Dynamic Microphone switch wiring

[amanisdude]

Hi guys!

I have either an incredibly dumb or an extraordinarily sophisticated question for this forum. (You can decide which it is. )

I have a dynamic mic that came with an old computer that connects via a mono 3.5mm TS plug. The microphone had a bad cable, so I decided to take it apart and have a look. Unfortunately, when I removed the bottom of the microphone (where the cable enters microphone body), I pulled too hard and ripped the wires out from whatever they were connected to inside the mic.

However, I pressed on and found that the actual actual microphone part at the top (found in that metal mesh dome thingy, whatever that's called) had two wires coming from it (yellow and white), and both wires are soldered to the SPDT ON/OFF slide switch on the side, the yellow to two adjacent pins, and the white to the third pin.

Now, there is no evidence for how the wires in the cord were actually connected to the switch. (The cord contains a red signal wire and a grounding shield twisted into a ground wire.) Are there any mic wiring experts here who happen to know where I would solder those wires? I would be eternally grateful for any help!


‒amanisdude
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[PRHunt]

Mmm. I have what may be an incredibly dumb question.

Is the mic worth fixing?

You could work out the connections on the switch using a continuity tester or ohm meter. Otherwise hard to say without seeing.

Paul

 

[amanisdude]

Haha, it is totally worth fixing. Short of shelling out some big $ (which I don't have much of at the moment), it's the best microphone I have.

Here are some pix that might clarify things.


This is the actual microphone inside the mic chassis along with the SPDT on/off switch.


A close-up of the switch.


Where the switch was located on the body.


Here's the cord that I ripped out of the body.


This is how the hollowed-out mic body looks.


And finally, all the components in assembly order.

I hope these pictures are helpful. If there is any other angle or part that I should photograph, please let me know. Thanks for any help!


‒amanisdude
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[PRHunt]

OK, can you get a couple more pics of the switch? I can't see the pins clearly, and it would be good to see the other side of the switch.

If there is nothing else in the body of the mic, it seem logical that the loose wires were connected to the switch.

Should be a 1 minute fix once you work out what goes where.

Paul

 

[amanisdude]

Alright. My novice electrical engineering experience precedes me. I think I know how it's supposed to be soldered.

I think that the signal wire in the cord (the red one) gets connected to the microphone's signal wire (either the yellow or white), and the grounding sheath wire gets connected to the remaining one. I believe that when the switch is placed into the "off" position, the microphone drops the signal to ground, effectively sending all the mic audio into the less-resistive cable sheath.

Now the only task that remains is to figure out which of the mic wires (yellow or white) are the signal and ground. As far as I know, signal wires are usually color-coded, which would imply that yellow is 'signal' and white is 'ground'. Can anyone confirm or refute this? White is usually neutral for mains wiring, so I assume it's the same here. But I want to be sure before I solder it wrong! Thanks for any help guys!


‒amanisdude
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[amanisdude]

Hey Paul. Here are the pictures of the switch you requested.

I tried to get as close as possible without losing focus, so I hope they're clear enough. Basically, the yellow wire is soldered to a solder bridge over two of the pins, and the white one is soldered only to one pin. Hope it helps?

















Also, there's nothing else in the body of the mic except for a rigid metal chassis that lines the inside plastic. I don't see any place where any wires could have connected in there. Thanks for your help!


‒amanisdude
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[amanisdude]

Welp, I tried both configurations (red-yellow, sheath-white and red-white, sheath-yellow) with no luck.

I assume this means that either the microphone module itself is messed up, or that there is a break in the wire. Any other ideas I should try before I give up or end up doing something stupid?


This is the current status of the wiring:



Thanks for any ideas!


‒amanisdude
__________________

 

[amanisdude]

Just did a continuity test and found that the sheath is actually ripped somewhere in the cable.

Now just to find out where that is. Short of X-Raying the cable, I have no idea how to do this. :sigh:

‒amanisdude
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[Seidy]

On that last pic soldering like that the switch would be pointless. You are bypassing the switch.

Are you sure there arent any other points where the wires were soldered? Like inside the body or any other place on the capsule.
But yeah, there is always the possibility of broken capsule.


-edit-
so, broken cable.
If you have multimeter then testing should be easy. Connect the meter on both end of same lead and then start twisting the cable inch by inch. Most obvious places would be where the cable meets mic or where cable meets the 6,3mm jack? If you can open (unscrew) the jack then check also the solders.

 

[kip4]

get a new cable and connector and make your own if you can solder your can test it at least. Assuming everything else is ok.
cables and connectors cost just a few pounds

 

[PRHunt]

@amanisdude

If the cable is not simply broken at the connector, then replace it. Loose change will get you a length of coax cable and a 3.5mm jack.

If you do have a continuity tester, I also suggest verifying the operation of the switch. Best to unsolder everything (make note of what was originally attached and where) and just check out exactly what shorts as the switch operates. The apparent solder bridge bugs me a bit.

Paul

 

[amanisdude]

Thanks Seidy, kip4, and PRHunt!

I tried another continuity test, and I am fairly certain that I have isolated the problem to the shield inside the cable. (The resistance in the sheild registers as infinite from one end to the other. )

In terms of making a new cable, I may well do that if I can't find where the break is. I'll try Seidy's idea and try twisting up the cable to see where that gets me.

As for the switch itself, it's in perfect working order. It is my belief that the solder bridge is intentional. When the switch is in the 'ON' position, Pins 1 and 2 (the bridged pins) are only connected to each other, and that sends the signal from the yellow cable directly to the red cable.

But when the switch is set to 'OFF', both Pins 1 and 2 get connected to Pin 3, and that drops the signal from the yellow cable to the cord's less-resistive ground shield, effectively turning off the microphone. (The same effect could have been achieved by connecting only Pin 2 to the signal wires, leaving Pin 1 hanging, but that may have been a bad idea for multiple reasons.)

Anyway, I'll try Seidy's suggestion and see if I can find the break. If I find it (and if it's high enough on the cord), I'll just cut the cord short and solder it from there. (Alternatively, I could perform a minor surgery by opening up the cable at the break and melting some solder onto the shield. ) I'll let you know what comes of it. Thanks for all your help, guys! I'll be back to report how it goes!


‒amanisdude
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EDIT: Note that I am assuming that yellow on the mic is signal, and that white is ground. Do any of you know if this is the convention? Is there a way to test which lead is signal and which is ground for sure?

 

[PRHunt]

Thanks for the update, and good luck!

If in the end you find your mic is dead, you can get a GLS Audio ES-58 or ES-57 (which are clones of the Shure SM-58 and SM-57) from Orange County Speaker Repair for $30 + delivery. These mics receive very favorable reviews.

Keep us posted!

Paul

 

[amanisdude]

Thanks Paul. But that's about $29+delivery above of my range.

Nevertheless, I would love to have a good prosumer mic. I'm in the midst of planning how to webcast a wedding, and the standard handycam mic's don't seem to cut it. I've mostly ended up resorting to lavalier mics that I'm going to mount on the camera and ::ghast:: on a homemade boom. This mic, if it works well, could replace the camera's or the boom's lavalier. LOL

Anyway, if you have any ideas on my last edit to the previous post, that might help me from damaging the mic any further. Thanks for all your help!


‒amanisdude
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[PRHunt]

OK, I may be wrong here, but... because the mic is a dynamic mic with non-balanced connection, I'm tempted to say that the wiring doesn't really matter except in terms of absolute polarity. Someone will no doubt correct me if this is wrong.

I don't believe that there is a standard for wiring colour. Wire it as per your assumption above. If it works and sounds normal, then your work is done.

Paul

PS. Should add, that as the mic is not transformer isolated, you must not let the mic connect to phantom power, otherwise you might see smoke.

 

[amanisdude]

Thanks again, Paul.

Yeah, that is what I thought, but I just didn't want to ruin the mic module.

I do, however, have one more bit of information that I somehow failed to see (and therefore mention here). The microphone is labeled as a CT329 IMPEDANCE 600Ω. It came with an old 486 computer waay back in the '90s.

I'm not sure if that information would help any, but it's worth a shot. I hope it still means the mic leads aren't polarized, but you never know. Thanks!


‒amanisdude
___________________

 

[amanisdude]

PS. Should add, that as the mic is not transformer isolated, you must not let the mic connect to phantom power, otherwise you might see smoke.

I am not sure what you mean by that. LOL.

Despite my rather beginner-level electrical experience, I'm still fresh with the terminology. I don't really understand things like "transformer isolated" and "phantom power". Care to explain what that means in terms of electrical flow and why it may cause smoke? Thanks for dealing with a newb like me!


‒amanisdude
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[Steenamaroo]

I am not sure what you mean by that. LOL.

Despite my rather beginner-level electrical experience, I'm still fresh with the terminology. I don't really understand things like "transformer isolated" and "phantom power". Care to explain what that means in terms of electrical flow and why it may cause smoke? Thanks for dealing with a newb like me!


‒amanisdude
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Stick to jack sockets and you'll be fine.
If for any reason you must connect this to an XLR socket, make sure that phantom power, or 48v, is off.

As far as I can see you have this sussed.
Capsule has two terminals which go to jack sleeve and tip through a switch.
It shouldn't matter which is which, unless you're using two mics. Even then, all you'd possibly have to do is invert polarity of one in your software, which is the same as switching the wires.

As far as the switch, from your description it sounds like it has three terminals which are yellow yellow white.

The on position is yellow connected to yellow, which changes nothing.
The off position is yellow to white, which grounds your audio signal.

 

[PRHunt]

A discussion of audio transformers is best left to the more knowledgeable, but a quick google will reveal more than you ever wanted to know. In brief, a transformer is an electrical component which permits the transmission of a signal between two devices while keeping those two devices electrically isolated. But they do much more than that - making unbalanced signals balanced, for one.

Phantom power is a way of supplying power (nominally +48VDC) to microphones that require it. Active mics (eg condenser mics) need external power in order to charge their capsule, to power a small signal amplifier in the mic, or both. Phantom power delivers this over a balanced connection. Phantom power is typically supplied by microphone pre-amplifiers and can be switched on or off.

Because your mic is not transformer isolated, 48VDC would pass straight through the capsule and most likely burn it out.

Paul

 

[amanisdude]

Thanks for your continued help.

@Steenamaroo ‒ I'll try to keep your phantom power warning in mind, but I don't think I'll connect the mic to an XLR socket any time soon. (For one, I'd feel a bit out of place connecting a 3.5mm jack into an XLR adapter. That just makes me feel uncomfortable. :\ ) Also, thanks for clearing up the polarity issue. That was bugging me a bit. And with regard to the wiring, you are correct. That's actually a much clearer description than mine.

@PRHunt ‒ I assume this means that the phantom power is either delivered through the signal wire or that ground doubles as the signal transmission line. In either case, 48 volts seems like an inordinate amount of voltage to pass through an audio cable, even if the current is low. At any rate, thanks for clearing up transformers in audio signal applications.


Now I must top off my improving understanding of microphones with another dumb question. Would it be okay to replace the microphone's unbalanced coaxial cable with a balanced twisted pair cord (or maybe speaker wire for that matter)? If I can't repair the cord, that would be the type of cheap solution I'd seek out. (If I have to shield it, I'd just wrap the cord in aluminum foil grounded at the plug.) Let me know if that won't work for my microphone, or if there is anything inherently stupid about that. Thanks!


‒amanisdude
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EDIT: Also, I was reading on another forum that dynamic mics aren't affected by phantom power. Not that I'm going to deliver phantom power to my mic (I might get too freaked out by it), but for learning's sake, is the microphone I am working on a dynamic microphone? Thanks again!