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Hi! From the physical size of what's displayed in the video, this looks like a quarter watt, carbon film resistor. The capacitor's voltage rating is simply a maximum expected voltage that the capacitor can handle without popping. Looking at the schematic provided, the capacitor is in the path of the +48V phantom power from the XLR (unless my layman eyes deceive me), so I'd use the expectation that about +50V could be applied to it. In electronics engineering, the rule of thumb is to double or triple the maximum expected voltage and use that for the capacitor rating to ensure safe operation. That means in this case, you'd look for a 100V electrolytic capacitor with a capacitance of 1 micro Farad (1 uF)

Could you please tell me, according to the diagram, I have to connect the 48V phantom power to the microphone's negative?​@@jefferyreber1682

hi how can i use a battery i do not understand you're instructions i am still new to the hobby

@@ruphusbau3721 Just use a AA battery. You wire it in series with the carbon button mic. Make a switch in series if you plan to keep it plugged in so it doesn't die.

did you end up making one? I'm a newbie too and had the same question regarding polarity of the capacitor. did you ever figure out the direction?

@@Mauve.Mallow I did! I found another circuit that shows the polarity direction. Search for a project called Landline by Evan Cook, you'll find a page with documentation for a near identical circuit (minus the switch) that shows how to orient the capacitor. Hope this helps!

On off on. The two end positions switch between the two microphones, and the middle position does nothing.

@@RyanMobitz Is there a difference between on-off-on and on-on switches? Or might I be able to get away with using an on-on dpdt switch?

@@zamajamba4455 yeah, should work fine

​@@RyanMobitzCould you please tell me, according to the diagram, I have to connect the 48V phantom power to the microphone's negative?

I got mine on eBay. Was the easiest place I could find like, a pack of five of them for $10 instead of hundreds of them for hundreds of dollars.

Mics and speakers work on the same principle, just in reverse. Mics take sound and converts it to voltage, and speakers take voltage and converts it to sound. As such, you can use a speaker to capture sound if you plug it into an input, rather than an output. Some studio engineers, for example, will use a fairly large speaker (10", say) to mic low pitched sources, like kick drums. Here's the folks at Electrical Audio explaining how to do just that - czcams.com/video/7ryJanXTMjI/video.html

The diagram has a single transformer with 6 pins, 3 on each side. Some transformers have 6 pins total, some just have 4 total and don't have one in the middle. If you're using a 4 pin transformer, or the middle pin on your 6 pin transformer isn't working (like mine weren't) then you can connect that wire going to the middle pin in the diagram to EITHER of the side pins in the same side, and have two wires soldered to a single pin. If you pause the video at 1:54 you can see me doing this, and that the middle pin actually completely broke off on one side.

Run it through a D.I with ground lift?

The earpiece, yes. Just don't do anything with the ground and it won't need phantom power.

@@RyanMobitz one last doubt, for this you used a pcb, is it necessary? or just following your diagram

@@by.daekeryyy Just follow the diagram, you can solder wires to wires and it should work no problem.

The diagram has a single transformer with 6 pins, 3 on each side. Some transformers have 6 pins total, some just have 4 total and don't have one in the middle. If you're using a 4 pin transformer, or the middle pin on your 6 pin transformer isn't working (like mine weren't) then you can connect that wire going to the middle pin in the diagram to EITHER of the side pins in the same side, and have two wires soldered to a single pin. If you pause the video at 1:54 you can see me doing this, and that the middle pin actually completely broke off on one side.

@@RyanMobitz I see, it really helps a lot, thx!!!

Yup! At some point in history these phones just started using the same dynamic mic in both the earpiece and the mouthpiece, so "newer" old phones are likely to have a dynamic mic in both.

@@RyanMobitz How can I differentiate between carbon and dynamic microphones?

@@SNTFRR if you shake it and hear what sounds like a saltshaker its a carbon mic

lmaaao thought so too haha

That wasn't me, I've only got this one.

@@RyanMobitz Thanks for the reply! I was able to figure out the pins and get it done. Do you have any other cool DIY projects like this you've done?

@@AAWSAPRocky I haven't, well at least not filmed I actually bought my soldering iron FOR this project 😅 there's a channel called bleepboxes youight enjoy though!

@@RyanMobitz looks cool! Thanks for the recommendation!

Your best option for that would probably be just 2 separate circuits with 2 XLR ports and then you can mix the inputs in your daw.

Absolutely, yes

That might be bc of the assumption of 48V phantom power from an audio interface, cant be for sure until i build it myself tho

@@danielflecha4154 ^^^

I got them on eBay. If you look up 600:600 audio transformer you'll find a bunch of 5-10 piece packs for <$10. The schematic shows a 3 pin transformer, but most of the packs on eBay only have 2 pin transformers. The center 3rd pin on the pack I got didn't actually connect to anything, and it took me FOREVER to figure that out. I ended up just connecting that wire with the resistor to one of the two side pins and it worked fine. So I think any of those packs, even with 2 pins, should work fine. Your choice will probably be made on price and shipping time as most of them are coming from China. For completions sake though, these are the exact ones I used. www.ebay.com/itm/252429737989

@@RyanMobitz thank you! very helpful

Hello! I'm trying to build this circuit, but I couldn't find a center tap transformer, how do I connect it with just two pins? Will it work anyway?

@@giacomobrondino6561 did u try that out

@@mv7853 Yes, it works. it has a lot of noise but probably it's normal for a carbon mic...

I don't know what the brand was, but I do know the phone it belonged to had buttons. It was an old hospital phone. Given that you're ripping everything out except the carbon mic and the speaker coil, I don't think newer phones would make it more complicated to build, but they may just not have the carbon button mic in the mouthpiece. At some point in time, handsets started replacing the carbon mic with a dynamic mic, similar to and usually an exact copy of, what was in the earpiece. So if you're just looking for the dynamic piece any phone should do. If you're after the carbon, buying in person and checking the innards first might be the safest bet.

I just played the original recordings back through my monitors, and re-recorded them with the phone. The vocals were post-production recordings from a cover I did, and the drums were made with a drum machine.

@@RyanMobitz thanks. Makes sense. I have a 1969 ITT phone I’m using for this and other mods.

Calling a video a VDO is never going to catch on lmao

I almost put a pot in the middle but didn't end up having space in the housing for it. This was the plan: czcams.com/video/Ch9w5JtbZSc/video.html There are builds where people just use one mic and then put the filter setup where I put the switch, but I opted for the 2 different mics and then post-processing vs wiring in a filter.

@@RyanMobitz Cool! I'll try it! thank you for replying!

Another cool idea! I thought about maybe using 2 XLR cables and wiring them separately for stereo recording. Some newer phones have the same speaker in the earpiece and the mouthpiece instead of using a carbon mic.

@@RyanMobitz wiring them in series is easy though, and will have a humbucker effect (and I believe no phase issues). but they will be in mono

@@sloppy_hand but then you pan one signal hard left and the other hard right to get the stereo sound

@@RyanMobitz I don't know if you can do it with them wired in series... can you? isn't it one speaker's signal goin' through the other speaker before the output?

@@sloppy_hand No it wouldn't work if they were in series, only if you wired them as two separate mics for two separate inputs.