Check out this ribbon

[Randy]

Thanks Ned!

That would be some pretty strange physics alright.

[nclayton]

Here's my half assed theory of what happened. I think the brass looking baffle in this mic is earthed, so it's connected to the negative side of the phantom supply. I don't think either side of the primary (the ribbon side) is earthed. I also think the transformer has a short from the primary to the secondary side, and may have had this for a while. The transformer could have still work fine even with a short. Then i think the ribbon was wiggling around and it touched the magnet. That's when some current got flowing from the phantom side through the transformer coils through the primary, through the ribbon and into the earthed brass baffle. Then I think the ribbon let go of the magnet, and like happens with inductors when current tries to stop all of a sudden the transformer formed a high voltage 100mA arc and a big blue spark. Mystery TOTALLY solved. JK.

Ned

[honkyjonk]

Hey thanks guys.

Ned, that's probably the best explanation.

As I was a little more worried about the implications of the Seventh Circle damaging things I've been testing it. Thanks to Tim (I think it's Tim, whoever the 7th Circle representative is) for straightening it out.

I tested measured pin 3 to ground on all the channels and it looks just like pin 2 when phantom is applied, so I think the 7th circle is probably okay. Maybe it's just a bunch of coincidences. Will test with a load applied next.

Anyway, as for the ribbon mic, the transformer is a Cinemag 9888, which is a 1:28 step up tranny.

I just strap an ohm meter across the primary and secondary leads. Testing both pairs of leads seperately? What should I be looking for?

Also, what do you think caused a short in the transformer if there is one?

Is it possible that this problem was caused or escalated if I had somehow reversed the polarity of the Xformer leads when I installed the Xformer?

[nclayton]

Ned, that's probably the best explanation.

I don't know about THAT, but it would sort of explain it. No matter how you jack up the voltage, though, it's still a little hard to figure out where the power to do that kind of damage would come from if you're just looking at a phantom supply. It might be so, but it I'm not ACTUALLY convinced that will be it.

I just strap an ohm meter across the primary and secondary leads. Testing both pairs of leads seperately? What should I be looking for?

Also, what do you think caused a short in the transformer if there is one?

Is it possible that this problem was caused or escalated if I had somehow reversed the polarity of the Xformer leads when I installed the Xformer?

To test it you can measure resistance from any lead on the primary to any lead from the secondary. On a good transformer obviously that should be basically infinity. If there's a short you'll see between like 0 and probably something like a couple hundred ohms at the very most on a transformer like that.

I mean....to be honest you don't really see shorts between windings in low power transformers very often, but it's conceivable. If so, the best explanation is just defective transformer. Like I say, if there WAS a short, it could have been there forever and the transformer could still basically work and sound totally fine.

I don't think reversing leads would make things worse or more likely to break down.

I said I'd bet you have a short...from the symptoms it seems like it would make sense. But based on how often that actually happens with little tiny low power transformers I think if it came down to it I'd probably only actually bet maybe no more than about two bucks on it. That's how sure I am.

Ned

[audioboffin]

Even with phantom off, my sytek measures something like 2v dc across all 4 channels.

That 2V difference could also disappear if you measured across a realistic load instead of an open circuit.

If the microphone is "the load" then the microphone is dissipating the current and the transient induced across the mic's transformer when you plug in could well be enough to fritz the ribbon. My sympathies! Now it's time to buy some aluminium foil and invest some time in cutting, corrugating and tensioning a new ribbon!

I have a couple of preamps that I specifically use for ribbon mics and these preamps don't have a phantom power supply any more. I position them on the floor close to the mics and am very careful to run cables from the ribbons to the specific preamps.

Once bitten, many many many times shy!

[honkyjonk]

Yeah, I was thinking about rolling my own, but the aluminum or whatever it is that is covering the magnets is peeling back too. I'm not sure if that's important or what. Might be diminishing returns.

I'm just glad it wasn't my M160.

[audioboffin]

It looks like there was enough current for the burn to spatter out to the sides!

You might be able to either get a replacement "motor assembly" or an assembly with a torn ribbon from someone who has blown it out and just bought a full assembly to replace, then re-ribbon that.

I went through a similar experience with a lollipop shaped ribbon mic, coincidentally it happened when I was miking a bass cabinet for a live recording. Sadly, the monitor guy was wrong when he told me the phantom power was off on that channel, and the ribbon was blow out of the gap. It sat on my desk at home for 8 months before I got around to making a ribbon for it. Took some fiddling to get the tension right, but definitely worth while doing, the mic now sounds a lot better than it shipped.

Very lucky it wasn't a valuable vintage mic!

[micyourbrain]

poor you. today i was LOVING my modded apex 205 with the LL2913 tranny and it sounded awesome on everything vocals acg gtr, electric guitar amp

sorry to rub it in

[SeventhCircle]

If the microphone is "the load" then the microphone is dissipating the current

Not if the dynamic or ribbon mic is wired correctly. If the voltage between pins 2 and 3 is 0V, which is what it should be regardless of whether phantom is on or off, no current will flow.

and the transient induced across the mic's transformer when you plug in could well be enough to fritz the ribbon.

Hot plugging mics is bad practice, but you'd have to be pretty unlucky to destroy a properly wired ribbon mic simply by plugging into an XLR with phantom power present. The real hazard is when phantom power is run through a patch bay. Here's what Royer has to say about it: http://www.royerlabs.com/faq.html#7

[audioboffin]

If the microphone is "the load" then the microphone is dissipating the current

Not if the dynamic or ribbon mic is wired correctly. If the voltage between pins 2 and 3 is 0V, which is what it should be regardless of whether phantom is on or off, no current will flow.

and the transient induced across the mic's transformer when you plug in could well be enough to fritz the ribbon.

Hot plugging mics is bad practice, but you'd have to be pretty unlucky to destroy a properly wired ribbon mic simply by plugging into an XLR with phantom power present. The real hazard is when phantom power is run through a patch bay. Here's what Royer has to say about it: http://www.royerlabs.com/faq.html#7

All it takes is for pins 2 and 3 of the XLR to not make contact at EXACTLY the same time and the damage is done, hot patching a bantam almost ensures that this is the case. This is probably the most common cause of damage to ribbon mics, closely followed by ribbons being stretched/broken by inappropriate proximity or use without a good pop filter.

[SeventhCircle]

All it takes is for pins 2 and 3 of the XLR to not make contact at EXACTLY the same time and the damage is done

Ohm's Law: I=E/R

If E is 0, I is 0. It doesn't matter who touches what first. When phantom is off, the voltage between pins 2 and 3 is 0-0=0V. When phantom is on, the voltage between pins 2 and 3 is 48-48=0V. No voltage means no current.

hot patching a bantam almost ensures that this is the case

Hot patching a bantam with 48V at the tip and ring almost ensures that first one side and then the other will be grounded as the plug drags across the shield contact on the way in. That's how you get a DC voltage across the signal lines, and that's what does the damage.

[audioboffin]

All it takes is for pins 2 and 3 of the XLR to not make contact at EXACTLY the same time and the damage is done

Ohm's Law: I=E/R

If E is 0, I is 0. It doesn't matter who touches what first. When phantom is off, the voltage between pins 2 and 3 is 0-0=0V. When phantom is on, the voltage between pins 2 and 3 is 48-48=0V. No voltage means no current.

Seventh Circle, agreed in pure theory, but in practise if there is any electrical path at all from the ribbon down to the mic's chassis (pin 1) then applying a momentary voltage across say pins one and two induces a spike across the primary of the transformer. That's what causes the damage to the ribbon in circumstances that otherwise may seem impossible. In the OP's example, it would appear that the ribbon may have sagged in the gap and touched the magnet structure. I'm with Ned

Being tardy about phantom power is what kills ribbon mics and the reason why I now never lend them out!!

[nclayton]

Seventh Circle, agreed in pure theory, but in practise if there is any electrical path at all from the ribbon down to the mic's chassis (pin 1) then applying a momentary voltage across say pins one and two induces a spike across the primary of the transformer. That's what causes the damage to the ribbon in circumstances that otherwise may seem impossible. In the OP's example, it would appear that the ribbon may have sagged in the gap and touched the magnet structure. I'm with Ned

I basically agree with 7th circle, though. The only reason the little scenario that I wrote earlier would work is because I was speculating that maybe there was a fault in the transformer. If the transformer is good then nothing I said would happen.

I'm not saying it's a bad idea to be sure phantom is off before plugging in a ribbon, but if the mic is correctly wired with the secondary floating, then it doesn't matter how many XLR pins are attached. I know it's easy to visuallize that 48 volts reaching out and doing something bad, but I think a good thing to remember is that it takes POWER to snap or even vibrate a ribbon (not much power, but power) and you can't get power without both voltage AND current. You just can't get any current to flow in a phantom circuit without some sort of return path to ground, and if the mic's output is floating there's just no return path regardless of whether one or both pins are attached. Current can only flow from 48 volts to zero volts, NOT from 48 volts to a dead end (like when only one pin is attached) and NOT from 48 volts back to 48 volts (like when both pins are attached).

technically, there IS a little capacitance between the output transformer coils. If one side of the ribbon's grounded then when the phantom first gets applied (whether through 1 or 2 pins, it doesn't matter) a little current can flow out of that capacitance to ground. This is a really small capacitance, though, and don't forget that whatever current it takes to fill it up has to come out of the 6.8k resistors and travel through the inductance of the transformer as well. That's going to be a very small, very short duration spike, and I'd guess it's not worth worrying about.

I think the problem with ribbons and phantom and the origin for all the caution comes partly from the fact that quite a few of the old fashioned ribbons are either internally wired unbalanced or have grounded center taps on their secondaries. No modern ribbons are wired this way unless they were designed by crazy people. The rest of it's based on the hot patching problem that you guys already talked about.

[ulriggribbons]

My take is that the paint peeling from the magnets is a manufacturing defect that often prevents the microphone from functioning properly.

I saw this quite a bit on the early incarnations of these microphones.

The ribbon also appears damaged, whether by a wind source, phantom, or by removing the paint flakes (where's the rest of the paint, by the way? ).

$.02 =)

ju

[Marik]

Most magnet manufacturers use not paint, but electroplating. I never saw the plating peeling when magnets are straight from the factory, but it could easily happen when two magnets clash at each other (and those things are STRONG) with high velocity--then the Nickel plating starts bubling.
It could happen during mic assembly. If left unnoticed, I could see how the ribbon and magnet could melt like that.