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Gear / Technical Help => Microphones & Setup => Topic started by: Breeze on August 18, 2011, 11:19:47 PM
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I've noticed that a lot of the new phantom powered AT mics run from 11 to 52 VDC. In principle that makes it simple to just wire 2 9-volt cells in series to make a battery box.
Does anyone know if there's a performance penalty on these mics for not running from 48v pp? Thanks.
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Generally no, if a mic states it will tolerate phantom power between 11-52v then that's what it takes to operate within it's sonic spec. Now it might have a higher current draw the lower the voltage is (Schoeps cmc6 being an example, it's P12 draw is 8ma compared to 4ma at P48), but sometimes it's not any different and you really gain a benefit running lower.
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Thanks!
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One note about constructing adhoc battery boxes, make sure to get the appropriate resistors (among other things) for the phantom power, but thats a whole different topic.
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The standards are 680Ω for 12V and 6.8KΩ for 48V. The standard that practically nobody ever used for 24V is 1.2KΩ. A 2x 9V battery box will be between 16V and 18V, so there is no standard but something around 1KΩ should do...
Thanks: that pdf was very enlightening. Odd how the resistor value seems to increase almost exponentially vs a linear voltage increase; by that, 1k seems about right for 16-20v. 0.4% matching is recommended but I usually try to match resistors in balanced circuits to .1% anyway. I also contacted AT and they replied that as long as you're within spec on the pp voltage, you can expect 100% performance. VERY convenient! :)
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here is a quick snip from the team Milab thread regarding this topic:
could you let us know what db level would qualify as "normal" I mean many (most) us are often using these mics a loud rock concerts...
would running at 16v phantom be any different than at 12v?
thanx
--Ian
Hi Ian,
I'll talk to Per Ove and see if we have any documentation or if we can make some new tests just for you.
Thanks,
Mattias
Mattais,
Thank you very much!
--Ian
Hi Ian,
Ok, so I just had a talk with Per Ove about this. I'm not an engineer and he explained this to me in Swedish, so forgive me if I get something wrong. Per Ove points out that the main reason why the max SPL is a little lower at 12V is because of technical issues with phantom power when running at low voltages. The "phantom resistance" at 12V should be only 680 ohms (6800 ohms at 48V) which limits the signal level of the microphone.
The easiest way to avoid this problem is to require 48V phantom power at all times - something many other manufacturers do.
/Mattias
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The correct answer is, "It depends on the microphone." Some microphones deliver every bit as good (or poor) performance at the low end of the voltage scale as at the high end. Others don't. There's no standard for phantom powering at "9-52 Volts" or "11-52 Volts" so people shouldn't expect any particular regularity or consistency in behavior among microphones that are designated in that way.
The IEC standard supports 12-Volt and 48-Volt phantom powering, and the current version also describes a 24-Volt method which never caught on and will probably be removed from the next version of the standard (due out fairly soon if I recall correctly).
--best regards
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This was Audio-Technica's reply. I asked about this as a general question about 11-52v condensers, but since I had to enter a model number, his answer specifies one mic:
There will be no appreciable difference/variation in performance between 11v to 52v of Phantom Power on the BP4025. The only time you should see variation in performance is if any given microphone requires 48v-52v, and you give it anything less/more than.
Therefore, the BP4025 will perform the same should you provide it with 11v-52v of Phantom Power.
Hope this helps!
Dan Pelletier
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If there's nothing lost running at lower voltages, it would be even better to run low because the batteries will last longer. My Littlebox has two voltage selections and I run low whenever possible for that reason.
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More confirmation from AT:
Any A.T. microphone rated 11v – 52v Phantom Power can handle any voltage within that range, and will operate at the same quality. Please keep in mind that some microphones will require the full 48v of Phantom Power for operation (such as the AT4050, which works at 48v). When reviewing the specifications for any of our microphones, you can trust the specification because of our strict Quality Control.
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Short heads up. It depends on the exact mic circuits. Schoeps CMC6 mentioned above will run without degradation at EITHER 12 or 48 Volts, but not arbitrary Voltages in between according to the manufacturer. This is one special case, and there probably are others.