Building Phantom power unit.

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fromy

Member
Joined
May 22, 2005
Messages
13
Location
Norway
I`m using a sony DMX-R100 digital console and is feedup with only having phantom power at the first 12 mic inputs.

I`m planing to make an phantom powering box for the next 12 inputs (13-24).

Does anyone know how much current the phantom cirquit of the G9 is capable of delivering?

I guess it needs about 12 x 5 mA of current for my design, or is that not enough?

Schemo for the input at the DMX-R100

InputDMX-R100.jpg


The schemo says that there`s Jack input at 13-24. It`s one of neutrix combi xlr/jack, but I`m only using XLR

Do I need to stop the 48v DC before entering the mixer?


-- Fromy --
 
If you are going to make a phantom power supply imo you had best assume the worst case of when each line is shorted to common, hence pulls 48V/6.8k = ~7.1mA. Of course no mic will need this per se, but might as well have something that is robust against accidents and fault conditions (cable shorts etc.).
 
> worst case of when each line is shorted to common, hence pulls 48V/6.8k = ~7.1mA.

Note that this is per "line"; a shorted-to-ground mike (grounded center-tap, found in some old RCAs) can draw 14mA. However the current P48 spec says you need only supply 10mA per input. Not sure how to resolve this, and it is rarely a problem.

The conservative assumption is to scale the power for 12*14mA= 168mA, and let the shorted mikes smoke. The literal interpretation might call for 10mA current limiter on each input; nobody does that.

No, I don't recall how much the G9 supply is good for, but if it is one or two channels it is probably not enough for 12 inputs with worst-case mikes. (Many mikes cling to the older 2mA spec, but a few do hog nearly 10mA.)

Yes, you need to stop the 48V from getting into most mixer inputs. It would be good to have a parts-level schematic; there are several ways the inputs could be configured and you need different ways to block the DC. If you can peer inside, you may find that ch1-12 can be an example for ch13-24.

> feedup with only having phantom power at the first 12 mic inputs.

That's pretty cheezy for a $18K box; what's worse, this isn't documented in their website.
 
That's pretty cheezy for a $18K box; what's worse, this isn't documented in their website.

I know. It does have some disadvantages, but it sounds good and it`s compact.

Just compared the onboard micpre with my new built
G9, and the difference was next to nothing.
:shock:


-- FROMY --
 
I bougth this small powersupply (230 VAC - 48 VDC / 350 mA)

But I can`t imagine it`s rippel free. (It`s meant for LED lightening)

would a 100uF/63V el.lyt cap be sufficient to smooth things out?


-- FROMY --
 
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