Old 07-25-2013, 07:16 PM   #1
edkilp
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Default Phantom Power and mA Rating

Hi everyone. I'm close to purchasing a CAD M179 large condenser microphone. I want to use it as an all-purpose mic for my humble little home studio, all-purpose meaning mainly acoustic guitar and vocals. I really don't have the funds to buy a locker full of high dollar mics. From what I've researched online, this mic seems like it will do what I need it to do, given the variable pattern control and whatnot. My concern is the power requirements. I read a few reviews that claim this mic needs every bit of 48v as well as 8mA to operate properly. I use a Line6 UX2 as my audio interface, and I also have a Peavey PV10-USB mixer. The USB part is irrelevant in this case as I never use it. The UX2 puts out a nice 48.1 volts of power, but the mA is measuring at a meager 3.5. The mixer only measures 44.3 volts, and 6.53mA. Does anyone see this as a potential deal breaker for me? Neither device gets close to 8mA. I'm sure the mic will work, but will I be getting the full potential with these sub-par power ratings? Thanks.

Edward
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Old 07-25-2013, 07:26 PM   #2
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It will still work, but you will probably find that transient response will be affected. I have a matched triplet of Earthworks SR25 condensers and they are quite power hungry, the first interface I used them with (Alesis IO26) couldn't cope with all three connected at once, and when recording drums this was quite easy to hear as a sort of smeared distortion in the transients. Is it possible for you to try one out so you can test for yourself?
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Old 07-25-2013, 08:35 PM   #3
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Short of ordering it and returning it if it isn't satisfactory, there's no way for me to try before I buy. Which is the more contributing factor? The voltage or the mA as far as the transient distortion you mentioned? As far as mA, the UX2 isn't even close, but the voltage is good. The mixer will give me a higher mA output, but the power is about 3.5 volts shy of 48. Kind of a dilemma here, I think.

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Old 07-25-2013, 08:40 PM   #4
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You can also turn off the phantom power from your interface and insert an in-line phantom power box. Some of these are line/wallwart powered and some are battery. Rolls and Behringer and others make these things AFAIK.

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Old 07-25-2013, 08:58 PM   #5
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Originally Posted by Kihoalu View Post
.

You can also turn off the phantom power from your interface and insert an in-line phantom power box. Some of these are line/wallwart powered and some are battery. Rolls and Behringer and others make these things AFAIK.

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I looked at a few of those. I'd like to avoid buying yet another piece of equipment, even though these devices are relatively inexpensive. Especially considering that I have two devices here that provide phantom power. I never see mA listed in spec sheets. It is certainly not listed in the UX2 or the PV10 spec sheets. The PV10 manual, however, does say this:

If phantom power is used, do not connect unbalanced dynamic microphones or other devices to the XLR inputs.

I've read dozens of forum posts on the net that say this is not a problem for most dynamic mics. Now I'm wondering if I have to use either all powered mics, or all dynamic mics. I've definitely used both at the same time, and my dynamic mic is just fine. Maybe I'm fretting over that one too much. I'm seeing rave reviews for this CAD mic, and for my purposes, it seems like a good buy, but if the power issue is going to give me a distorted, smeared, low-quality sound, I need to re-think my strategy.

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Old 07-25-2013, 09:15 PM   #6
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From the M179 spec sheet:

Powering: Minimum Requirements are 24, 48 Volt Phantom Power capable of delivering at least 8 mA

This is beginning to confuse me a bit. If the minimum is 24 volts, I'm fine, but that 8mA thing is what concerns me. Does anyone have a dedicated phantom power supply who can measure the mA output? If I end up buying one of these units, I'll get one that can power at least 2 mics at once. Thanks

Edward
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Old 07-25-2013, 10:59 PM   #7
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Power supplies don't "push" current. A power supply puts-out a (hopefully) constant voltage. The current depends on the load resistance/impedance. (This unrelated to the microphone's impedance spec when the mic is putting-out the signal.) The relationship between voltage, resistance, and current is described by Ohm's Law


The current depends on the microphone characteristics, not the power supply. (It doesn't quite make sense that the mic is drawing 6mA from a 44V supply.)

If the power supply cannot supply the required current (say 8mA) then the voltage will drop. The fact that you are getting 48V indicates that the power supply is working correctly and supplying all of the current the mic "wants".

Typically, the mic's current rating would be the maximum/worst case, and the power supply rating would be a minimum... So an 8mA power supply will always work with an 8mA mic... The mic might require slightly less current, and the power supply is probably capable of slightly more.
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Old 07-25-2013, 11:07 PM   #8
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So, based on what I provided earlier, a mixer that measures 44.3 volts, and 6.53 mA, would you say that a mic that requires 24-48 volts and 8mA would be a safe purchase? Or should I consider a different mic? Or perhaps a dedicated phantom power supply? And what about the audio interface, that provides 48.1 volts, but only 3.5 mA? Thanks

Edward
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Old 07-25-2013, 11:58 PM   #9
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I've never seen anyone ever consider the power requirements of microphones (other than designers). I've seen endless obsession over opamps, cables, impedance but never phantom power. That's a new one for me.

More important things to worry about dude
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Old 07-26-2013, 12:05 AM   #10
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I've never seen anyone ever consider the power requirements of microphones (other than designers). I've seen endless obsession over opamps, cables, impedance but never phantom power. That's a new one for me.

More important things to worry about dude
What's so weird about it? If a mic spec sheet lists particular power requirements, and the power from my mixer falls short, why is that not a reason for concern? If you know anything about this mic, you'll see that for some reason, it draws a lot more than almost any of the high dollar mics. I don't know why, but it does. I just want to make sure I don't buy the thing, just to have it distort and sound bad from being underpowered. I believe it can happen.

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Old 07-26-2013, 12:34 AM   #11
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The CAD M179 is a good mic for the price, but it has a massive drawback and that is the power consumption, which is TEN TIMES that of the U87.

Given the many problems that such a massive current draw could give you, I would be reluctant to buy, not just becayuse of having sufficient power from the desk, but also the problems that a longer cable run can cause when more than usual power is required.

As it is just a Chinese budget mic and there are so many others, I would (if I were you) search for a good Chinese tube mic that has its own PSU and is models on the Neumann M149, or a better budget mic.

I got to try out the Violet Black Knight, which was very good -

http://www.soundonsound.com/sos/aug0...lackknight.htm

Also there is the Se-X1 and the AT2020 which both sound better than the low prices would suggest.

http://www.soundonsound.com/sos/feb0...les/at2020.htm
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Old 07-26-2013, 01:44 AM   #12
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Quote:
Originally Posted by EpicSounds View Post
I've never seen anyone ever consider the power requirements of microphones (other than designers). I've seen endless obsession over opamps, cables, impedance but never phantom power. That's a new one for me.

More important things to worry about dude
More important things to worry about? Higher noise floor, lower headroom (causing the transient clipping I mentioned) and a reduced frequency response? I'm not talking about small differences here either, it can sound like the mic diaphragm is distorting, very obvious. Phantom power is a loose specification and most mics have modest enough requirements that the problem is often not encountered, but condenser mics are like any other piece of electrical equipment - they have a power requirement that if not fulfilled will prevent them from working correctly.
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Old 07-26-2013, 09:09 AM   #13
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I'm looking for a mic that will produce decent results on acoustic guitar as well as vocals. I like the idea of variable patterns, just for the sake of versatility. I'm now looking at the NADY SCM-960. I'm having a bit of trouble finding any decent reviews online, but this mic is only going for 70 bucks, so I could get a pair. 48v, of course, and a 3mA draw sounds a bit safer as far as my devices powering this one. Does anyone have any experience with this mic? Thanks!

http://www.musiciansfriend.com/pro-a...content=review

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Old 07-26-2013, 09:13 AM   #14
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Here is a Phantom Power circuit:

It is NOT a voltage supply (constant voltage) NOR is it a current supply (constant current), but it is a constant voltage fed through a relatively large resistance. The resistor R3 is usually not in the circuit (is a short), and in the schematics I have seen the other two balanced resistors are 4.7K to 6.8K ohms. Since they are in parallel for phantom powering purposes, the effective output resistance of the phantom supply will range from 2350 ohms to 3400 ohms. The Microphone is connected to the LEFT side of the circuit shown. If the microphone presents a short circuit to the phantom power source (48 volts open circuit) the MAXIMUM current available would be 48/2350 = 20.4 milliamps. More realistically, a mic that presents a 2350 ohm load will draw 10.2 milliamps and the voltage measured at the mic connector would drop to 24 volts. Anyone designing a Mic to work with phantom power should be aware of these circuit specs and should design for the expected voltage drop.




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Old 07-26-2013, 09:21 AM   #15
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What does that tell me about the M179? I'm not an electrical engineer by any stretch. If the M179 appears to draw more than my phantom power devices can provide, is it a bad design? Should I avoid it? Will it be fine? I appreciate your knowledge and your help, but I'm not at all hip to applying Ohm's Law to everyday situations. Thanks

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Old 07-26-2013, 09:40 AM   #16
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Edward,


In order to answer your questions I need to know how you measured the phantom current output from your devices. Did you just connect a mA meter from one of the mic pins to ground?

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Old 07-26-2013, 09:46 AM   #17
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I followed the procedure listed on this page:

http://shure.custhelp.com/app/answer...ge-and-current
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Old 07-26-2013, 10:31 AM   #18
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OK - that is a reasonable procedure, and yes, the current measurement is loaded by you mA meter, which should be close to a short. However some meters do have significant resistance in mA mode (up to a few hundred ohms sometimes), which will throw the measurment off a little.

One thing to note is that the Shure procedure given measures the current available from each of the balanced mic connections separately, so the actual current available from the device is the SUM of the currents measured from each side.

Assuming you mA meter is zero ohms then:

..... 44.3V/6.53mA = 6784 ohms output resistance from the mixer.

This is nearly within IEC spec of 48V and 6800 ohms.

The other device = 48.1V/3.5mA = 13743 ohms which is a long way from conforming to the IEC spec.

My expectation is that the CAD microphone designers were aware of the spec (48V and6800 ohms) and designed their Mic to work properly under these conditions. 44.3V is a little low but most Mic manufacturers design with a little MARGIN so I would also expect the CAD to work properly with the voltage 10% low.

You might well have problems with the CAD connected to the UX2 however.

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Old 07-26-2013, 11:00 AM   #19
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Thank you for taking the time. And also for doing math! I hate to subject anyone to that. The CAD looks like a killer mic at that price point, and it sounds like it will work 'OK' with my mixer. My gut is telling me to find something else comparable and avoid future frustrations. If I had to take issue with something, I suppose it would be with the mixer specs. Peavey claims to provide 48v phantom power, but it is clearly not. And I measured with nothing connected to the XLR's as well as at the mic end of the cord. But I suppose that it is what it is. To me, almost anything will be an improvement. As of now, I'm using a borrowed Nady SCM-900, which is ok, but I'd like to hear my guitar mic'd with an omnidirectional mic, just because of the nice reflective sound I get in this room. I fully understand that you get what you pay for in most cases, but if I can find something inexpensive, like the SCM 960 I mentioned, then I could afford a pair which would be even better. I really liked the continuously variable feature of that CAD mic though. Thanks again for your time. It helps a lot.

Edward
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Old 07-26-2013, 11:09 AM   #20
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I sent an email to CAD support listing my power specs. We'll see what they have to say about it. Maybe the power requirements are a bit inflated in the specs. I hope so, anyway. I can follow up here when I get a response if there's any interest.

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Old 07-26-2013, 11:22 AM   #21
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I just got off the phone with a rep from CAD. He uses the exact same Line6 UX2 that I have for his recording, and said he's used the M179 for years with no issues. And that's even with the 3.5 mA on the UX2. He also said that as far as tolerance in the specs, there's a bunch. . So it seems that I was fretting when I shouldn't have been....unless of course he just really wanted to sell me a microphone! Anyway, looks like I'll be fine with the M179. Thanks to all who offered info and assistance!

Edward
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