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Author Topic: Condenser Mike w/o Power Source???  (Read 3471 times)

ArtRock

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Condenser Mike w/o Power Source???
« on: November 26, 2005, 11:53:30 am »

I've been wondering about this for awhile... Rolling Eyes I have an old Grundig GCM3 microphone which I have several times seen designated as a condenser mike. However, there are no internal batteries and only a single conductor shielded cable. The mike works in a high impedance input without any external power source. I have always thought that ANY condenser mike requires SOME sort of power to operate, so I assumed that the references I had seen stating the GCM3 was a condenser microphone were false. However, I recently saw one for sale on eBay that showed paperwork that came with the mike which states that it IS a condenser mike. Can someone enlighten me here??? Here are some photos of the rather large element of this mike. Although it may not be apparent in the photo, there is a thin, clear film as the first layer on the front of the element.
index.php/fa/1927/0/
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Greg Youngman

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Re: Condenser Mike w/o Power Source???
« Reply #1 on: November 26, 2005, 02:00:40 pm »

I had one of those on a Grundig tape recorder in the early 60's.  I believe it had a DIN connector.  Not a condenser.  I believe it was either a ceramic or crystal element and sounded similar to an Astatic D-104.
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ArtRock

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Re: Condenser Mike w/o Power Source???
« Reply #2 on: November 26, 2005, 02:12:01 pm »

Hi Greg! Thanks for the response. Well that's what I thought, perhaps Grundig was wrong. Below is a pic of the paperwork that came with the mike on eBay...

index.php/fa/1928/0/

Confusing, to say the least.
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ArtRock

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Re: Condenser Mike w/o Power Source???
« Reply #3 on: November 26, 2005, 11:56:00 pm »

So.... Nobody knows whether there could be a condenser mike with no power requirements? Perhaps there is a better forum for such posts? Oh well......................... Shocked
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compasspnt

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Re: Condenser Mike w/o Power Source???
« Reply #4 on: November 27, 2005, 12:09:21 am »

I don't know for sure, but you will get an answer here.

I think it's possible that it is not a true condenser.
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Barry Hufker

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Re: Condenser Mike w/o Power Source???
« Reply #5 on: November 27, 2005, 12:33:28 am »

Figuring the microphone to be an electret condenser, here then is an excerpt from this website: http://www.k-bay106.com/history.htm

Work on the electret condenser microphones dates back to as early as 1928. These microphones used permanently polarized wax plates. Eventually, microphones with wax electrets were offered commercially by Bogen (1938 to 1940) under the name No-Voltage Velotron. The first large-scale application of electric transducers was during WWII, when wax-electret microphones were used in Japanese field equipment. The wax-electrets, however, did not catch on due to their instability and very small capacitance which complicates the mic-preamp design. From 1948 through the early 1960s, work continued in electret microphone technology, turning up materials such as acrylics, ethyl cellulose, polystyrene, vinyl polymers, and ceramic electrets.

In 1962 and 1965 electret microphones in which the diaphragm was composed of a metalized thin foil of Mylar or Teflon, respectively, which has been converted into an electret were proposed. Finally, in 1968, Sony brought out the finest electret condenser microphone. Later, around 1971, Primo Company Ltd. introduced an electret mic with a monolithic IC preamp. Foil-electrets are manufactured in countless numbers; the Japanese production of electrets alone is estimated to exceed 20 million units per year.


Barry
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ArtRock

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Re: Condenser Mike w/o Power Source???
« Reply #6 on: November 27, 2005, 12:51:36 am »

 Cool Cool!!! Now we may be getting somewhere. That was an interesting read, Barry! So perhaps this Grundig has permanently polarized plates? I'll see what else I can find out about that.
                   Thanks, Art
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Malcolm Boyce

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Re: Condenser Mike w/o Power Source???
« Reply #7 on: November 27, 2005, 01:10:51 pm »

Electret condenser.
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Teddy G.

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Re: Condenser Mike w/o Power Source???
« Reply #8 on: November 27, 2005, 11:36:01 pm »

What happens when you plug it in to something - like a preamp..?


TG
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ArtRock

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Re: Condenser Mike w/o Power Source???
« Reply #9 on: November 27, 2005, 11:51:34 pm »

Hey Teddy!

  As I stated in the first post, this mike works when plugged into a high impedance adapter into my board's mike pre's. Having only the two connections as illustrated has puzzled me.
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Frob

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Re: Condenser Mike w/o Power Source???
« Reply #10 on: November 27, 2005, 11:51:56 pm »

i used to have a astatic mic with almost the exact same capsule. the bace had a nine volt battery w/powersupply.

josh

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Re: Condenser Mike w/o Power Source???
« Reply #11 on: November 29, 2005, 10:01:23 am »

A two-conductor cable is all that is strictly needed for unbalanced connection to a condenser mic.  We use a three-conductor cable routinely to get a balanced interconnect.  Phantom power is present on two pins, the very two pins that carry the signal from the mic.  The third pin in this case is ground.

The picture is certainly a condenser mic of some sort.

Now you say the mic "works" when plugged into a high-impedance "adapter" and I guess I'd have to know what you mean by "adapter" and "high-impedance".  If you mean you have a connector with a 1/4" jack passively connected to an XLR plug on the other end, then it's probably allowing phantom power to flow from the console.  If you have a transformer "high-impedance adapter" (aka "passive direct box") then no DC current would flow from the console but with enough gain you may be able to hear SOMETHING.  Now if you have an active DI box or some other kind of active high-impedance input (such as the jack on a guitar amp, for example) then those circuits are typically direct-coupled to the input of the amplifier and can pass DC current through the device that you have connected to it (such as a guitar pickup ..).  In this case you'd be accidentally powering the mic with some uncontrolled or unspecified amount of power.

My guess is that you are somehow accidentally powering the mic due to the way you have it connected, either leaking some phantom power to it or otherwise leaking current from the input of the device to which it is connected, enough current to power to the mic to produce an output.  However I couldn't say for sure without more details of your setup.

ArtRock

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Re: Condenser Mike w/o Power Source???
« Reply #12 on: November 30, 2005, 12:57:36 am »

Hey Josh! We're almost neighbors!!  Cool  
I guess I should have been a bit more concise. What I have is the mike in question whose cable is terminated with a standard tip/sleeve 1/4" phone jack. This is plugged into what I have always called an impedance matching transformer adapter which looks very much like this one.  index.php/fa/1958/0/ It has a 1/4" female phone jack input and a male 3-pin XLR output. This is plugged into one of my board's microphone inputs with the phantom power turned off. It is in this setup that I say the mike "works". The output is fairly low, but not to an extreme. I am reluctant to try it directly to phantom power, as my understanding of the correct pin out connections sends one leg to XLR pins 2 & 3 (which should each be connected to one of the two mike element terminals which will then have no voltage across the element), and the other leg is connected to pin 1. I don't want to fry the element by sending 48 volts across it. Is this not what would occur, or am I mistaken?
This is where I become confused! Rolling Eyes
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josh

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Re: Condenser Mike w/o Power Source???
« Reply #13 on: November 30, 2005, 08:59:44 am »

well hmm...

makes me wonder a whole lot of things about that interconnect scheme.  If there's a transformer in there, then there should be virtualy no DC current flowing to the mic, at least not nearly enough to power it.  I'm with you, I wouldn't send it 48V until I knew it was made for it (sounds like it's not).

That's definitely a confusing situation.

Is there any kind of pre-amplifier in the mic itself?  Any electronics at all?  An electret needs power not to charge the plate (it's permanently polarized), but to power a buffer or preamplifier in the electret cartridge.  A modern electret cartridge such as those in common cheap mics (Behringer ECM8000 for example) has a little FET built into the mic that requires power to operate.  However without the FET, there is potentially some signal coming from the mic, albeit a very small amount.

So maybe this electret element you have is large and sensitive enough to produce some useful output without any buffer or preamplifier.

???

that's very odd.

I wonder if someone in Klaus's forum would have a better answer than the cheapskates over here in Harv's world.

Malcolm Boyce

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Re: Condenser Mike w/o Power Source???
« Reply #14 on: November 30, 2005, 01:48:19 pm »

josh wrote on Wed, 30 November 2005 09:59


I wonder if someone in Klaus's forum would have a better answer than the cheapskates over here in Harv's world.


OK, I guess I needed to be a little more detailed when I first said:
Malcolm Boyce wrote on Sun, 27 November 2005 14:10

Electret condenser.


The electret is a member of the condenser microphone family.  The power requirements are taken care of by a self-polarized or electret capacitor element within the mic.  The permanent charge eliminates the need for an external polarizing voltage.

http://www.google.ca/search?hl=en&q=%22electret+condense r%22&btnG=Google+Search&meta=
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josh

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Re: Condenser Mike w/o Power Source???
« Reply #15 on: November 30, 2005, 02:27:44 pm »

yes we know that but it doesn't (normally) eliminate the need for some kind of preamplification beyond just plugging it into the console.  Most modern electrets have a FET buffer at the very least.  Seems this one works without any amplification at all.  You don't see a lot of large-diaphragm electrets.
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