How to protect a transformer-less mic?

[Hank Dussen]

How can I protect a transformer-less SM57 against phantom power?
Will simple blocking caps do?
If so, what value?

 

[3nity]

i dont think a SM57 will go bad if 48V is turned on!

 

[nickeveslage]

An SM57 will not be harmed. I've heard people say that they can hear a difference in sound ( a very, *very* slight difference ). I'm not sure I buy it.

 

[okgb]

Some have been modded by removing the
average grade output transformer
[ said to , i haven't tried it yet make it
a little more open & smoother at the cost
of more noise on low level because of impedance change ? ]

 

[Hank Dussen]

Indeed, as I said it's a trasformerless made SM57.

http://homerecording.com/bbs/showthread.php?t=273513
http://thehuxcapacitor.wordpress.com/2009/09/10/sm57-modification/
etc...

 

[MagnetoSound]

It's safe to use as you normally would.

 

[Hank Dussen]

Just took the transformer out of one of my 57's.
Still a little worried about possible damage by phantom power tough.
I found this on the net:

"If you are worried about that, (some consoles don't have phantom switches like older Harrisons) just wire one cap in series with each one of the wires to the capsule. Use a cap rated at 50 volts or more. A 47 uf ought to do, just place them so the + pin faces the XLR pins. Use a good cap like Panasonic FM or Nichicon HE, bypass with a quality polyprop film cap for more details."

But, wouldn't it be more logical if the lythics + is facing the capsule?
Anyone?

 

[wmtunate]

But, wouldn't it be more logical if the lythics + is facing the capsule?
Anyone?

no, because the phantom voltage is coming from the preamp

 

[Hank Dussen]

Thanks. Just wanted to make sure.

 

[abbey road d enfer]

How can I protect a transformer-less SM57 against phantom power?
Will simple blocking caps do?
If so, what value?

A standard SM57 with transformer doesn't have capacitors; does it worry you?
If the answer is no, why would you have capacitors when you have a direct connection to the capsule ("transformerless")?
Phantom power has been designed in such a way that dynamic microphones should not be harmed by it.
There's a risk only if there's a wrong connection.
The whole idea is that the capsule (or transformer secondary) is floating vs. ground; both hot and cold conductors are at the same DC potential so there's no current.
Whatever improvement brought up by the "transformerotomy" (ablation of the transformer) may well be diminished by the addition of electrolytic caps.

 

[Hank Dussen]

I understand that within normal circumstances phantom power should not harm even a transformerless microphone but circumstances are not always normal. Especially live.
Anyway I'll try it with and without caps and compare.

 

[Rossi]

Most moving coil dynamic mics these days are transformerless by design. None of the current Beyerdynamic moving coil dynamics uses a transformer. The Shure SM57/58 are an exception to the rule.

In fact, a lot of dynamics were transformerless even in the 50s and 50s. Transformers were mostly used for mics offered two or more output impedances for interfacing with home, semipro and studio equipment. Some of the SM58's predecessors had an internal switch for hi and low impedance. Hi impedance is useful for plugging a mic directly into a guitar amp, for instance.

A dynamic mic won't see phantom power - P48 is specifically designed for that. The coil is wired to Pin2 and 3, which are on the same voltage potential. Even if there is a small voltage difference due badly matched phantom power resistors, it's not likely to harm your mic. Moving coil dynamics are quite rugged.

 

[puddingstud]

Hi guys, I've tested that for you: transformerless SM57 DOESN'T LIKE phantom power. Mine broke after 1 minute, under normal circonstances (RME soundcard).
Thanks to all for great forum advice!

 

[cyrano]

Just took the transformer out of one of my 57's.
Still a little worried about possible damage by phantom power tough.
I found this on the net:

"If you are worried about that, (some consoles don't have phantom switches like older Harrisons) just wire one cap in series with each one of the wires to the capsule. Use a cap rated at 50 volts or more. A 47 uf ought to do, just place them so the + pin faces the XLR pins. Use a good cap like Panasonic FM or Nichicon HE, bypass with a quality polyprop film cap for more details."

But, wouldn't it be more logical if the lythics + is facing the capsule?
Anyone?

The phantom spec specifies a max. voltage of 54 V. If one cap blows, the protection is worse than no protection. I've occasionally seen higher voltages on mixers that had no load attached.

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".

I personally don't worry about it. As long as your cables are correct and you cut phantom power before disconnecting a mic, it should be OK. Besides, the SM57 isn't expensive and still available new, so I don't see the problem.

OOPS. Just noticed I was participating in some thread necrofilia. Sorry.

 

[cyrano]

Hi guys, I've tested that for you: transformerless SM57 DOESN'T LIKE phantom power. Mine broke after 1 minute, under normal circonstances (RME soundcard).
Thanks to all for great forum advice!

If that happens, the RME, the cable, or the mic have an error in the wiring...

 

[puddingstud]

If that happens, the RME, the cable, or the mic have an error in the wiring...

Such as? I can easily test but it seems very very unlikely to me.

 

[cyrano]

As Abby already explained above, phantom can't damage a mic if the cable is wired correctly.

 

[puddingstud]

As Abby already explained above, phantom can't damage a mic if the cable is wired correctly.

If so, it seems that "the cable is wired incorrectly" is not a uncommon situation; thus it IS dangerous.

I'm a bit angry as I first heard I had to be careful about Phantom Power; then I read in the forums it was wrong; then I broke my 70€ mic.

 

[cyrano]

You could've switched off phantom power...

Besides, it's worth repairing the cable as it will certainly affect the sound too.

 

[thomasdf]

Hi guys, I've tested that for you: transformerless SM57 DOESN'T LIKE phantom power. Mine broke after 1 minute, under normal circonstances (RME soundcard).
Thanks to all for great forum advice!

So you really created an account on GDIY to complain in a 2011 thread, when you could have switched off your phantom power before using your mic ?

On a side note, I much prefer my 57 without its transformer. it took phantom power accidentally from time to time and still performs fine.