Re-Wiring Microphones

[Matt Castore]

So i bought a handful of dirt cheap old mics on eBay, and i need to re-wire them to actually be usable. they are all hardwired, mostly with mini-jack connectors, meaning they have only 2 wires to connect, not 3 like most decent mics. basically my question is: i figured out how to attach a male xlr plug to the end of these so they would connect just like all my other mics, but since these are all high impedance mics, would it be better to attach 1/4" jacks and plug them into the direct ins on my mixer? would plugging a high impedance signal into the xlr input on a board cause problems? any insight would be greatly appreciated. thanks.

[MartinKantola]

If they really are hi-Z mics you could plug into a DI box! You won't get into problems connecting the two wires to XLR pins 2 and 3+1, but might not get a decent signal.

Martin

[dgatwood]

Originally Posted by Matt Castore

So i bought a handful of dirt cheap old mics on eBay, and i need to re-wire them to actually be usable. they are all hardwired, mostly with mini-jack connectors, meaning they have only 2 wires to connect, not 3 like most decent mics. basically my question is: i figured out how to attach a male xlr plug to the end of these so they would connect just like all my other mics, but since these are all high impedance mics, would it be better to attach 1/4" jacks and plug them into the direct ins on my mixer? would plugging a high impedance signal into the xlr input on a board cause problems? any insight would be greatly appreciated. thanks.

If they are expecting a high impedance input and you connect them to a low impedance input, you're loading down the microphone's output transformer. Among other things, you'll lose a lot of the bass frequencies and you may even overload the input and get distortion.

So you should be using 1/4" plugs and plugging them into high impedance inputs.... If you don't have a preamplified high impedance input, you could also use an impedance matching transformer. I definitely would not recommend just hacking an XLR plug onto a high impedance mic.

[dementedchord]

Originally Posted by MartinKantola

You won't get into problems connecting the two wires to XLR pins 2 and 3+1, but might not get a decent signal.

Martin

problems??? how about if he turns on the phantom power for someother mic??? with pin 3 forced to ground with pin 1 he'll roach the phantom....

[MartinKantola]

He won't kill anything even if his mixer doesn't have individual phantom power switches for every channel. Phantom is fed through resistors that limit the current. But phantom is not a good idea with anything unbalanced of course.

My suggestion was to use a DI, or "impedance matching transformer" as dgatwood calls it. An active DI would be fine of course, perhaps even better, especially if the input impedance is higher.

Martin

[Minion]

You can get these Impedance matching Transformers from Radio shack that seem to work OK... They have a female TS on one side and a male XLR on the other side so they not also lower impedance of the mic but they also ballance the mics output.....

Cheers

[dementedchord]

ok... so i should have said you'll burn the the build out resistors if you want to quibble... and not to speak for dg.. but if he meant di i suspect he would have said so... and yes a di will work... not all di's use transformers... and not all impedence matching transformers are di's...

[MartinKantola]

Originally Posted by dementedchord

ok... so i should have said you'll burn the the build out resistors if you want to quibble...

Don't think there will be enough power to burn anything, these resistors are usually metal film and 1/2W. Have you had an experience with burned out phantom resistors?

Originally Posted by dementedchord

and not to speak for dg.. but if he meant di i suspect he would have said so...

My point was that a DI is an impedance matching device, transformer or not, and a good alternative to test with before buying anything. Also, suspect that an active DI would sound better than a cheap Radio Shack transformer.

Martin

[dgatwood]

Originally Posted by MartinKantola

My point was that a DI is an impedance matching device, transformer or not, and a good alternative to test with before buying anything. Also, suspect that an active DI would sound better than a cheap Radio Shack transformer.

Almost certainly. That said, if you're talking about three of them, using active DIs gets a little pricey, which was why I suggested transformers, and specifically, the variety that step down from a female 1/4" to a male XLR.

On the other hand, didn't those cost about $10 apiece just a few years ago? I'm having a hard time finding 'em under $30, at which point you're up in active DI territory.... Sheesh.

[MartinKantola]

For the handy but poor guy a simple DIY project could work, something like this one:

http://web.telia.com/~u31617586/#sim...ce%20converter

(connect the output to PIN 2 and PIN 3 to ground with a 10uF capacitor)

With a handful of additional parts it can be phantom powered so you can skip the battery.

Martin

[MartinKantola]

Just noticed I've recieved bad rep from dementedchord claiming that what I'm saying in this thread is just wrong.

Finding this very unfriendly and hostile, and don't feel to good about participating or trying to be helpful here anymore. Always open to discussions and debates, as there is always something to be learned from others, no matter how many posts or how much experience you might have.

All the best,

Martin

[dementedchord]

ok.. ya want to call me out... i'm here... from my perspective i thought you were being argumentative... not helpful... while i never claim to know everything about this stuff... my credentials are solid... was a pro tech for years... did warranty work for soundcraft/allen and heath/mackie.fender/boogie/korg/yamaha/roland/and others...

[hairylarry]

Matt Castore,

Ok, there's nothing wrong with high impedance mics as long as you keep the cables short. I'd say 10-15 feet max.

I use impedance matching transformers on stage for live sound most often for harp mics or acoustic guitars. They're ok but not the best for recording. In an a/b comparison I can tell the difference between a matching transformer and a preamp.

DI boxes might work better but since I don't have any I can't testify. Maybe someone else can compare signal quality between a matching transformer, a passive DI, and an active DI.

I prefer using my M-Audio DMP-2 preamp. This way not only do I get high impedance in but I also get a quality preamp circuit. The DMP-2 is the same circuit as a DMP-3 which are more common. I imagine other low end preamps like the Rane or the Studio Projects would also provide a high quality solution.

Plugging it into the high impedance input on your mix board will also work but most budget mixers do not have as good a preamp as you will find in the outboard preamps mentioned.

Thanks,

Hairy Larry

[hairylarry]

Originally Posted by MartinKantola

Just noticed I've recieved bad rep from dementedchord claiming that what I'm saying in this thread is just wrong.

Finding this very unfriendly and hostile, and don't feel to good about participating or trying to be helpful here anymore. Always open to discussions and debates, as there is always something to be learned from others, no matter how many posts or how much experience you might have.

All the best,

Martin

Martin,

I've been involved with message boards since the early 80s. Yes before there was an internet I ran the JUG BBS over dialup lines.

As message boards go this one is pretty tame. Many are all flames all the time. Most often these things happen out of a misunderstanding.

Do like I do and ignore all of it. Take what's good and ignore what bothers you.

Thanks,

Hairy Larry

[Matt Castore]

thanks for the help. i finally got around to rewiring these mics just using unbalanced 1/4" plugs. i haven't done any serious recording tests with them, but i tested them out by running them through my ART Tube MP Preamp and into a little guitar amp. they made noise (exactly the type of noise i'd expect from cheap old mics), so as far as i can tell, it's all good. thanks again.

[flyingdisc]

Originally Posted by Minion

You can get these Impedance matching Transformers from Radio shack that seem to work OK... They have a female TS on one side and a male XLR on the other side so they not also lower impedance of the mic but they also ballance the mics output.....

Cheers

And SwitchCraft makes the same type of inline transformer.
Also Whirlwind.... - which you purchase as a DI box -
and so also be useful as that.