How to protect a transformer-less mic?

[puddingstud]

Sounds like maybe the coil is stuck. It may have been pulled into the gap when the power was applied and got stuck. In that case it would still pick up handling noises but not function properly as an acoustic microphone. It would be worth removing the grille to have a look.

Meaning it's repairable?
I opened it but all I saw was a normal diaphragram.

If this is the case, it would still imply a misconnection at some stage, as there would have been enough current flowing through the coil to pull it into the magnet.

I'm not getting it. What kind of misconnection, an example?

 

[MagnetoSound]

Meaning it's repairable?
I opened it but all I saw was a normal diaphragram.

Does the diaphragm move in and out if you touch it gently with your finger? If so, what sound can you hear from the output?

I'm not getting it. What kind of misconnection, an example?

The faulty cable we’ve been discussing, for example. Or even maybe somebody blew hard into the mic and damaged it?

There is more than one way to destroy a microphone, after all.

 

[puddingstud]

Does the diaphragm move in and out if you touch it gently with your finger? If so, what sound can you hear from the output?

The diaphragm is the transparent plastic part? Yes it moves, and it produces "pop" sound.

The faulty cable we’ve been discussing, for example. Or even maybe somebody blew hard into the mic and damaged it?

There is more than one way to destroy a microphone, after all.

And I said, I was home, I only plugged it, and the cable seems 100% fine.

 

[Migs 31]

I think the only way to break a dynamic capsule without a transformer is if the cable is unbalanced (pin 1 to pin 2 or pin 3) or accidenly damaged.
With a unbalance cable the coil in the capsule gets the whole +48Volt and gets destroyed...

Pease explain this someone:
Not an SM-57 this one, rather a AT805b electret I guess, with an LH1130 battery inside.
The previous owner changed the usually 1/4"Jack (unbalanced connector) to an XLR.
Silver (shield) is Pin 1- Red (signal) Pin 3 - Nothing on Pin 2 and he left a yellow wire cut, hanging ?!!?
Therefore that means the poor thing is getting the full 48V on pin 3 when in use with condensers, as this Mackie mixer only has a general +48V switch ?!?

When I think about it, I hear hum when I switch the Phantom power on, only appears on this mic.
But he is still alive!

@Khron "Transformerless, you say? How is it (re)wired internally, then?"
Ok, for the allegedly damaged "naked" SM-57. But in my case, clearly not a coil diaphragm,
there must be some sort of FET or circuit inside this little fellow? I cannot open the darn thing.

M

 

[Khron]

Therefore that means the poor thing is getting the full 48V on pin 3 when in use with condensers, as this Mackie mixer only has a general +48V switch ?!?

That could indeed be an issue - especially if it's battery-powered, and only had a TS jack from the factory, it likely has some DC-blocking capacitor inside. But that's gonna be reverse-biased when phantom-power is applied to it. Not sure one can fit too large a value of film (or otherwise non-polar) capacitor in there, so it's likely electrolytic, but AT wouldn't have had much reason to use a bipolar one there, so...

Yeah, cracking it open would indeed be useful

PS: Found an eBay listing for a (sold) 2-page manual for the thing! Since it's battery-powered, i figured there must surely be SOME way to replace it

 

[Migs 31]

That could indeed be an issue - especially if it's battery-powered, and only had a TS jack from the factory, it likely has some DC-blocking capacitor inside. But that's gonna be reverse-biased when phantom-power is applied to it. Not sure one can fit too large a value of film (or otherwise non-polar) capacitor in there, so it's likely electrolytic, but AT wouldn't have had much reason to use a bipolar one there, so...

Yeah, cracking it open would indeed be useful

Thanks for your reply,
I would like to crack it open like you say. But hey, it's still working and it sounds good on live acoustic guitars (strange enough).
I was wondering if adding a blocking capacitor on Pin 3 (signal) would get rid of the hum?
But you think there is one in there already?

But hey, i'm hijacking this thread : let's go back to OP - SM-57
M

 

[Khron]

But you think there is one in there already?

I updated my reply in the mean time

 

[Migs 31]

I updated my reply in the mean time

Darn you, @Khron microphone/gear sleuth ! (thats a compliment actually, not an insult).
Thanks.
M

 

[puddingstud]

The diaphragm is the transparent plastic part? Yes it moves, and it produces "pop" sound.


And I said, I was home, I only plugged it, and the cable seems 100% fine.

Up++

 

[puddingstud]

Back again!
This:

Besides, there usually are caps on the 48V rails on every channel. If these unload their stored energy because someone disconnects the XLR, the discharge of these caps could be very bad and the two caps in series with the signal might just pass enough energy to blow a dynamic mic. It gets worse on recapped mixers where the adagio is "put higher values everywhere".

Out of panic when seeing phantom power on, I guess I've hot-unplugged the mic. Could it be the reason of its breaking?

 

[gyraf]

by unplugging a xlr? no.