Building a Lo-Fi Mic From an Old Phone

Carbon Mic Circuit Source: www.logosfoundation.org/g_tex...
Guitar Sample: Tash Wolf - An Afternoon in April

[@xanataph]

if you don't have a transformer you can use a nine volt battery to power the carbon mike. Which also means you can feed it into inputs that don't have phantom power. You make a circuit with the battery connected to the mike through a resistor and then take the audio out through the capacitor and ground.

[@ruphusbau3721]

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

[@olin9310]

@@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.

[@TheSame92]

This has been going around in my head recently. Now that I see it in practice I will definitely try it out! Great video Ryan!

[@johnhardig9754]

Wow best video on this subject! and the sound examples were so helpful.

[@WJCTechyman]

It's very neat. I would have made it so you had two XLR3 ends coming out of it, so if you wanted to, you could mix them together on your mixing console. I don't know how useful it would be for voice but for some instruments like drums you would have that feature.

[@gogo6508]

Thank you for that, i'd love some other building tutorials in the futur

[@JAROCHELOcesarcastro]

What a great video, project, etc. I want to make one now!!!

[@Runneround]

done it, works a charm! for all you wondering, yes you can use the - um - spirally wire. i set it up so that the xlr plug is in the housing of the old telephone body. if you don't know what to do with the ground wire from the xlr cable, you can connect it to the negative (3) wire, of said xlr cable. one more thing to keep in mind, not all phones have carbon mics, mine had a dynamic speaker and a dynamic mic...

[@RyanMobitz]

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.

[@SNTFRR]

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

[@benbeach4425]

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

[@DJTabooMixTypeBeat]

After watching your VDO, I just went out to the thrift store to get those rotary phones. Thanks for this VDO.

[@Leo9ine]

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

[@MIHAO]

great stuff, need to make one for myself :)

[@ACURAOCULTA]

Very good

[@robertsimpson5801]

Very cool video! I hate to even ask, because you did such a great job with this video, but is there a way to build one of these so that there are two outputs; one for the carbon mic and one for the other microphone? Essentially, having two separate circuits in the same handset, with one mic on each end? If so, would you mind showing us how?

[@ToddTH]

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[@crossprieto7687]

Could someone explain using the PCB, Is it just to connect the audio transformer to both mics and the switch?

[@LeeRedfieldmusic]

What brand did you use for this build? I suspect some will not be this easy. Do you think later models that were button instead of rotary will have the same setup inside?

[@RyanMobitz]

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.

[@RambunctiousFlan]

Thanks a ton for this vid Ryan! I'm currently in the process of getting parts for this project, and as I'm a bit of a novice when it comes to the electrical engineering side of audio work, I wanted to ask what type of capacitor you used. The lack of polarization denoted on the diagram would make me think ceramic, but (and my eyes could very well be deceiving me) the capacitor in the video looks more like an electrolytic capacitor to me, so I was a bit confused. Also, should I have any worry about the direction of the transformer, or will that not matter since it's 1:1? I appreciate any clarification! I just really want to make sure I go about this project correctly 😅 Thank you again!

[@Mauve.Mallow]

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?

[@RambunctiousFlan]

@@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!

[@TheAustrianBoys]

Can you also reuse the coil telephone cable as for a example an instrument cable if you solder it newly?

[@Leo9ine]

Absolutely, yes

[@improziv]

Great project. I’m working on a similar thing. Wondering how you got all three recording sources captured? Are they all re-amped through a speaker? Separate performances?

[@RyanMobitz]

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.

[@improziv]

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

[@miketheknife813]

I want to do this, but I want to use the cord that comes with the phone, but I don't know how to do any of this fancy stuff, or how to get the stuff either

[@JRut99]

Hey can you explain the PCB part? I’ve never soldered PCB before and it confuses the hell out of me

[@boscorner]

I actually found an xlr cable f rom an old power supply in my basement so I'm gonna search for an old phone and try this out (yea apparently XLR was used in power supplies as well as audio)

[@user-bx2vt7ki7j]

Would it be possible to wire the transformer before the switch to protect the whole circuit from 48v power ? Making the transformer inpedance and power bridging from the plug to the output of the switch ? Also, how's the gain on your pre-amp to run this mic ? Would it be possible to used a transformer with a better ratio to have a better output on the XLR ? Or am I missing something ? Thanks alot !

[@keeganlarose]

Would it be possible to use a 3 way switch, with the third option being both mics at the same time?

[@RyanMobitz]

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.

[@brianzditowski6431]

Awesome build, mate! what would you recomend if I want to put a tone pot? cheers!

[@RyanMobitz]

I almost put a pot in the middle but didn't end up having space in the housing for it. This was the plan: kzbin.info/www/bejne/eZmcqGiAqceNicU 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.

[@brianzditowski6431]

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

[@zischtwieapfelsaft1]

the output of the carbon mic is a bit hot for me, any chance it got smthg to do with faulty wiring, like capacitor backwards or smthg?

[@Bleats_Sinodai]

Are you sure your wiring is correct? You're showing 48+ volts on your ground wire.

[@danielflecha4154]

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

[@RyanMobitz]

@@danielflecha4154 ^^^

[@Ducklimp]

Which way does the capacitor go?

[@bryanchew4355]

Hi I have a problem in building this... Is the 600:600 transformer from the diagram actually showing 6 pin or 3 pin? And can I connect 2 wire into a pin? Sorry for asking as I'm still learning it myself and I couldn't figure it out...

[@RyanMobitz]

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.

[@bryanchew4355]

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

[@sloppy_hand]

would be cool if you could use them in parallel... and as an overhead mic for drums. what do you think?

[@RyanMobitz]

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.

[@sloppy_hand]

@@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

[@RyanMobitz]

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

[@sloppy_hand]

@@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?

[@RyanMobitz]

@@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.

[@calyx0]

hello! i did this and i get a lot of ground noise, how can i fix that?

[@JRut99]

Run it through a D.I with ground lift?

[@Dcurucci]

Can someone please explain how the transformer in the schematic has 6 contact points yet the physical transformer has 4?

[@RyanMobitz]

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.

[@justingammella3786]

How much to have you build one for me and ship it out? I am very serious.

[@ItsMurfCat]

Are the 6.8 resistors 1/4 watt or half watt or does it not matter what wattage?

[@AAWSAPRocky]

Did you take down some of your videos? I was looking for one earlier and couldn’t find it about CB radio mic to XLR

[@RyanMobitz]

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

[@AAWSAPRocky]

@@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?

[@RyanMobitz]

@@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!

[@AAWSAPRocky]

@@RyanMobitz looks cool! Thanks for the recommendation!

[@zackpassman]

this is a build i am planning. can you point me to the transformer you used? Thanks!

[@RyanMobitz]

I got them on eBay. If you look up 600:600 audio transformer you'll find a bunch of 5-10 piece packs for

[@zackpassman]

@@RyanMobitz thank you! very helpful

[@giacomobrondino6561]

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?

[@mv7853]

@@giacomobrondino6561 did u try that out

[@giacomobrondino6561]

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

[@quagsm]

hey dude, where do i can get the transformer?

[@RyanMobitz]

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.

[@ruphusbau3721]

how many watts is the resistor and how many volts the capacitor??

[@jefferyreber1682]

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)

[@by.daekeryyy]

can i solder de xlr cable directly to the mic of the phone?

[@RyanMobitz]

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

[@by.daekeryyy]

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

[@RyanMobitz]

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

[@Channel__T]

How is the speaker also a mic?

[@navidamlani1616]

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 - kzbin.info/www/bejne/baPce5SkjbmAoKs

[@zamajamba4455]

Is the DPDT switch ON-ON-ON or is it an ON-OFF-ON switch?

[@RyanMobitz]

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

[@zamajamba4455]

@@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?

[@RyanMobitz]

@@zamajamba4455 yeah, should work fine

[@navidamlani1616]

so...could you just use parts scavenged out of the body of the phone? Assuming the parts are of the appropriate values, of course...

[@toxic1428]

e

[@unfree.radical]

I'm mostly interested in capturing both voices to mic a guitar amp. I think the spacing will be about right to get cone and rim tone. With a handset that has two dynamics I thought to use a guitar switch so I can have A, AB, B options. With a handset that has dynamic/carbon would this still be possible or would it cause a fault summing the passive and active signals? I suppose if they can't be directly summed, one could run a dual cable, its just not as neat of a solution.