Grundig GDM 313 Microphone

[razabri]

Well, since no one is interested in helping out with this one on any of those cool, gearslutzy and so very sophisticated diy audio forums, I might as well try it here

So, I got this mic at a flea market for about $3 and it's fairly common in my region and it pops out for sale here and there...

It came with a box and it's kind of likable, as far as those old tech thingies go, but the output was very faint. I thought maybe it's suppose to be like that so I tried it with a preamp and it's working ok.

But then I thought, maybe there's something wrong in there and suddenly I was struck with a genius idea to take it apart and have a look inside. That's when I managed to disconnect the capsule.

So, I was wondering if anyone can assume how this supposed to be wired, regarding the transformer and all?

I have some pics, and the transformer has three wires, red, green and white. Green goes with the yellow one from the cable, red goes with blue and white goes with what I assume is ground. I'm not sure where to solder capsule's wires, as there's no clear trace where they were.

I'we drawn a simple diagram as well...









Thanks!!!

[anotherjim]

I'd assume its a dynamic and the transformer gives impedance matching choices. Does the capsule do decent output on its own? Old capsules usually have rotted diaphragms in my experience of them.

[razabri]

I'd assume its a dynamic and the transformer gives impedance matching choices. Does the capsule do decent output on its own? Old capsules usually have rotted diaphragms in my experience of them.

Yeah, it's an old dynamic thingy, with a heavy metal head and plastic handle and it does say, at the radiomuseum site that it has the impedance matching integrated... It does have an ok output by itself, the capsule, but I would want to try and get its original wiring right and then decide if I'd just bypass the transformer.

[Kipper4]

Reminds me of the mics that commonly came packaged with cassette tape recorders in the last image.
Reminds me of taping the top40 on Sundays. UK.
You would set the mic on its little plastic stand in front of the transistor radios speaker and record it,listen to it all week until the new top40.
C90 was the longest tape time wise that didn't distort too much with repeated recording and playback.
IIRC.
TDK C90 where a fave tape.



What type of output jack has it got? 5 pin din?

Some models even had a tape pause switch built in.

[iainpunk]

i dislike most DIY audio forums, they have a bad atmosphere, unlike this forum 
but gearslutz... well, i don't often use this word but here it is, i hate the community on there. have had some bad experience with stubborn, annoying and self righteous a$$h0les who threatened me because i dared to claim that changing tubes for the same type but another brand does not make a difference at all. it has been scientifically proven. but you can't get to those religious nuts over on gearslutz.

however,
please measure the resistances for us! there should be one wire with nearly 0 ohm to the bare wire (let call that one N), and then the other two, lts call them S1 and S2, should have a resistance to N, lets call that Rt, Rt from both should be similar, and the resistance between S1 and S2 should be 2xRt. connect the capsule N and one of the S wires

cheers, Iain

[razabri]

Reminds me of the mics that commonly came packaged with cassette tape recorders in the last image.
Reminds me of taping the top40 on Sundays. UK.
You would set the mic on its little plastic stand in front of the transistor radios speaker and record it,listen to it all week until the new top40.
C90 was the longest tape time wise that didn't distort too much with repeated recording and playback.
IIRC.
TDK C90 where a fave tape.



What type of output jack has it got? 5 pin din?

Some models even had a tape pause switch built in.

Thanks for the reply! Yes, we had something similar when I was a kid, and I remember the 5 pin mic insert on our stereo (Neckelman?) and who knows where the mic ended up... And the tapes, TDK was the brand when I was a teenager, we would listen to recorded stuff till they fall apart

Yeah, this one also has a 5 pin jack, but it came with an original adapter to 6.3 mono, so I've been able to test it without problem.

[iainpunk]

i'm not really from the tape era but when i was 14, i bought an old walkman specifically to listen all day, for the whole summer to one tape my dad has: the Jesus and Mary Chain - Psycho Candy
i literally only liked one tape in our collection, and i couldn't listen to it all day on the living room stereo set because it drove my brother mad.

cheers, Iain

[razabri]

i dislike most DIY audio forums, they have a bad atmosphere, unlike this forum 
but gearslutz... well, i don't often use this word but here it is, i hate the community on there. have had some bad experience with stubborn, annoying and self righteous a$$h0les who threatened me because i dared to claim that changing tubes for the same type but another brand does not make a difference at all. it has been scientifically proven. but you can't get to those religious nuts over on gearslutz.

however,
please measure the resistances for us! there should be one wire with nearly 0 ohm to the bare wire (let call that one N), and then the other two, lts call them S1 and S2, should have a resistance to N, lets call that Rt, Rt from both should be similar, and the resistance between S1 and S2 should be 2xRt. connect the capsule N and one of the S wires

cheers, Iain

Thank you for the reply and yes, I got that kind of an impression at other forums, but I wanted try not to bother folks over here, since dudes already helped me so much before with figuring things out, and this is an off topic thing... Guess I should be glad that no one replied to my posts 

About the resistances... Well, as embarrassing it is, I have to say that I got no multimeter  Yet. Solder iron and solder, sure, even that thing with a magnifying glass and little clamps. Guess I'll have to come up with one to make this work properly.

But hey, I did connect the capsule to the S1 and the one that's drawn white and it actually has transparent insulation and I got a decent output like so. The only thing is that I don't know what's happening in this circuit, am I bypassing the transformer or not? Hope to get it figured out...

[iainpunk]

i bet that you could get a digital multimeter from the dollar store, that's quite adequate for most pedal building anyways, better a cheap one than none at all.
i'd say a multimeter, event the cheap ones, are an essential tool

try connecting it over the red and white transformer cables, that's my best guess.
if that doesn't work try red and green, and then green and white... its not that hard to solder and desolder the wires to try it out what works best

cheers, Iain

[razabri]

You're right, I'll try and find something usable and get back with the values. Thanks!

[iainpunk]

but I wanted try not to bother folks over here, since dudes already helped me so much before with figuring things out, and this is an off topic thing..

were all friendly here, most of us probably don't mind helping you with less pedal related topics as well.

its really magical how this forum keeps friendly without heavy moderation, that doesn't happen often... most unmoderated places on the internet become really aggressive, troll-prone, hostile and right wing or massive p0rn dumps, just like 4chan's /POL/ and /B/. and heavily moderated places become anti free speech stalinist nightmares, like facebook and/or twitter.

cheers, Iain

[razabri]

Yes, I've noticed it too - this one's great and it's populated with people who wouldn't mind getting into stuff, like solving some kind of circuit mystery or something. I've had a situation recently with an unknown reverb driver circuit that I had almost no hope in getting to work, but guys here were great and solved it, with great feedback.

And my impression is that other forums are not so friendly, but I have to say that over there, at diyaudio.com someone did reach out and sent a schematic that could be helpful in this case.

https://imgur.com/a/nWjJeBr    (for some reason adding image option doesn't work now)

The transformer colors do match, but I'm still unsure what to do, where to solder capsule's two wires...

[iainpunk]

i recommend just trying and retrying.
an educated guess is the red and white wire of the transformer, or green and white, as the red and green are on the same side it gives me the impression that they are the outermost connections, and the white one is the middle connection. you want to amplify the incoming signal so putting the capsule over one outer and the middle, it doubles the signal on the other outer connection.

cheers, Iain

[razabri]

i recommend just trying and retrying.
an educated guess is the red and white wire of the transformer, or green and white, as the red and green are on the same side it gives me the impression that they are the outermost connections, and the white one is the middle connection. you want to amplify the incoming signal so putting the capsule over one outer and the middle, it doubles the signal on the other outer connection.

cheers, Iain

Yeah, I was going for that and at the moment have connected the thing the way I said earlier, but I do want to try and find the best combination. I'm not really sure if I understand your explanation - what would outermost and middle connections refer to? If I understood right I should go from the capsule to one outer connection of the transformer and the middle (I guess it's ground) and then the left connections from the transformer is the one with the signal and goes with the ground to the mic cable and connector... 

[iainpunk]

these colours is what i expect them to be, but tis only an educated guess. but i don't think it really matters to much anyways, there will be usable output anyway you place the capsule, some louder than others, but still usable.


cheers, Iain

[razabri]

Thanks! Yes, I believe I have connected it now the way it's usable - here's another amateur drawing of the current setting.




The thing is, that I've noticed that there's a small circuit drawing on the adapter jack from 3 pin old jack to 6.3mm mono and as I see it, there's a connection made between blue and transparent wire and that's all connected with the shielding as well. It leaves only yellow one with a signal. The use of different impedance was possible probably with a specific tape recorder that could switch between the two pins, sending different signals.

My setting right now is ok - I have good, strong signal, but as I see it, the transformator has no purpose here and it seems to me that it's bypassed, as I'm using only yellow wire directly this way and the other conection just becomes ground... I don't know, really...

[iainpunk]

if you are satisfied with the mono 1/4" jack plug, you could indeed leave out the transformer
i also recommend getting a new 1/4" jack plug and solder that to the wire instead of the 3pin that's currently there.

cheers, Iain