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9V power distribution box


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Here's my latest project:  a 9v power distribution box.

Many factors led me to make this custom distro unit.

1) I use Audio Ltd and Micron radio mics, both of which want 9v external power.  Microns say they'll take 7.5-16v ext power, but they say ALWAYS use their custom cable, which has a 9v regulator built in.  And Audio Ltd specs say they'll handle 9-14v DC, but NP Li-Ion batteries at full charge will put out 16v.  I don't have the luxury of the 10-18V range of Lectro's.

2) Of the off-the-shelf solutions, only Hawk-Woods has a 9v-regulated distro box.  The BDS, from what I can tell, passes along whatever voltage it receives.

3) My Microns don't have a pilot tone to mute the receiver output when no Tx is present.  So intermittent bursts of RF can hit the receiver with so much energy that, even with the pot down on that channel, it nails the front end of the preamp, and taps the power rails on my Cooper CS-104 mixer, which can be heard on the other channels being used.

4) Both Audio Ltd and Micron have inconvenient methods of powering on/off.  The most intuitive way is to plug in the connector, and voila, power on.  (The Audio's do have a tiny switch, but it is generally buried when in a bag rig).  I don't like the idea of pulling the Lemo connector each time I wanted to power down unused receivers.  It will tend to shorten the life of the connector, and put additional strain on the wiring to the connector.

With all that in mind, here's the current progress on my switchable 9V regulated distro box.

NP power comes in thru 4-pin XLR-M.

Splits to (2) 5A PTC fuses.

Output of 1 fuse goes directly to 4-pin XLR-F to feed 788T.

Output of 2nd fuse goes from the breadboard to feed each DPDT switch.

Each switch, when engaged, feeds the 9V regulator.

9V regulator goes back to each switch.

Each switch feeds an LED and an individual output.

The regulator only turns on when a switch is engaged.

Outputs are (4) Hirose HR10-7p-4p (like on SD recorders); and (2) DC connectors.

I'll post the final as I finish up.  Nearly done.








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would love to see a line drawing of this.. 

I was on the war path to making one of these as well (though much simpler.. no regulator or switches aside for a single master) but ran out of time before a gig and ended up buying a battery bud.  A nice box but not enough outputs generally (I see they have a new version out with 5 outputs)

I understand the desire to keep it small if it's meant to power a bag rig..  not a lot of free real estate usually.

I'm curious why you decided to go with a linear regulator over a more efficient switching regulator?  Because of noise concerns?  Did you put a master switch before the regulator to avoid slowly draining the battery?  (not sure how much of a factor that is.. but linear regulators drop the voltage by burning it off in the form of heat?  So wouldn't this represent a constant battery drain if connected?)

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Mostly finished this up.  I had to have it field ready for a gig starting yesterday.  So far so good, but it's a simple gig... boom and one radio.  Will patch in the last DC connector and give it more thorough testing next week.

Phil- Thanks.  As for the size, I wanted to keep it small enough to fit in a bag.  I started, of course, by looking at off-the-shelf products and didn't want to go too much bigger from there.  After going under the hood on my Sonosax a couple times, this was like working on an old American car... like when there's so much room, the mechanic actually sits inside the engine compartment.

On the cart, this will just support the Microns.  The 788T and the Audio's (in a quad box) will run from a Powermax.


As Vin said, PTC fuses are widely available from several manufacturers.  I used NTE because they were available from my local electronics shop (the excellent Al Lasher's in Berkeley).

I didn't actually consider a switching regulator.  The T-220 form factor was easy to work with; the LM2940-CT had been suggested by Evan at Vark Audio as a good one to use for the Audio's.  The regulator is screwed to the chassis of the box, so that helps dissipate heat through the surface of the box (you won't see that in the photos below... hadn't done it yet).

No master switch before the regulator.  It's wired so that no power gets to the regulator unless I turn any one switch on.

I'll see if I have some of my drawings around.

Yes, the gauge was a bit overkill, but once I started, I didn't want to work backwards.  I put about three strands inside the Hirose's and put the others on the outer edge.  Then covered both in heatshrink tubing.

Here's a few pics of the (mostly) finished box...

You may notice red switches where the previous were blue.  The blue ones sucked and melted, even at moderate solder temps.  Life got easier with a switch that was only 50 cents more.





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  • 5 weeks later...

  Hey dude can you make me a 4-pin XLR cable that goes from 12-volt M and ends up 9-volt F?  I would love that for my new UHF tuner box!  ha ha

  But seriously, that is amazing that box you made, it looks super pro with the lights and switches.  Can you tell I have no clue how to do this shit?  Man I need to take some electronics course somewhere...

  Dan Izen

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  Hey dude can you make me a 4-pin XLR cable that goes from 12-volt M and ends up 9-volt F?  I would love that for my new UHF tuner box!  ha ha

  But seriously, that is amazing that box you made, it looks super pro with the lights and switches.  Can you tell I have no clue how to do this shit?  Man I need to take some electronics course somewhere...

  Dan Izen


I posted this on another thread too, but the Powermax can output 9v.  Pin 2 is adjustable from 5v-9v.

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Just checked on this thread after awhile away...

@ Chas

Thanks for the prompt...

It works like a charm.  No problems.  On/Offs all work appropriately, and when all switches are off, the regulator stops receiving input voltage.

@ Dan

If you're a "class" learner, that's probably a good way to get an intro to electronics.  I never did that.  I started by taking apart my X-wing fighter when I was a kid to see how the little light turned on when you pushed the button.  Fast forward 20+ years... I still do the same thing, except with gear worth a helluva lot more.  I've gotten advice from people who are electronic wizards.  And learned everything else online.  Just this year, I finally memorized the equation for watts = amps x volts.

You don't have to know this stuff to record good production sound, but it can save a few bucks in cables and gear maintenance.

PS - I do this tedious work so much for myself, I'll politely excuse myself from making your 12v-9v cable :)

@ millard52

I'm not sure I understand your question... "can we use some switches to make it more feasible?"



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