Dynamic Microphone switch wiring

[PRHunt]

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!

I think the shielded coax is better.

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!

Dynamic mics are not affected by phantom if they are transformer isolated. If a dynamic mic has balanced output, it is almost certainly transformer isolated. Most pro audio dynamic mics will be made in this way.

Your mic is almost certainly a dynamic mic, but without a transformer.

Paul

 

[kip4]

Shielded cable every time for mics in my opinion.
Should be an easy fix.

 

[amanisdude]

Thanks guys.

So, I've spent a good chuck of yesterday and today on this project. I've hooked my multimeter up and twisted and turned my cable like there's no tomorrow, but when measuring for resistance from one end of the cable to the other, my measurements vary continuously and wildly between 300 ohms to 1500 ohms. (I think the lowest stable reading I've gotten is around 320 ohms.)

Does anyone here happen to know what the nominal resistance for a microphone's cable shield should be? (At the jack, the resistance can be as low as 2 ohms!) I keep cutting the cable to where I think the break is to find that it seems to be further down. Knowing the normal resistance range would be very helpful. I know I've taken up a lot of your time for this little repair project of mine, and thanks for all your help!


‒amanisdude
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[kip4]

you should be using the meter to test for contunuity not "resistance", To see where the break is.
once you have cut a chunk off and you get continuity on both cores then you should be past the break in the cable. Hopefully.

 

[PRHunt]

you should be using the meter to test for contunuity not "resistance", To see where the break is.
once you have cut a chunk off and you get continuity on both cores then you should be past the break in the cable. Hopefully.

I agree. However, even checking resistance, we should only be seeing very low resistance.

Example: I just grabbed a 5 metre mic cable. Resistance of the shield (pin 1) end to end was under 1 ohm. 320 ohm is too high.

Worth checking the batteries in the meter, by the way. Check the leads of the meter as well - be sure you get 0 ohms when you touch the probes together.

Paul

 

[amanisdude]

Touching the probes together yields me a value as low as 0 ohms, but it can give me momentary readings as high as 60 ohms if I slide the test leads across each other!

In terms of the master batteries, it's a new multimeter ($10 from Fry's), so I assume the batteries should be in good working order unless it's been on the shelf for a while. (Also, testing on the signal wire in the cable does in fact give me around 1 ohm, so I assume it's working fine.)

As for the continuity testing, on my multimeter, a continuity test is the same as a resistance test. Both output the value in ohms. Good catch, though!

At any rate, I'll keep fiddling with the cable until I can find the true break. I've already gone through about a foot of cable, so I'm beginning to think the break may be more toward the middle. Thanks for clearing up the normal resistance value, though! Now I have something compare it against (although I did initially assume it should be the same as the resistance in the signal wire; I guess that should have been obvious ).


‒amanisdude
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[gecko zzed]

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!

You are going through all of this to record a wedding, right? And a wedding is kinda special to some people, right? Specially the bride and groom. So there could be a few disappointed people if it doesn't work out.

So why not minimize your risks and get some decent balanced microphone cable? Think of it as an investment in the future.

I appreciate the McGuyver-like ingenuity of your solutions, but wrapping aluminium foil around speaker wire is something you would do if there was no other solution at hand. You may be lucky and it might work, but it smells like trouble to me.

 

[amanisdude]

Arg! Alright, I've just about given up. Every time I think I've found the break in the shield, I cut the cord at that point only to find that the break is somewhere further down!

gecko zzed might be right:

You are going through all of this to record a wedding, right? And a wedding is kinda special to some people, right? Specially the bride and groom. So there could be a few disappointed people if it doesn't work out.

So why not minimize your risks and get some decent balanced microphone cable? Think of it as an investment in the future.

So, does anyone happen to know where I might be able to buy a shielded microphone cord at a relatively inexpensive rate (including shipping to the San Francisco area if sold online)?

So far, the best I have been able to find are:

• Carol Cable 1399 Single conductor mike cable by the foot - from Wholesale Electronics
• Mogami W2368 Miniature Unbalanced Microphone Cable

And I'm not sure if either are the best for my needs. Is there a better cord or place?
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To review the details of the device, my mic is labeled as a CT329 IMPEDANCE 600Ω, and it is a dynamic handheld mic that I got with an i486 computer some 15 years ago. The cord is a shielded cable with a single lead that is a stranded 22 AWG (I believe) wire. It has a permanent cord (no XLR), and it terminates with a mono (TS) 3.5mm plug. Also, remember that I'm pretty strapped for cash, so the more inexpensive for quality, the better. But any help would be very much appreciated! Thanks all!


‒amanisdude
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EDIT: Alternatively, you could point me to the best way to make a shielded microphone cable if that's cheaper. I would definitely learn a lot more.

 

[Seidy]

Since you are not completely sure the cord is the problem I'd go and rent a mic and the cable. And make sure the cable is the right one.

(i just looked at the pic's of this mic... there is something that I don't trust about these mics )

 

[amanisdude]

Since you are not completely sure the cord is the problem I'd go and rent a mic and the cable. And make sure the cable is the right one.

(i just looked at the pic's of this mic... there is something that I don't trust about these mics )

Well, "not completely sure" is probably in the 1% uncertainty range. I'm fairly certain that the cable is the problem and that the capsule is in perfect working order.

Rentals are always an easy fix... if you have the money. As for me, I'm trying to keep this whole project as cheap as possible, and that means that I'll only be doing highly necessary rentals. (Heck, it may even be cheaper to just buy a new microphone in my case.)

But if you still think I should be renting, humor me please. I really do want to fix this mic, whether for this particular project or another. There's just something about having an unusable mic with only one issue that's in otherwise perfect working order that just bothers me. Thanks!


‒amanisdude
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[PRHunt]

Rentals are always an easy fix... if you have the money. As for me, I'm trying to keep this whole project as cheap as possible, and that means that I'll only be doing highly necessary rentals. (Heck, it may even be cheaper to just buy a new microphone in my case.)

Hmmm. Well I did spot this: Amazon.com: Creative Labs handheld Microphone: MP3 Players & Accessories

 

[amanisdude]

Hmmm. Well I did spot this: Amazon.com: Creative Labs handheld Microphone: MP3 Players & Accessories

Heh, well, I have noticed some cheap mics on ebay. I suppose I could buy one of these, then take off the cord and put it on my old one, but then I'd just have a different nonfunctional dynamic mic lying around.

Anyway, I guess I'll shop around the Interwebs until I find a cord that looks right for the price. How do you think that Carol Cable would be for my application? Or, better yet, how about taking one of these and chopping off the connectors, then soldering the cable to mine?

In any case, I may no longer be finishing this project for the wedding, but now I'm just curious. How would one find or make a replacement microphone cable? Thanks, guys!


‒amanisdude
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[PRHunt]

The Carol Cable should do the job. Just do it!

 

[Steenamaroo]

Ok. it was a fitted cable right? As in soldered inside the mic?

Remove it and test the shield with a continuity meter, then test the other conductor too.

If you don't have a meter, get a battery and a bulb. Make a circuit using the two ends of the shield, then the two ends of the signal conductor. Obviously if the bulb lights, there's no break.
If you don't have a battery and a bulb, take them out of an old torch or something.


If there is a break, I wouldn't chase it, but if you really want to cut it in the middle. The fault has to be on one side right?




Since it's a 3.5mm end on your cable, an old pair of headphones or an old jack to jack cable would provide a perfect replacement.

Obviously that'll be TRS, so find out which of the two conductors corresponds to your jack tip (use a meter, or circuit test above), then just join the other one to shield at both ends.

Hope that's helpful.

 

[amanisdude]

Haha, thanks Steenamaroo!

Remove it and test the shield with a continuity meter, then test the other conductor too.

Done and done! The signal wire in the cord is in perfect working order. The shield, however, is the problem. The resistance in the shield conductor varies between 200 ohms to 1500 ohms, up to infinity! So I'm sure there's a large break somewhere in the cable with only a few copper fibers touching at a time.

If there is a break, I wouldn't chase it, but if you really want to cut it in the middle. The fault has to be on one side right?

Haha, I've thought about that. My only concern about that it would make the cable only half of what it is, and the cable is already fairly short for a mic cable. Nevertheless, I may have to resort to something like that if I really can't pinpoint the break.

At any rate, I think the Carole Cable 1399 would work best, though the shipping is a bit through the roof (4.5x the actual product price!). The other option is to install an XLR port on the base of the mic and use a standard mic cable. ^_^" I might consider that one, too.


‒amanisdude
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