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Old 3rd June 2006, 02:02 PM   #1
diyAudio Member
 
Join Date: Mar 2006
Location: Seattle
Default reducing phantom power

Asked in another thread, but got no love, so I am trying my own thread

if I build a mic from the panasonic capsule... it needs 2-10v of phantom power. If I buy a preamp, like the the Behringer UB802... they give 48v.

So... do I just hook up a resistor? Digi-key specs say the capsules use 0.5mA max... so... 82k ohms * .0005 amps = 41 volt drop... which would bring 48v to 7v (somewhere in the middle of 2-10v)

good plan? bad plan?
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Old 3rd June 2006, 03:20 PM   #2
moamps is offline moamps  Croatia
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Join Date: Oct 2002
Location: Croatia
Hi,

you might check out the schematics at

http://www.epanorama.net/circuits/mi..._powering.html

Regards,
Milan
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Old 3rd June 2006, 08:34 PM   #3
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Join Date: Mar 2006
Location: Seattle
Great link, thanks moamps.

Man, why are things never easy?

I (and independantly, owdi) want to take speaker measurements... so there is a discussion about mic's and mic preamps ... and buying vs Diy, etc.

Main recommendation was Behringer ECM8000 mic + plus a Behringer pre-amp (say UB1202 or UB802).

I am a bit grumpy about $130 (ECM800 + UB1202 ), but agree that building a pre-amp is likely not worth it, when you can buy the 802 for $50.

So, I think $50 for pre-amp, and I build a mic from the Panasonic Electret Capsule for more like $15... and I can live with $65 total.

Then this mess w/ the mixed phantom power...
Basically, the website moamps references says "good freakin luck using just a resister, try this..."
Code:
                           10u
    +---------o-------------||------o-----------------  HOT    (2)
    |         |                     |
    |         |-                    |
    |      CAPSULE                 22k
    |         |+                    |
    |         |            10u      |
    |         o-------------||------|------o----------  COLD   (3)
   2k2        |                     |      |
    |        2k2                    |     22k
    |         |                     |      |
    |         o--330R---o----o------o------+
    |        +|        +|    |+
    |        10u       12V  10u
    |        -|        -|    |-
  --o---------o---------o----o------------------------  GROUND (1)

The component "12V" is a 12 Volt zener diode
(don't ask me what's w/ the extra new lines... [code ] tags are weird.)

There is some other version of the circuit there as well.

I suppose that is not too bad. Too my rather limited knowledge at least the components are cheap.

However, here is my question (other than the implied question of 'am I doing anything stupid?') ... what if I just skip phantom power altogether. I use a 9v battery (if even that much) to power the capsule and call it a day (still using a decent Behringer pre-amp, just not using a phantom powered input)

Any big reason to prefer one way vs the other (other than batteries running out, I guess...)
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Old 5th June 2006, 03:31 PM   #4
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Join Date: Mar 2006
Location: Seattle
I am still curious how people who built mic's out of panasonic electret capsules are giving them the 2-10v power.

Did you:
  • build your own pre-amp (I sorta suspect this is most common)
  • build a circuit to reduce 48v to 2-10v?
  • add a 9v battery to your mic, and run without phantom power?
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