Ribbon Mic Blown the Hell Up!

[quote author="PRR"]
Transformers pass THUMPS. The damage, if any, is done in around 10 milliSeconds.[/quote]

Just today was playing with my ribbon--I grounded electrostatic shield of the trafo with mic "on". The ribbon had a thump with excursion of at least 1/4".
I use phantom with my ribbons all the time, never had problems. But on the other hand, even if I have, I don't really care--time to try another foil :grin:

I used to build pulse transformers.

In high school I used this thump/spike method to shock the hell out of my friends/victims.

with a 12V transformer from radio shack and a AA battery on the secondary I could get quite a ZAP out of the primary.

I'd say something like "hold these two wires....how could a AA battery hurt you?"

And I wonder why I didn't have many friends in high school... :shock:

Worth noting that when the DC voltage is REMOVED is when you can get big spikes from the collapse of th magnetic field. Thats how contact breaker auto ignition works, you get the spark when the points OPEN.
TV flyback line circuits use a diode to rectify the puse and add it to the HT rail.......but thats another story.
Steve

[quote author="buttachunk"]here is my Ribbon Mic Saver;
(patent pending :green: )

http://img.photobucket.com/albums/v251/buttachunk/ribbonmicsaverpic1copy.jpg

J1 is the XLR connector. C2 is between the mic's internal ground and J1.


the cap values may be too large for some, but this should protect surges, imbalenced DC current, and misconnection mishaps...[/quote]

One year later I finally got around to building this circuit. Regarding the cap values, I don't find that they are large enough. With my 270 ohm Shure 55SH (not trying the ribbons until I am really sure--although I've got 0V between both pins and ground, so all seems fine), I'm getting significant bass rolloff with the 0.1 uF values. I needed 3.3uF to be happy and 10uF to be completely satisfied. Is there likely something wrong with my circuit :?: My ribbon is 150 ohm, so wouldn't it be worse off, or do I have that backwards?

the ml52 shoul be o..k. with phantom. I have one I hit it with phantom once and no biggie. As I recall, Phantom is bad for the old ribbons not the newer designs in fact 48V is o.k. but not recomended but T-power instant death.T-power the precurser to phantom is a no no hense why it's often said no phantom on a ribbon mic

The phenomenon here is called "inductive kick". It is what gets a 12 volt auto battery to deliver tens of thousands of volts to a spark plug.
While it's true that a transformer will not pass DC, at the moment of connection (or disconnection) DC is not DC. It is a changing voltage of close to infinite frequency (O to 48 volts in close to zero time).
The transformer has a magnetic field built up during the connection and a collapsing field during disconnection. This field flux induces a momentary voltage spike the secondary. That is, after all, what transformers do.

In a properly wired ribbon mic - cable - preamp input system, not only does the primary see phantom on both legs simultaneously, so no differential and no current flow, also there is no path to ground so again no current flows and therefore no inductive kick. If the transformer or mic cable is miswired or shorted in such a way that one leg of the system is grounded problems can arise.
Lots of studios have been using ribbon mics with consoles that do not have per-channel phantom for decades. The phantom is always on. Lots of Neves are like that. That's why some people will tell you that phantom killing a ribbon is impossible. Even though I know it's not likely to be a problem, I still triple check to be sure it's off before pluging a cable into my R*yer. It can be a very expensive way to discover a bad cable.
Depending on the turns ratio of the transformer and the magnetic characteristics of the core, a very large momentary voltage can be generated. That's why bluebird could shock his friends holding the primary of his 12 volt radio shack transformer with a 1.5 volt battery on the secondary.
I've destroyed an SM57 with phantom and a bad cable. It sounded like a kernel of popcorn popping when the diaphragm tried to jump out of the mic case.