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Author Topic: Looking for a compact phantom power adapter  (Read 3278 times)

Scott Carneval

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Looking for a compact phantom power adapter
« on: January 12, 2012, 12:42:28 am »

I just did an install using a DBX Zonepro for processing.  There is an A&H console for FOH, but they want a very simple solution for a single poduim mic without having to bring in an audio tech and fire up the console.  The Zone Pro has two free mic inputs, but it doesn't provide phantom.  They have a Shure MX412DC that of course requires phantom.  I want something compact that I can tuck into the back of the rack to provide phantom on that channel.  It must be AC powered, not battery.  Preferably hardwired via euroblock, but XLR will work too.  So far I'm finding ART, Behringer, and a few other brands I'm not familiar with.  The nicer units are all much bigger than I would like.  Any suggestions for a compact unit?
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Tom Young

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Re: Looking for a compact phantom power adapter
« Reply #1 on: January 12, 2012, 07:08:58 am »

I just did an install using a DBX Zonepro for processing.  There is an A&H console for FOH, but they want a very simple solution for a single poduim mic without having to bring in an audio tech and fire up the console.  The Zone Pro has two free mic inputs, but it doesn't provide phantom.  They have a Shure MX412DC that of course requires phantom.  I want something compact that I can tuck into the back of the rack to provide phantom on that channel.  It must be AC powered, not battery.  Preferably hardwired via euroblock, but XLR will work too.  So far I'm finding ART, Behringer, and a few other brands I'm not familiar with.  The nicer units are all much bigger than I would like.  Any suggestions for a compact unit?

Check out RDL (Radio Design Labs). Their FP-MPA2 will do what you need.

http://www.rdlnet.com/product.php?page=59

Or Crown's CS 5 PS 12

http://www.akg.com/site/products/powerslave,id,1167,pid,1167,nodeid,2,_language,EN.html

There are probably others
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Tom Young
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Scott Carneval

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Re: Looking for a compact phantom power adapter
« Reply #2 on: January 12, 2012, 11:31:37 am »

Thanks Tom.  I'll probably go with the RDL unit.  I came across a 'Stick On' adapter by RDL but that didn't really inspire much confidence. 
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Tom Young

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Re: Looking for a compact phantom power adapter
« Reply #3 on: January 12, 2012, 11:47:48 am »

Thanks Tom.  I'll probably go with the RDL unit.  I came across a 'Stick On' adapter by RDL but that didn't really inspire much confidence.

I agree they dont look terribly impressive. But audio performance and long-term reliability have shown to be very good. Cost is reasonable.
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Tom Young
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Kevin Maxwell

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Re: Looking for a compact phantom power adapter
« Reply #4 on: January 13, 2012, 12:06:04 am »

I just did an install using a DBX Zonepro for processing.  There is an A&H console for FOH, but they want a very simple solution for a single poduim mic without having to bring in an audio tech and fire up the console.  The Zone Pro has two free mic inputs, but it doesn't provide phantom.  They have a Shure MX412DC that of course requires phantom.  I want something compact that I can tuck into the back of the rack to provide phantom on that channel.  It must be AC powered, not battery.  Preferably hardwired via euroblock, but XLR will work too.  So far I'm finding ART, Behringer, and a few other brands I'm not familiar with.  The nicer units are all much bigger than I would like.  Any suggestions for a compact unit?
Which zone pro do you have? All of the ones I looked at have 15vdc phantom power. And the Shure MX412DC power requirements are 11 to 52vdc phantom power. So it is all built in and you should be all set.
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Scott Carneval

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Re: Looking for a compact phantom power adapter
« Reply #5 on: January 13, 2012, 11:23:38 am »

You're right Kevin, I didn't realize it had 15v.  What's funny is there's nothing in the manual or on the back of the unit about how to engage the phantom.  I just called my contact at DBX and he confirmed that it does in fact supply 15v whenever the mic/line switch is engaged to mic level.  I've probably installed 6 of these things in the past year and never realized.  Thanks!
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John Roberts {JR}

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Re: Looking for a compact phantom power adapter
« Reply #6 on: January 13, 2012, 11:46:20 am »

You're right Kevin, I didn't realize it had 15v.  What's funny is there's nothing in the manual or on the back of the unit about how to engage the phantom.  I just called my contact at DBX and he confirmed that it does in fact supply 15v whenever the mic/line switch is engaged to mic level.  I've probably installed 6 of these things in the past year and never realized.  Thanks!

That (low voltage phantom**) is pretty common in install boxes, and most people just plug up the mic and find that they work...  Most modestly priced mics will operate from the lower phantom voltage (often +12V to 20V), and you usually don't encounter silly studio mics that really need 48V in fixed install applications.

Many mics pad that phantom voltage down to well less than 10V for internal circuitry. If the mic output is tens of mV level, how much supply does it need? 

JR

** the lower voltage phantom while not designed to any firm official standard (AFAIK), the 6.8K build out resistors commonly seen with 48V phantom are dropped down as low as 1k ohm to supply adequate current from the lower voltage. 
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Geoff Doane

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Re: Looking for a compact phantom power adapter
« Reply #7 on: January 13, 2012, 03:17:16 pm »

That (low voltage phantom**) is pretty common in install boxes, and most people just plug up the mic and find that they work...  Most modestly priced mics will operate from the lower phantom voltage (often +12V to 20V), and you usually don't encounter silly studio mics that really need 48V in fixed install applications.


I was a bit reluctant to mention this, since it would probably void the warranty on the equipment, and should only be done by a competent tech, but it looks like the problem is already solved, so here's something to think about.

I've added phantom power to a number of devices over the years using a circuit based on this AKG schematic:

http://www.akg.com/mediendatenbank2/psfile/datei/79/b184a2f6c1ec90c6.pdf

The last time (on a really cheap BearRinger 1-channel mixer), the large blocking caps were already in each input lead, so all I needed to do was add R1 and R2.  Although it's not shown on this schematic, I believe AKG used 2.2KΩ resistors with an 18V supply.  With 15V, I dropped them down to 1.8KΩ and everything seems to work fine.  For best results, you should probably select two resistors that are as close as possible to the same value, to preserve the CMRR of the input.

PROS: very cheap and compact to implement

CONS: voids warranty, "modified" equipment can't be simply swapped out in case of failure, can't be easily turned off

GTD
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Re: Looking for a compact phantom power adapter
« Reply #7 on: January 13, 2012, 03:17:16 pm »


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