config.

Please detail your set up.

 

John Denim.

[Bobbsy]

If you check the bottom of page 2/top of page 3 for the PX2000, it says pretty specifically that the unit should not be used for mic level signals and certainly not carry phantom power. Certainly phantom is a bad idea on any connector (like any variation on a TRS jack) where there can be momentary connections between "wrong" parts of the connector. The mode switching (normalled, half-normalled, etc.) on the Behringer box adds to the risk of using phantomSimilarly, it's bad practice to mix line and mic level signals in the same patchfield.

 

When designing facilities, I've always restricted standard audio patchfields to balanced line level devices and, where mic patching was needed, built rows of XLRs and short XLR patchleads for this purpose.

 

Bob

[p.k.roberts]

I've just had a quick squint at the specs for the PX2000 and the reason it won't pass phanton power is that it is unbalanced; there is no real electrical reason it wouldn't pass a mic level signal, but what it would do by unbalancing the signal is make the inputs much more prone to interferance and crosstalk.

 

I've worked in many studios which use 3 pole jacks for mic patching with no problems at all. You might want to have a look in the Canford catalogue; they stock some fairly reasonably priced Neutrik 'A' gauge jackfields.

[paulears]

I've done it too, but it isn't worth risking it if there is any chance of uncontrolled patching. I did this in my old college studios, to enable two mic boxes in two rooms to be patched to the main 32 input desk in the studio. Bad move! Apart from the terrible bangs when students patched while faders open and phantom applied. We had two identical desks, one with patching, one without. The patched version suffered numerous failures of input channels, I'm assuming that the 48V up the 'wrong spout' so to speak, was responsible for the failures as the other desk was fault free.

 

The mic level circuits also required very frequent cleaning to maintain noise free operation.

 

I'm still a bit confused about how you want to run the system - you mention splitting? Could you let us know how you want to use the prospective system?

[Bobbsy]

Sorry, but I still think it's bad practice to use any form of jack plug to carry phantom power. The tip and ring of the jack will both be carrying 48 volt phantom and, during insertion, can touch the jackfield chassis and then the "wrong" spring loaded contacts on the way in. Even if it works most of the time, it strikes me as asking for trouble.

 

Beyond that, if you have mic level (with phantom) and line level on the same jackfield format, the potential is there to accidentally send phantom into a line level source or accidentally mis-patch two phantom sources together. This is before considering any noise and crosstalk issues caused by running mic level adjacent to line level.

 

Maybe I'm just fussy but no studio setup I've designed has ever used standard jackfield for mic level.

 

Bob

[MarkPAman]

Behringer do make a balenced version, though for all the reasons Bob gave I would not use it for anything with phantom power going through it.

 

In fact the manual says:

 

Microphone inputs are for very low level signals and should never be routed via a patchbay. Plus the +48 Volt phantom power from the mic input could damage other equipment. It is best to plug mics directly into the mixer or via a wall box using good quality balanced multi-core cables.

[Bobbsy]

I'm still a bit confused about how you want to run the system - you mention splitting? Could you let us know how you want to use the prospective system?

 

We posted at virtually the same time but at least we agreed!

 

Regarding using the jackfield as a splitter, one of the modes you can switch to is to parallel all the terminals on one unit, allowing it to be used as a splitter. However, as it turns out to be unbalanced, I'd say it's pretty much useless in any professional application.

 

(As an aside, when planning audio patchbays I used to build in a few strips of paralleled jacks. These were often useful for things like comms etc.)

 

Bob