Plugs on Phantom power cords

[ksor]

I'm planing this new front panel with two of Bo's DI-Boxes included - see the attached file for layout - the 2 X 3 jacks to the right of the panel.

I'm new to this HD-recording, balanced cables and Phantom Power cords !

I know I have to be carefull about grounding and insoletion from chassis but as you can see I plan to let the XLR OUTPUT be replaced by a 6,5mm female stereo Jack, BUT ...

then the Phantom Power FROM mu Phase88 TO the DI-Box is exposed in the MALE 6,5mm stereo jack ... is that allowed ?

There should be no harm IF I connect "backwards" but ... what if connection is done the other way around ... will there be a momentary shortcut when the plug in inserted ?

I would NEVER do this kind of configuration with a 240V power cord ... a MALE plug in each end ... never - maybe the same precaution should be taken when talking Phantom Power - please guide me !

 

[ruffrecords]

Don't know whether it is allowed or not but it should be OK. If phantom power is shorted all that happens if  that 3K4 gets connected across 48V and hence draws 14mA which is just over 300mW in each 6K8 resistor. Any decent phantom supply should cope with this.

Cheers

Ian

 

[ksor]

Instead of "allowed" maybe I should ask "is it good practice ?"

 

[JohnRoberts]

It is not generally dangerous wrt power since it is only modest 'average' current due to series build resistors, but a potential issue from shorting a charged phantom power DC blocking capacitor is that short can transiently dump amps of peak current into preamp input devices when the top of a cap charged to 48V gets pegged to 0V driving the low side to -48V.

"Good practice" is to clamp and protect these input stages, but an exposed male connector does increase the possibility of inadvertent shorts to ground, so I certainly would make sure to use adequate clamping in such a scenario.

JR

 

[MagnetoSound]

I'm curious, what reason do you have to not use XLRs?  :-\

 

[ksor]

I'm curious, what reason do you have to not use XLRs?  :-\

Look at my design ... I don't think an XLR will do any good there !

Then

1) price ... I have FEMALE stereo Jacks on the shelf !
2) most often the ballanced output from the DI-Box should be plugged into jack 7 OR 8, witch are FEMALE stereo 6,5mm Jacks
3) the short cables are much cheaper with two stereo Jacks than cables with XLRs

(What is such a FEMALE "thing" you can plug into on the rack called in english ?    .... Google translates the danish term to "bush" .... I don't think that's the right word, even though some nutcase should plugged something into him long ago  :-\ !)

 

[ruffrecords]

(What is such a FEMALE "thing" you can plug into on the rack called in english ?    .... Google translates the danish term to "bush" .... I don't think that's the right word, even though some nutcase should plugged something into him long ago  :-\ !)

Socket?

Cheers

Ian

 

[ruffrecords]

It is not generally dangerous wrt power since it is only modest 'average' current due to series build resistors, but a potential issue from shorting a charged phantom power DC blocking capacitor is that short can transiently dump amps of peak current into preamp input devices when the top of a cap charged to 48V gets pegged to 0V driving the low side to -48V.

Good point which I always forget because I only use transformer mic inputs.

Cheers

Ian

 

[ricardo]

It is not generally dangerous wrt power since it is only modest 'average' current due to series build resistors, but a potential issue from shorting a charged phantom power DC blocking capacitor is that short can transiently dump amps of peak current into preamp input devices when the top of a cap charged to 48V gets pegged to 0V driving the low side to -48V.

"Good practice" is to clamp and protect these input stages, but an exposed male connector does increase the possibility of inadvertent shorts to ground, so I certainly would make sure to use adequate clamping in such a scenario.

Inputs using SSM2017/9, 1na217 and their recommended circuits are flaky.  Use the THAT 1510/2 circuits and their protection (high current diode bridge to the rails) even if you use SSM & 1na.

There is also a danger of damage to condensor mikes.  Shorting one or two leads can zener the output transistors on a Schoeps type circuit.  The mike still works but is suddenly much noisier.  The measures required to protect the output transistors are rather subtle. eg

The common (exact original) "Alice" circuit with minimum protection is OK as is the full Dip. Ing Wuttke Schoeps circuit.  Some "improvements" to Alice (which do improve certain parameters) open the output transistors to this type of failure and require all the mod cons that Dip. Ing. Wuttke uses.

I don't think it's good practice but even Calrec/BBC broadcast desks used jacks in their patch panels though we tried not to have P48V anywhere near them.

 

[ksor]

Now I'll focus on what started the thread - my changing the OUTPUT XLR to a 6,5mm stereo Jack socket.

It's my private home hobby studio so I think I'll just connect "backwards" (from the DI-box to the input WITH Phantom Power) then surely nothing happens.

All my condenser mikes have XLRs - so no danger there.