Phantom Power is a mystery

Posted: Tue Mar 20, 2007 8:38 am

My point was fellas, that there are no manufacturers saying "don't use a 48V phantom power supply, because this mic only needs 15V and you will blow it up", nor are there danger stickers on mics, or legal disclaimers, or reports of smoldering lips or missing facial hair in the news. The circuit in the mic sees the various voltage and applies a constant charge, no matter what that incoming voltage is. That is the point.

Yes, there are mics that will take 52V now. On average, there are fewer mics requiring a full 48V to operate. Go to Shure, AT and other websites and check it out for yourself. As stated, some will get by the 9V. This range of acceptable voltages proves my point again.

Posted: Tue Mar 20, 2007 10:04 am

sheet wrote:

My point was fellas, that there are no manufacturers saying "don't use a 48V phantom power supply, because this mic only needs 15V and you will blow it up", nor are there danger stickers on mics, or legal disclaimers, or reports of smoldering lips or missing facial hair in the news. The circuit in the mic sees the various voltage and applies a constant charge, no matter what that incoming voltage is. That is the point.

Yes, there are mics that will take 52V now. On average, there are fewer mics requiring a full 48V to operate. Go to Shure, AT and other websites and check it out for yourself. As stated, some will get by the 9V. This range of acceptable voltages proves my point again.

I actually responded to (quoted) points you made and disproved them. If your argument is changing do let us know as I was responding to your argument that using 12V phantom power with virtually any Mic is OK.

Quote:

98% of the condsensers made do not require 48Vs. Many will get by on 12V.

As I said in my last post it really depends if you just want to get by, or work to full spec. I also noted in my last post that many of the AKG mic's will work happily down to 9V at full spec. That is simply because they have electret capsules and NOT traditional condenser mic capsules. With the traditional condenser mic's the charge is established by the phantom power. As Q = C * V, as I pointed out before, it essential that the charge is kept constant. This is achieved by feeding the phantom power through a very high impedance (several MegOhms) which effectively creates a low pass filter cutting off BELOW the audio spectrum. As the capacitance of the capsule is determined by the physical size, plate spacing and dielectric constant then the capacitance is in the order of 100pF or so give or take. To achieve sufficient charge to give good noise and overload characteristics then a reasonably high voltage is required - hence the original established 48 V "standard".

Quote:

As stated, some will get by the 9V. This range of acceptable voltages proves my point again.

So how do the manufacturers who quote MINIMUMS of 35V or 44V prove your point? It does no good, as you have already pointed out, to compare apples to oranges. In this case capsules that REQUIRE a polarising voltage and those that don't (Electrets).

For a true condenser mic (NOT electret capsule) then reduced voltage WILL compromise performance. I guess that is why, of the manufacturers I could be bothered to check in my last post, ALL (as opposed to your assertion of NONE) quote a MINIMUM phantom voltage WAY above the 12V that you claim is OK. Of course electret capsules are a completely different kettle of fish as the phantom power is ONLY required to power the buffer amp. If you disagree with this perhaps you should contact the manufacturers to tell them that they are wrong about their own products....

EDIT: You asked us to check out Shure as an example - KSM9 spec is 48V +/- 4V. Tell me again how this proves your point?

EDIT2: What the hell, I've also checked the AT site -AT2020, AT3035 etc are electrets. AT 4047, AT4050 are conventional but unsurprisingly require 48V (no tolerance given unlike the 3035 at 11V - 52V.)

I make that 5 different manufacturers including two of your own suggestion - have I proven the point yet?

Posted: Mon Mar 26, 2007 11:53 pm

This is completely awesome! You know everybody, this has been one of the best discussions I've had the pleasure of reading in the over 1 1/2 years I've been on the forum!

Those of us with a few years under our belts/skirts, all have had interesting experiences regarding the powering of condenser microphones. KIDS, DON'T TRY THIS AT HOME. I think both right and wrong, there are many valid points here. Many people have mentioned things that I had completely forgotten about! And it brought to mind the time, I think back in 1978, I was using a rented Sennheiser MKH815 (?) the long shotgun microphone and a Nagra IV on a industrial film shoot, where Sennheiser was utilizing AB powering for that microphone, which wasn't PHANTOM. It had a external portable battery pack and I don't remember the voltage? But it was not phantom. So, does anybody remember AB?? I don't remember T powered microphones? It must be my missing brain cells?

And along with my missing brain cells, I think that few people also know (except for a very few) that many of the Neumann microphones actually have output pads in their output circuits? Really. Check their schematics. They have, throughout time, been able to offer up more output than most preamps can deal with. I know that my old KM56, U67's, U87's are that way. I've never bothered to take the output pads, out. I even believe it's mentioned in their original supplied data sheets? I'm too lazy to go searching for mine right now. Not sure why I never bothered to try? Probably because they were/are Neumann's? You don't fix it if it ain't broke.

I actually had/have a different kind of problem when trying to phantom power microphones. When you are doing remotes, from a truck, from 250 to 500 or more feet away, that 48 volts, even coming from the Neve gets rather anemic at that distance. In those situations, I always had planned to build a power supply to be placed down at the stage, in the transformer split box, so the power supply was closer to the microphones. DC just doesn't travel as robustly as AC. Unfortunately, the road to hell is paved with good intentions. I never got to building the power supply in the split box. Go figure?

Consistently inconsistent
Ms. Remy Ann David

Posted: Tue Mar 27, 2007 8:24 am

RemyRAD wrote:

I actually had/have a different kind of problem when trying to phantom power microphones. When you are doing remotes, from a truck, from 250 to 500 or more feet away, that 48 volts, even coming from the Neve gets rather anemic at that distance. In those situations, I always had planned to build a power supply to be placed down at the stage, in the transformer split box, so the power supply was closer to the microphones. DC just doesn't travel as robustly as AC. Unfortunately, the road to hell is paved with good intentions. I never got to building the power supply in the split box. Go figure?

Hi Remy,

I'm not at all sure this problem is due to losing voltage on your phantom power as you seem to think. As phantom power is fed on the balanced lines, it is necessary for the phantom voltage to be fed through resistors so that the input impedance of the amplifier is not seriously compromised. These resistors are usually several kOhms as they MUST be larger than the input impedance of the pre-amp. If no buffer is present in the Mic then, once the capsule is polarised, there will be virtually no current drawn and the capsule will get the full source phantom voltage. Mics that power a buffer amp from the phantom voltage have an increased current consumption and there will be a consequent drop in the output voltage from the console.

In either case, even with a very long cable run, you should not have more than a few Ohms resistance in the cable which is effectively in series with the several kOhms of phantom source impedance. The result is the phantom voltage should not be seriously compromised by long cable runs. My guess is that if performance is compromised by a long cable run it is an effect of the cable capacitance loading the buffer and not "anaemic" phantom voltage.

Pre-amp and console manufacturers rarely seem to specify the series resistance of their phantom power but remember it MUST be more than the quoted input impedance of the pre-amp. The only saving grace is that both lines carry the phantom power so the series resistors end up effectively in parallel.

EDIT: I just did a quick test on my ageing Yamaha 01V. Phantom was 48.4V with no load and 33V with a 10k load (on hot input). This gives the series resistance (per side) of 4.7 kOhm, which will mean a source impedance of 2.35k when paralleled with the cold input. This is fairly typical as the specified input impedance for the board is 3kOhm. Unless there is something seriously wrong with your cable then the cable impedance, even on a long run, will have little relevance to the actual phantom power arriving at the Mic. Also note that many electret Mic's will draw around 3 mA (for the buffer amp). This is close to the 3.3mA load my test gave, so with such a Mic will only give phantom power of around 41V even with a very short lead.

EDIT 2:

Quote:

DC just doesn't travel as robustly as AC.

I would have said the opposite was true. They both have to contend with the cable resistance but true DC does'nt care about capacitance and inductance like AC does! :<)

Posted: Tue Mar 27, 2007 3:54 pm

hi there folks, i'm new here. My name is Louise and i'm from Scotland.

I recently purchased a condenser mic and found i had this phantom power problem too. I've been offered a Behringer tube ultragain t1953 mic preamp at a very reasonable price. Would that do the business?

Posted: Tue Mar 27, 2007 4:26 pm

fabian-lou wrote:

hi there folks, i'm new here. My name is Louise and i'm from Scotland.

I recently purchased a condenser mic and found i had this phantom power problem too. I've been offered a Behringer tube ultragain t1953 mic preamp at a very reasonable price. Would that do the business?

Hi Louise, and welcome!

Can you describe what you mean by "this phantom power problem" and "do the business"? Also, if you are serious about recorded sound quality, I think you can do better than a T1953, though it would probably mean spending a bit more.

Posted: Tue Mar 27, 2007 4:38 pm

Basically I bought a condenser mic and because I'm very new to recording I didn't realise I couldn't just plug it in and go! My band and I aren't after anything too flashy and I just wanted to know if I were to buy the T1953, I wouldn't need to buy anything else to at least get sound out the mic right?

Posted: Tue Mar 27, 2007 5:16 pm

fabian-lou, just a little advice to somebody that is new to this stuff. I really don't think you want a tube condenser microphone. What you might want to look at are some of the fine Audio Technica line of condenser microphones. Many of them accept AA batteries and would be much more practical as you do not need to deal with a short microphone cord to a bulky external power supply that requires 117 volts. That's just selling for somebody that's starting out. And I would also assume, you might want to use this in some live, PA oriented situations? In which case, you really don't want to use that tube condenser microphone but rather a compact back electret, battery-powered studio condenser microphone.

That tube condenser microphone, comes later when you think you might want that kind of sound. Besides, the smaller capsule of the condenser microphones such as I've recommended, actually have a brighter cleaner sound with extended high-frequency response that has a nice airy quality. Where the tube microphone is darker and mushier but not always. Think about obtaining at least 1 Shure SM 58? Wonderful sounding, very versatile, requires no power supply, can hammer nails and only costs $100 US. A very smart investment for a beginner.

Not a beginner
Ms. Remy Ann David

Posted: Tue Mar 27, 2007 6:43 pm

MrEase wrote:

sheet wrote:

My point was fellas, that there are no manufacturers saying "don't use a 48V phantom power supply, because this mic only needs 15V and you will blow it up", nor are there danger stickers on mics, or legal disclaimers, or reports of smoldering lips or missing facial hair in the news. The circuit in the mic sees the various voltage and applies a constant charge, no matter what that incoming voltage is. That is the point.

Yes, there are mics that will take 52V now. On average, there are fewer mics requiring a full 48V to operate. Go to Shure, AT and other websites and check it out for yourself. As stated, some will get by the 9V. This range of acceptable voltages proves my point again.

I actually responded to (quoted) points you made and disproved them. If your argument is changing do let us know as I was responding to your argument that using 12V phantom power with virtually any Mic is OK.

Quote:

98% of the condsensers made do not require 48Vs. Many will get by on 12V.

As I said in my last post it really depends if you just want to get by, or work to full spec. I also noted in my last post that many of the AKG mic's will work happily down to 9V at full spec. That is simply because they have electret capsules and NOT traditional condenser mic capsules. With the traditional condenser mic's the charge is established by the phantom power. As Q = C * V, as I pointed out before, it essential that the charge is kept constant. This is achieved by feeding the phantom power through a very high impedance (several MegOhms) which effectively creates a low pass filter cutting off BELOW the audio spectrum. As the capacitance of the capsule is determined by the physical size, plate spacing and dielectric constant then the capacitance is in the order of 100pF or so give or take. To achieve sufficient charge to give good noise and overload characteristics then a reasonably high voltage is required - hence the original established 48 V "standard".

Quote:

As stated, some will get by the 9V. This range of acceptable voltages proves my point again.

So how do the manufacturers who quote MINIMUMS of 35V or 44V prove your point? It does no good, as you have already pointed out, to compare apples to oranges. In this case capsules that REQUIRE a polarising voltage and those that don't (Electrets).

For a true condenser mic (NOT electret capsule) then reduced voltage WILL compromise performance. I guess that is why, of the manufacturers I could be bothered to check in my last post, ALL (as opposed to your assertion of NONE) quote a MINIMUM phantom voltage WAY above the 12V that you claim is OK. Of course electret capsules are a completely different kettle of fish as the phantom power is ONLY required to power the buffer amp. If you disagree with this perhaps you should contact the manufacturers to tell them that they are wrong about their own products....

EDIT: You asked us to check out Shure as an example - KSM9 spec is 48V +/- 4V. Tell me again how this proves your point?

EDIT2: What the hell, I've also checked the AT site -AT2020, AT3035 etc are electrets. AT 4047, AT4050 are conventional but unsurprisingly require 48V (no tolerance given unlike the 3035 at 11V - 52V.)

I make that 5 different manufacturers including two of your own suggestion - have I proven the point yet?

Call the manufacturer's engineers and ask them what is the lowest voltage that the mic will tolerate. They ALL have a number, most of them less than 48V. The 48V number is an indication as to the maximum. Shure does give a variance on some mics +/-4 in some cases. There are hordes of consoles out there that do not put out 48V, and condensers work with them all of the time.

Think about this now. According to Shure, the SM94's internal battery will last 5,000 hours. Now either they have some KILLER battery technology that puts out a full 48V for 5,000, or that mic doesn't need a full 48V to operate. I suspect that I am correct and you are not. Better yet, call them for yourself.

The phantom power listings on most mics are the MAX allowed, not the exact amount.

Posted: Tue Mar 27, 2007 6:46 pm

RemyRAD wrote:

This is completely awesome! You know everybody, this has been one of the best discussions I've had the pleasure of reading in the over 1 1/2 years I've been on the forum!

Those of us with a few years under our belts/skirts, all have had interesting experiences regarding the powering of condenser microphones. KIDS, DON'T TRY THIS AT HOME. I think both right and wrong, there are many valid points here. Many people have mentioned things that I had completely forgotten about! And it brought to mind the time, I think back in 1978, I was using a rented Sennheiser MKH815 (?) the long shotgun microphone and a Nagra IV on a industrial film shoot, where Sennheiser was utilizing AB powering for that microphone, which wasn't PHANTOM. It had a external portable battery pack and I don't remember the voltage? But it was not phantom. So, does anybody remember AB?? I don't remember T powered microphones? It must be my missing brain cells?

And along with my missing brain cells, I think that few people also know (except for a very few) that many of the Neumann microphones actually have output pads in their output circuits? Really. Check their schematics. They have, throughout time, been able to offer up more output than most preamps can deal with. I know that my old KM56, U67's, U87's are that way. I've never bothered to take the output pads, out. I even believe it's mentioned in their original supplied data sheets? I'm too lazy to go searching for mine right now. Not sure why I never bothered to try? Probably because they were/are Neumann's? You don't fix it if it ain't broke.

I actually had/have a different kind of problem when trying to phantom power microphones. When you are doing remotes, from a truck, from 250 to 500 or more feet away, that 48 volts, even coming from the Neve gets rather anemic at that distance. In those situations, I always had planned to build a power supply to be placed down at the stage, in the transformer split box, so the power supply was closer to the microphones. DC just doesn't travel as robustly as AC. Unfortunately, the road to hell is paved with good intentions. I never got to building the power supply in the split box. Go figure?

Consistently inconsistent
Ms. Remy Ann David

AB is another name for T Power

Posted: Wed Mar 28, 2007 5:15 am

sheet wrote:

Call the manufacturer's engineers and ask them what is the lowest voltage that the mic will tolerate. They ALL have a number, most of them less than 48V. The 48V number is an indication as to the maximum. Shure does give a variance on some mics +/-4 in some cases. There are hordes of consoles out there that do not put out 48V, and condensers work with them all of the time.

Think about this now. According to Shure, the SM94's internal battery will last 5,000 hours. Now either they have some KILLER battery technology that puts out a full 48V for 5,000, or that mic doesn't need a full 48V to operate. I suspect that I am correct and you are not. Better yet, call them for yourself.

The phantom power listings on most mics are the MAX allowed, not the exact amount.

I really wish you would read my posts on this again. I think I have made it quite clear with both references to manufacturers data and the engineering behind these Mic's exactly why what you are saying is misleading - I think mainly to yourself. YES I agree with you that many Mic's will operate at lower voltages but I have also explained via manufacturers data and by the engineering that the Mic WILL NOT PERFORM TO SPECIFICATION. at these lowered voltages UNLESS the manufacturer includes the lower voltage in their operating range.

I have referenced 5 different manufacturers for you, ALL OF WHICH quote minimum voltages for their non electret condenser mic's. They quote this minimum for a reason (which I have explained fully). Your apparent refusal to acknowledge this when you continue with your claims is tiresome and you it seems you are intent on not only misleading yourself but trying to mislead others as well.

CHALLENGE!

If you still disagree please post solid engineering reasons why just ONE of any Mic's you choose will work perfectly at voltages BELOW the manufacturers spec. As I have already given references to many and explained why, this should not be too much to ask. Please do not include an electret design as I have already explained the differences and as you say yourself we don't want to compare apples and oranges.

EDIT: BTW the SM94 has an electret capsule. Long battery life is easy as no 48V is necessary and only the buffer amp needs to be powered. Again your argument is comparing the apples and oranges you told us to avoid - thus making your point a bit of a lemon!

Posted: Wed Mar 28, 2007 8:13 am

You're right in that I did not read all of the posts. No time in the day for that.

My original point was recognized by you, so I will drop it. We are both saying the same things, just not clearly. I said before that not all condensers require a full 48V phantom, there are multiple voltages as standard. I stated brands like Peavey, Behringer, and other contract/paging manufacturers have products that are not a full 48V, because there mics and a vast number of others (by their ressearch, not mine) operate on a lower voltage than 48V. Yes, some manufacturers state that they need a full 48V, others state that as a max. Shure has done both. Consider the Beta87. It now says 52V max. They list variances on some, not on others. The ones without variances are electrets and sometimes have battery power.

You mentioned AT as an example. I just spoke to Scott at AT. He validated my position. Just because some of their mics say 48V, does not mean that the circuit does not step the voltage down. There are some mics that require a full 48V, but will accept as much as 52V. The Unipoint and Engineered lines will accept 11-52V, and perform to spec at any giving voltage. One of the engineers, Jim, reemphasized the point that they design for optimum performance with a +/-2V on their studio mics that require 48V, but those variances are not published.

Again, in the context of the average user who visits this forum, all of this crap is over their heads. They want to know if phantom is needed, will it blow up a dynamic, how much phantom is needed, etc. It is confusing to them because mixers sometimes have phantom on all of the time, it is switchable in banks of eight, or they must use outboard supplies. This is the reason that I answer the way that I do, to answer all of the questions before it becomes a long thread.

I stand behind what I said. My definitions of phantom and the operations of mics are supported by industry sources, three of which are Rane's Pro Audio Reference, DPA and Marty McCann (in reference to the Peavey stuff).

There is NAMM sales data to support what I said about the majority of mics operating on 12V or 24V phantom. Again, no two manufacturers measure mic performance the same way, or list stats the same way.

Because few mics use raw phantom, and because no mic applies it directly to the backplate/diaphragm, most any mic will take 48V. Most any mic that does not list an operational variance (+/- something) WILL perform to spec. It is the internal circuit that determines what the voltage should be, and performance of the mic does not increase if it is GREATER, because the voltage via the mics performance remains constant.

Posted: Wed Mar 28, 2007 9:37 am

sheet wrote:

You're right in that I did not read all of the posts. No time in the day for that.

My original point was recognized by you, so I will drop it. We are both saying the same things, just not clearly. I said before that not all condensers require a full 48V phantom, there are multiple voltages as standard. I stated brands like Peavey, Behringer, and other contract/paging manufacturers have products that are not a full 48V, because there mics and a vast number of others (by their ressearch, not mine) operate on a lower voltage than 48V. Yes, some manufacturers state that they need a full 48V, others state that as a max. Shure has done both. Consider the Beta87. It now says 52V max. They list variances on some, not on others. The ones without variances are electrets and sometimes have battery power.

You mentioned AT as an example. I just spoke to Scott at AT. He validated my position. Just because some of their mics say 48V, does not mean that the circuit does not step the voltage down. There are some mics that require a full 48V, but will accept as much as 52V.

I find it somewhat of an insult and waste of my time when I make fully valid points and you do not bother to read them properly. Yet you continued to take me to task with red herrings, as in the last example.

I have also explained already that some AT Mic's (exclusively Electret) do not require the full 48V phantom power and if you read my response to Remy re- phantom power you will see how many of these mic's will significantly drop the 48V anyway.

As I have already said and has been my main contention, I think it is ill advised to make comments like:

sheet wrote:

98% of the condsensers made do not require 48Vs. Many will get by on 12V.

Whilst it may, just, be possible that 98% of sales will be with what is still often regarded as the low end market of Electret Mic's I am certain that the statistic is not true for all Mic models that are currently available, as I have already pointed out (and provided references for). Do you have a link to that NAMM data so I can confirm?

The quote above could easily convince a newcomer that he would be extremely unlucky if he bought equipment that did not match but sooner or later it would be certain to happen. It would have been MUCH wiser IMHO to advise them to check the specifications first or at least ask around here for advice before parting with cash - much as it seems Louise has unfortunately done already.

Posted: Wed Mar 28, 2007 10:50 am

No link to NAMM data. The data that I was given was compiled from various sales reports. Since you must be a member of NAMM to obtain the info, I doubt that there is a link. I will check with a few people to see how/where they got their data specifically.

It should not matter. The fact that companies engineer, build and sell products with this capability should be documentation enough that there is justifiable cause for it in the MI market. Multiple manufacturers obviously know who their customers are, and what they will likely buy to use with their products.

Posted: Wed Mar 28, 2007 5:08 pm

sheet wrote:

You're right in that I did not read all of the posts. No time in the day for that.

My original point was recognized by you, so I will drop it. We are both saying the same things, just not clearly. I said before that not all condensers require a full 48V phantom, there are multiple voltages as standard.

I have no idea why you seem to think we are now in agreement.

sheet wrote:

I stated brands like Peavey, Behringer, and other contract/paging manufacturers have products that are not a full 48V, because there mics and a vast number of others (by their ressearch, not mine) operate on a lower voltage than 48V. Yes, some manufacturers state that they need a full 48V, others state that as a max. Shure has done both. Consider the Beta87. It now says 52V max. They list variances on some, not on others. The ones without variances are electrets and sometimes have battery power.

Nowhere on this entire thread have you made any comment about "Peavey, Behringer, and other contract/paging manufacturers" except where you claim you have - unless you now go back and now edit your older posts to rectify this.

Really your points are like shifting sands and I frankly give up. You clearly have not grasped the point of what I have been saying. If you had the courtesy to actually read my input on this thread you might understand my points and also how these things work. You might also better appreciate the practical differences in design and phantom power requirements of electret mic's and non polarised types.

I have actually given quite a bit of information. Maybe you should get Scott at AT to look at the thread and add his own comment.

As far as I am concerned, I think you have given some rash advice which I have disproved with full explanations (based on 30 years of design experience - so I'm no "noob" to this) and references. I have not taken irrelevant data and tried to use it to support my argument (cf. apples and oranges). I stand by every point I have made and I think I have given ample information so at least others can read this thread and make their own decisions.