Carbon Microphones

[abbey road d enfer]

The interesting thing is that diaphragm has to be spaced away from the magnet correctly or it will stick and won't vibrate. Very much like a LDC.

That's correct. I remember there were washers that allowed changing the sensitivity by making the diaphragm more or less close to the magnet, until it stuck.

 

[Ricardus]

I built the circuit comprised of 3 10k resistors, and 2 capacitors, and it was really hot and sounded like trash in an especially trashy way that was beyond what I was going for. I just ran across the following link yesterday, that looks like a 48v Phantom power version of the 600:600 transformer circuit.
The maker also put in a flip switch to switch between the carbon button mic and the ear-piece as a dynamic mic.
https://www.pro-tools-expert.com/production-expert-1/use-an-old-phone-handset-to-produce-a-lo-fi-mic
Having a center tap transformer should improve the sound a great deal, just from being able to balance it. The builder has sound comparisons in the video, and I like the old-timey sound of the carbon button that sounds nothing like what I was getting with the transformerless circuit. I just ordered some 600:600 center tap transformers, and I'm going to ditch the flip switch and see if I can fit all the electronics into the handset to use the ear piece as a monitor and carbon mic as a mic and plug into my audio interface for zoom calls.

It's been a while since I've tried building a PCB in KiCAD, but I figure it should be a pretty simple board.

Is that schematic right? It says there's +48 on pin 1.

I was going to mod the other circuit with the 10K resistors with a transformer. I'm still going to try.

I love the trashiness of the way that one sounds.

 

[abbey road d enfer]

Is that schematic right? It says there's +48 on pin 1.

Apart from this gross mistake, it seems to be correct.

 

[revmonkey]

I built the transformer version of the circuit I posted earlier in this thread. I knew going into this that I didn't know what I was doing, but I sure hate being proved right about such things. It's really hot. I'm not sure if there is some impedance matching issue, other part selection issues, or I just need to learn how to build a pad into the signal path, but it's too loud to be very useful for any moderately loud sources. If someone with actual electrical engineering knowledge can easily tell where I went wrong, I would love some advice...or a link to a good description of how I might add a pad to this, if that seems like the best solution. Anyway, here is the circuit as I have built it, and the list of individual components I used.




R1: 493-11354-1-ND
PART: 493-11354-1-ND
MFG : Nichicon (VA) / UPW1H010MDD1TD
DESC: CAP ALUM 1UF 20% 50V RADIAL

C1:
PART: A131630CT-ND
MFG : TE Connectivity Passive Product (VA) / RR02J6K8TB
DESC: RES 6.8K OHM 5% 2W AXIAL

T1:
PART: 3475-AEI24-4410-ND
MFG : Allied Components International / AEI24-4410
DESC: EI24 Audio Transformer

Carbon1: OZ-01 Standard Transmitter

I'm not sure if I just found the issue, or just "an issue", but in making sure I'm including proper links, I think maybe my transmitter isn't actually a Carbon button transmitter. Under "Type" it's described as "Carbon-compatible Electret" which probably means...not a Carbon button.

I just ordered this one, to see if it behaves differently. T-1

If any other issue pops out and says "HERE I AM", I would love a set of eyes connected to a more educated brain.

 

[abbey road d enfer]

Carbon mics were used in POTS without any amplification, they were so hot they could "talk" over miles and miles of landlines.
You just need to build a "U" attenuator between the xfmr secondary and pins 2 & 3 of the XLR.

 

[Ricardus]

I built the transformer version of the circuit I posted earlier in this thread. I knew going into this that I didn't know what I was doing, but I sure hate being proved right about such things. It's really hot. I'm not sure if there is some impedance matching issue, other part selection issues, or I just need to learn how to build a pad into the signal path, but it's too loud to be very useful for any moderately loud sources. If someone with actual electrical engineering knowledge can easily tell where I went wrong, I would love some advice...or a link to a good description of how I might add a pad to this, if that seems like the best solution. Anyway, here is the circuit as I have built it, and the list of individual components I used.


View attachment 92804

R1: 493-11354-1-ND
PART: 493-11354-1-ND
MFG : Nichicon (VA) / UPW1H010MDD1TD
DESC: CAP ALUM 1UF 20% 50V RADIAL

C1:
PART: A131630CT-ND
MFG : TE Connectivity Passive Product (VA) / RR02J6K8TB
DESC: RES 6.8K OHM 5% 2W AXIAL

T1:
PART: 3475-AEI24-4410-ND
MFG : Allied Components International / AEI24-4410
DESC: EI24 Audio Transformer

Carbon1: OZ-01 Standard Transmitter

I'm not sure if I just found the issue, or just "an issue", but in making sure I'm including proper links, I think maybe my transmitter isn't actually a Carbon button transmitter. Under "Type" it's described as "Carbon-compatible Electret" which probably means...not a Carbon button.

I just ordered this one, to see if it behaves differently. T-1

If any other issue pops out and says "HERE I AM", I would love a set of eyes connected to a more educated brain.

I had to do a small Mouser order to finish my ML12, so I added some caps and transformers to fool around with this design a bit more.

Curious to see the progress on your design.

 

[abbey road d enfer]

I'm not sure if I just found the issue, or just "an issue", but in making sure I'm including proper links, I think maybe my transmitter isn't actually a Carbon button transmitter. Under "Type" it's described as "Carbon-compatible Electret" which probably means...not a Carbon button.

I'm afraid that's the case. It's an electret capsule housed in an old-style standard mic.

 

[revmonkey]

I had to do a small Mouser order to finish my ML12, so I added some caps and transformers to fool around with this design a bit more.

Curious to see the progress on your design.

It's coming along. I have it working on a breadboard. I have the resistor placements for the U-pad attenuator, but haven't yet figured out the K-value for actual resistor values.
I have been working on a PCB in Kicad,. I got side-tracked when my 3D printer arrived and have been revising a housing for it based on the 1940s/50s Turner 33x, which looks kind of cool. Yesterday, I printed the retaining clip for the capsule and assembled the grill, capsule, and retaining clip and hooked it up to the breadboard. Yup...still works. Still sounds like hot garbage. I still need to add PCB mounts to the main housing, but should finish the PCB design first.

When I'm done, it's going to look really nice, and, I assume, create reasonable approximations of old vaudeville recordings.

 

[Ricardus]

It's coming along. I have it working on a breadboard. I have the resistor placements for the U-pad attenuator, but haven't yet figured out the K-value for actual resistor values.
I have been working on a PCB in Kicad,. I got side-tracked when my 3D printer arrived and have been revising a housing for it based on the 1940s/50s Turner 33x, which looks kind of cool. Yesterday, I printed the retaining clip for the capsule and assembled the grill, capsule, and retaining clip and hooked it up to the breadboard. Yup...still works. Still sounds like hot garbage. I still need to add PCB mounts to the main housing, but should finish the PCB design first.

When I'm done, it's going to look really nice, and, I assume, create reasonable approximations of old vaudeville recordings.

Looks great.

I have some ideas for making vintage looking art-deco-ish housings also.

 

[revmonkey]

I also bought a broken Turner SR-90R. It has more of a deco vibe than the 33x.

 

[Tubetec]

Hot Garbage , ahahah
that little transformer is probably squarewaving due to core saturation .

 

[revmonkey]

Hot Garbage , ahahah
that little transformer is probably squarewaving due to core saturation .

As a self-aware idiot with more ambition than is reasonable, what's the solution to this? Resistors on the primary coil side? Get a transformer with fewer winds? I'm out of my depth here.

 

[Tubetec]

Should be easy enough to figure out a resistive attenuator before the transformer primary for higher level sources , like amps and drum kits , simply switch it out when your dealing with voice or lower level sound sources.

 

[Tubetec]

Ambition is the building block , the foundation of all things good .

 

[Harvey Birdman]

Hi there, can you tell me what type of paint finish you used on the old Tuner carbon mic. Thanks