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[Onkel Kompost]

Hi to all of you.
Here is a question for those of you in the know when it comes to microphones.

I recently purchased a Grundig GKM17 microphone (anno 1960), and is currently in the process of finding out things about it so that I may use this mic for my own recording purposes.

According to this http://www.xs4all.nl/~odemar/microphones/eur-mics.htm site the one thing that the Grundig in question had going for itself was that it was a condensor microphone, and was used a lot for portable recording.

Now, what followed is what worried me, and i quote: "Being a condensor microphone, it required a 100 V polarisation (supplied by some model Grundig tape recorders).".

And here is my question:

If I get hold of an adapter to this particular mic, do you think it'll handle being used, or is the polarisation a problem? I hope you gentlemen can answer my question. I am not exactly dying to kill off either a mic amplifier or my mic inputs, so this is the reason for me asking.

Thanks in advance

[Level]

The base of that mic is a "dead ringer" for the one on my Robbins & Myers antique electric fan!

It would seem you need to have a power supply contructed. Perhaps one with less voltage would energize the capsule. Klaus would know!
\

[ArtRock]

Onkel,

  Welcome! It's interesting that I just posted a VERY similar thread on Harvey Gerst's forum. I have a fairly large vintage mike collection which includes a GCM3 and have been wondering the same thing. Here is the gist of my posts on Harvey's forum...

8< ----------------------------------------------------------->8
I've been wondering about this for awhile...  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.


8< ----------------------------------------------------------->8

  Then, Barry Hufker responded with:

8< ----------------------------------------------------------->8
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.
8< ----------------------------------------------------------->8

  I was reluctant to post my question in Klaus's forum as it was designated as "High-End Microphones" which I unfortunately do not have the means to aquire. I'm sure he will let us know if we're out of bounds here, and, if so, I apologize. Onkel, I would appreciate very much your sharing ANY info on this microphone with me, and I would be pleased to do the same.

                Thanks, Arthur McKnight

[Grundigcollector]

Hello Grundig collectors,
The GKM17 and the GCM3 are the same microphones.
This microphone has a oval feet and has clinch.
The GKM7 has a round feet and a emblem of Grundig.
See picture.
1e=7 2e=7 3e=17 4e=17 bleu 5e=17 6e 7

A collector from the Netherlands

[rodabod]

Do you know much about the small white Grundig ribbon microphone, model GBM...

I have one and think it sounds quite good. I have heard it was made by Beyer, but I am a little dubious.

[Grundigcollector]

Hello,
Do you mean the GBM 125.
That microphone is original from Sennheiser.
At this moment i have no picture. Sorry.

Alard.

[rodabod]

So the GBM125 was made by Sennheiser!?

I never thought that Sennheiser would have made a ribbon microphone.

It sounds quite good on electric guitar. I can't work out how to open it up though? Do you know?

Roddy

[g8zck]

Long time ago this thread but did you get the grundig mike working.I have 2 here and have them modified to work.They are very sensitive but the response falls off at the higher frequencies.
G8zck.

[Santiagoacr]

I just got a GCM3 at a carboot sale but it does not work when plugged into a regular microphone connection (its 3-pin din into my small tuchel to XLR adaptor).

Does anyone have a method for powering it (if necessary) or any adaptor for using it otherwise?

Regards,

Santiago

[simolino]

as said this grundig needs 100V polarisation, the grundig equipment that was designed for provided this voltage,they also had a preamp circuit to boost its output.
any way as stand alone it will not work without a power supply,
Just for fun you can solder an XLR (unbalanced) at cable end to test it on a 48V supply , it will work..well kind of but with a very low output and much hum (unbalanced remember)

@ Roddy
The GBM125 was a Bayer made mic, Sennheiser never made any Ribbons (I know   )
just think of it, if you need a ribbon mic would you go to a reputable ribbon maker or to someone else? and would sennheiser tool up just for one grundig ribbon model only??

[rodabod]

simolino wrote on Tue, 20 May 2008 18:02

@ Roddy The GBM125 was a Bayer made mic, Sennheiser never made any Ribbons (I know   ) just think of it, if you need a ribbon mic would you go to a reputable ribbon maker or to someone else? and would sennheiser tool up just for one grundig ribbon model only??

I thought so. The motor is the same as another Beyer ribbon mic. However, the build quality is not as good and I'm not sure if the transformer was the same model. Build quality / tolerances are quite important for ribbon motors.

[Santiagoacr]

Thanks, simolino.

I may give that a go.

I got the mic for free and I am intrigued by the idea of a large diaphragm 50-15000 Hz crappy old condenser.

I was intrigued by G8zck's comment about having these mics modified so that it would work. I suppose he meant so that they would work with 48V phantom power.

I have PM'd him but he has not replied, he does not seem to be around anymore.

Santiago

[kifkif]

The mic is rated at 2.5mV output (without needing the usual pre-amp boost) - way higher than the comparable moving coil mics Grundig produced at the time. This was apparently achieved by the HUGE 70mm diaphragm.

Pinout for a GCM mic with a 3 pin DIN plug:
the signal is on pin 1 and supply voltage on pin 3.

Pin 2 is normally ground or screen, i don't know exactly what this should be connected to. But, as long as that whopping supply voltage is not touching it, experimentation would be par for the course. Caution advised, obviously!

It is not an electret condenser, and requires a supply voltage. Originally 100v. Apparently 48v should work.
Purists can apparently incorporate a "voltage doubler" on a 48v phantom supply (Caution again!), OR, it's said, there are designs online for a 100v supply, OR, as stated above, most of the oldest (1950's) Grundig valve tape recorders are compatible and put out that 100v supply, on pin 3.
The compatible Grundig models are:
700L, 700C, 500L MKI/II,
TK5, TK7, TK8, TK12, TK15, TK16, TK20, TK24, TK25, TK30, TK35, TK55, TK60 (Stereo), TK820, TK830-3D, TK919
TM20, TM60
TR3.

As it puts out 2.5mV it does not require the "pre" pre-amplifier that other condensers usually have built-in.
To use it with the usual low impedance inputs on pro and semi pro gear, it needs a high to low impedance conversion. An audio transformer of appropriate spec (try about 100:1?) is probably best for this job. Converting the unbalanced signal to balanced may also be advisable, either electronically, or with another transformer. (not sure how common transformers which do both jobs at once, are - but may be best solution).

Those Grundig models can be found dirt cheap, and if the amp parts are working, a (valve-amplified) monitor signal output and/or a low-wattage low-impedance speaker output (easily adaptable to line level) can be taken from the machine.

Disclaimer: the above post is meant for entertainment only!
Working with voltages can be dangerous, make sure you know what you're doing first, any actions are at your own risk!

Good luck!