I was hoping someone could explain why a large diaphragm condsenser mic needing 48v, worked just fine today when I plugged it into an UltraSound AG-50DS4 acoustic amplifier at a music store when the amp is rated as only driving 15v for the XLR input ?
What is going on here ? Is there a problem hidden around the corner ?
Anybody ?
Bret
RemyRAD Moderator
Joined: Sep 26, 2005
Posts: 3124
Location: Washington DC Virginia suburbs
Ahhhhhhhhhhh grasshopper you have found the hidden power within the Phantom.
What's really happening here is that the original true condenser microphone required 48 volts to polarize the diaphragm. These were the original type microphones that Neumann and other manufacturers originally made. They would not work on any less than 48 volts.
Enter the lower-cost, permanently polarized "back electret" condenser microphones. Originally these were not of the quality of the non-polarized 48 volt requirements of the non-polarized diaphragms. Over the years, technology has improved greatly on these permanently polarized "back electret" condenser microphones that can operate on voltages as low as 1 1/2 volts or a single AA battery, that operates the little single transistor impedance converter as opposed to having to polarize the diaphragm.
So if you had tried to plug in a higher-quality original Neumann that required 48 volts to polarize the diaphragm, it would not have worked with that 15 volts supply as most inexpensive condenser microphones can. So there is no problems around the corner if you do not purchase a microphone that requires a true 48 volt full phantom supply. So if a condenser microphone happens not to work, such as the very inexpensive Nady, Samson and others, it is because they have a non-polarized diaphragm that requires 48 volts, to polarize the diaphragm.
So you must always pay close attention to what the power requirements are for any condenser microphone you purchase.
So you should not necessarily be intimidated by a back electret condenser microphone since one of the finest test and calibration microphones made by (formerly) "B&K" (Danish names too difficult to pronounce for Americans Bruel & Kajier or something like that) now known as "DPA" for Danish Pro Audio are very high in cost, quality, response and specifications and are in fact, back electret condenser microphones. Same as what you get at Radio Shaft but not really! A beautiful example of cost versus quality. You can actually get exceptionally good sounding condenser microphones from Radio Shaft, since their Taiwanese supplier of back electret capsules is the same supplier that makes the capsules for the superb sounding Crown series of condenser microphones. It's a crapshoot from Radio Shaft. You might get a good sounding one? You might not. Back in the early 1990s, I purchased 10 PZM's and out of that 10, 2 of them sounded like crap. So I gave those two, to an amateur recording enthusiast friend, who loved them.
You have to play to win.
Ms. Remy Ann David
ghellquist Recording Org Pro Audio Group
Joined: May 14, 2004
Posts: 616
Location: Stockholm, Sweden
Actually,
I think that ms Remy is off on this one. Even "true" condensor mics (whatever that is, here I mean externally polarized) can work at or even below 15Volts. It all depends on the exact setup of the electronics inside the mic.
The capsule will work fine with only 15V of external polarization. It will still create an output signal. And this signal will be amplified by the internal amplifier. Many of the chinese mics use a similar circuit where a 12V zener diode is used to create the "mid-point". This means that they will work down to about 13 or 14V somewhere before finally cutting out.
There is a penalty to pay though, or to be exact two. Firstly the output signal will be sligthly lowered due to the the lower polarizing voltage. Secondly maximum SPL before clipping will be lower, mostly due to the electronics.
There are top quality condensor mics specially made to the rather unusual 12V phantom standard, Schoeps CMC6 amplifier comes to my mind as a splendid example. Avoid feeding these anything not following either the 12V or the 48V phantom standard (they autoswitch, but do not like things in between).
Small diameter Neumanns (say KM184) are not happy and simply stops working (they are not harmed in my experience) below about 40V. The KM184 actually has a voltage converter creating about 60V as polarizing voltage for the capsule and I think it stops running.
Other mics may be damaged by voltages not following specs, you have to check your mic manufacturer. All mics I know of dislike too high phantom voltage (max is 52V without mic connected) so don´t go that road.
Gunnar
ghellquist Recording Org Pro Audio Group
Joined: May 14, 2004
Posts: 616
Location: Stockholm, Sweden
B&K still exists. They spun off their professional (as in studio use) mic division into a separate company DPA a number of years ago. I think that the markets where too different to work on. DPA mics are very good, I love my pair. But if you think they are expensive, look at what some certified measurement mics costs!
There is a penalty to pay though, or to be exact two. Firstly the output signal will be slightly lowered due to the the lower polarizing voltage. Secondly maximum SPL before clipping will be lower, mostly due to the electronics.
I'd add to that the linearity of the preamp will likely be different - especially if it uses a FET, since the biasing will change the transfer characteristics of the device. If the biasing is significantly different, the even harmonic distortion content may increase dramatically - even at moderate SPL. You may or may not like the sonic difference.
sheet Moderator
Joined: May 28, 2003
Posts: 886
Location: Kansas City, KS
Ahhhhhhhhhhh grasshopper you have found the hidden power within the Phantom.
What's really happening here is that the original true condenser microphone required 48 volts to polarize the diaphragm. These were the original type microphones that Neumann and other manufacturers originally made. They would not work on any less than 48 volts.
Enter the lower-cost, permanently polarized "back electret" condenser microphones. Originally these were not of the quality of the non-polarized 48 volt requirements of the non-polarized diaphragms. Over the years, technology has improved greatly on these permanently polarized "back electret" condenser microphones that can operate on voltages as low as 1 1/2 volts or a single AA battery, that operates the little single transistor impedance converter as opposed to having to polarize the diaphragm.
So if you had tried to plug in a higher-quality original Neumann that required 48 volts to polarize the diaphragm, it would not have worked with that 15 volts supply as most inexpensive condenser microphones can. So there is no problems around the corner if you do not purchase a microphone that requires a true 48 volt full phantom supply. So if a condenser microphone happens not to work, such as the very inexpensive Nady, Samson and others, it is because they have a non-polarized diaphragm that requires 48 volts, to polarize the diaphragm.
So you must always pay close attention to what the power requirements are for any condenser microphone you purchase.
So you should not necessarily be intimidated by a back electret condenser microphone since one of the finest test and calibration microphones made by (formerly) "B&K" (Danish names too difficult to pronounce for Americans Bruel & Kajier or something like that) now known as "DPA" for Danish Pro Audio are very high in cost, quality, response and specifications and are in fact, back electret condenser microphones. Same as what you get at Radio Shaft but not really! A beautiful example of cost versus quality. You can actually get exceptionally good sounding condenser microphones from Radio Shaft, since their Taiwanese supplier of back electret capsules is the same supplier that makes the capsules for the superb sounding Crown series of condenser microphones. It's a crapshoot from Radio Shaft. You might get a good sounding one? You might not. Back in the early 1990s, I purchased 10 PZM's and out of that 10, 2 of them sounded like crap. So I gave those two, to an amateur recording enthusiast friend, who loved them.
You have to play to win.
Ms. Remy Ann David
Actually, the oldest Neumann mics came with power supplies that did more than phantom, and none of them had standard three pins that we have now. They had internal amplifiers that had line level outputs. For a long time in broadcast consoles, there was no in console mic preamplifier.
You don't really need to be careful with anything. Except to make sure that if you do have a mic that needs a full 48V (and I doubt you do), that your power supply is stable.
The standards for phantom power are this: 12V, 24V, 48V. The above mentioned DPAs do not use High Voltage supplies to power the diaphragm. The high voltage mics will not work with just any preamp either. DPA used those high voltages to power an amplifier circuit alone inside the mic, yielding better performance.
Unless your mixer says "48V", then it is not putting out 48V. Not all manufacturers abide by the standards mentioned above either. Many MI mixers have 15V supplies. Generally speaking, the cheaper the mixer, the more unstable the phantom power is. If you have unstable phantom, them you will have a decrease in mic sensitivity, output and hence more noise. If you use any of those funky mic cables that light up, or those inline noise gates, you will need to deduct their consumption from the available voltage, to see if your mic will still work.
98% of the condsensers made do not require 48Vs. Many will get by on 12V. All non DPA HV mics will tolerate a maximum of 48V. So you will not harm a mic that only needs 12V by giving it 48V.
98% of the condsensers made do not require 48Vs. Many will get by on 12V. All non DPA HV mics will tolerate a maximum of 48V. So you will not harm a mic that only needs 12V by giving it 48V.
This is dangerous advice.
Microphone designers work to a specification. If in order to meet the specified performance they need 48V +/-4V phantom power, then trying to run the microphone off 12V will mean at the very least it will not meet the specification. It may appear to work, but be compromised at higher sound levels, or may not be capable of driving 100ft of cable, or whatever.
More serious is applying a higher power supply voltage than the maximum specified. You should never do this to a microphone, pre-amp, channel strip or anything electronic. The designer has produced the design to work within the specified voltage tolerances, used components to be compatible with that voltage and made arrangements to deal with the resulting heat dissipation. Applying higher voltages may cause component breakdown and localised overheating, which, if not immediately apparent, is likely to curtail the active life of the unit. Heat dissipation rises as the square of the voltage in a resistive load.
Sorry about the rant, but speaking as a professional electronic designer, I would be sad to have to put overvoltage crowbars in all my product designs so that the fuse in the power supply blows whenever some ill-advised user puts 4 times the rated voltage on the power rails.
MrEase Recording Org Pro Audio Group
Joined: Jan 19, 2006
Posts: 46
Location: Surrey, UK
All condenser Mic's (whether electret or non polarised) work on the same very basic principle.
Q (Charge) = C (capacitance) * V (Voltage).
With non polarised types, the phantom power is responsible for establishing the Charge and the sound wave modulates the Capacitance which hence modulates the Voltage and gives us the Mic output. If we rearrange the formula we get
V = Q/C.
If we use 48 V this will establish a certain charge on the Mic. If we use 12 V then there will be 1/4 of the charge on the Mic and therefore 1/4 of the output. This does not take into account the amplifier, which will normally be worse performing at lower voltages. The net result is that at 12V the output will be 6 dB down AND the noise floor may well be worsened as too will be the dynamic range of any internal preamp.
It is altogether NOT a good idea to run condenser Mic's at lower than their intended phantom voltage. In most cases though they will still work to an extent but certainly not to the published Spec.
JoeH Moderator
Joined: Jun 22, 2004
Posts: 1779
Location: Philadelphia, PA
well said; When it comes to phantom power & voltages, this is another case of "Just because you CAN doesn't mean you should."
Good to remember that in these times of affordable stuff that cuts corners here and there, even in times of necessity (like portable/field use gear) it's always best to start out with the real deal.
220, 221, whatever it takes.
_________________ Joe Hannigan, Producer
WestonSound.com - Philadelphia, PA
Acoustic Music Forum co-moderator.
sheet Moderator
Joined: May 28, 2003
Posts: 886
Location: Kansas City, KS
98% of the condsensers made do not require 48Vs. Many will get by on 12V. All non DPA HV mics will tolerate a maximum of 48V. So you will not harm a mic that only needs 12V by giving it 48V.
This is dangerous advice.
Microphone designers work to a specification. If in order to meet the specified performance they need 48V +/-4V phantom power, then trying to run the microphone off 12V will mean at the very least it will not meet the specification. It may appear to work, but be compromised at higher sound levels, or may not be capable of driving 100ft of cable, or whatever.
More serious is applying a higher power supply voltage than the maximum specified. You should never do this to a microphone, pre-amp, channel strip or anything electronic. The designer has produced the design to work within the specified voltage tolerances, used components to be compatible with that voltage and made arrangements to deal with the resulting heat dissipation. Applying higher voltages may cause component breakdown and localised overheating, which, if not immediately apparent, is likely to curtail the active life of the unit. Heat dissipation rises as the square of the voltage in a resistive load.
Sorry about the rant, but speaking as a professional electronic designer, I would be sad to have to put overvoltage crowbars in all my product designs so that the fuse in the power supply blows whenever some ill-advised user puts 4 times the rated voltage on the power rails.
First of all, you have no idea what you are talking about, Second, I would appreciate it if you would edit your message, removing the "dangerous" advice comment.
So, you are saying that you should never use a 12V or 15V mic on a 48V source? Show me ONE mic manufacturer that specifies a cap voltage for their condensers mics. There aren't any. Show me ONE console or preamp manufacturer that offers variable phantom power ouputs. There aren't any.
Few if any mics run completely from raw phantom. Mics use 5V or more to drive a low V zener that determines the polarization voltage and powers the electronics. They are powered from a fixed and regulated low voltage source inside the mic. Increasing the phantom power voltage is never seen by the microphone element or electronics, it only increases the voltage across the current source.
Exactly. Those microphones will say in their specification something like "phantom power 12V - 52V", because they have been designed to work over that voltage range. Some may also say that the max SPL is lower at 12V than at 48V.
If a piece of equipment, for example a T-power microphone, says "power source 12V" on it, you don't connect it to 48V. Your post said "you will not harm a mic that only needs 12V by giving it 48V". My comment stands.
sheet Moderator
Joined: May 28, 2003
Posts: 886
Location: Kansas City, KS
Dude, you are not comparing apples to apples. The only way that a T-Power mic works is if it is connected to something that accommodates it in the field recording industry. Even a 58 would be destroyed probably being hooked up to a T-Power source.
My comment still stands, and is supported throughout the industry. You are referencing another niche powering option for something that is beyond the scope of the OP.
Few if any mics run completely from raw phantom. Mics use 5V or more to drive a low V zener that determines the polarization voltage and powers the electronics. They are powered from a fixed and regulated low voltage source inside the mic. Increasing the phantom power voltage is never seen by the microphone element or electronics, it only increases the voltage across the current source.
Interesting. A Zener isn't the greatest regulator in the world - not very low impedance. Is it standard practice to use the same voltage source point for both preamp power and polarization? I would think that could cause some nasty non-linearities if that is the case. Or, are some using a zener and others a true, low-noise, low-z regulator?
sheet Moderator
Joined: May 28, 2003
Posts: 886
Location: Kansas City, KS
Now I don't really want to get involved in the dispute between Boswell and Sheet but......
Quote:
Show me ONE mic manufacturer that specifies a cap voltage for their condensers mics. There aren't any.
OK then. I went to the first site in my favourites which just happened to be Rode and the first Mic I looked up the spec on (Rode NT2000) said Phantom Power "P48" which means 48V nominal. The second (NT1000) said P48 (35V- 53V) so it even specified the limits. I don't see much point in going further as by pure chance I have a 100% hit rate as a rebuttal of your statement.
Quote:
98% of the condsensers made do not require 48Vs. Many will get by on 12V.
I have no idea where you got this statistic. Please provide a link otherwise I will have to assume it is your own assessment. The previous argument I made is already indicating that the "statistic" may well be untrue.
The bottom line is that the physics is very much as I stated in my previous post. I see little point in going into greater detail than the earlier post. No Mic manufacturer has yet found a way round the fundamental physics. So while, for example, a Rode NT1000 may well "get by" at 12V it is being undoubtably used outside the manufacturers spec. Do not expect the sensitivity, noise figure or overload margin quoted for the mic!
Funny, I thought I made the point earlier!
EDIT: Add all of the AKG range to those that specify the phantom power even though most are electret types that will work from 9V - 52V, the C414 is NOT!
EDIT2: My goodness, so do the SE electronics range (48V +/- 4V). Where DID you get your information sheet?
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