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Figure-8 Mics, ribbons and 48V Phantom Power

I'd read a few internet posts over the past few weeks about ribbons, and they pulled up the old advice about destroying them with phantom power, so I did a little Googling and also noted many newcomers to recording really didn't ever come across fig-8 pattern mics at all - so I've been doing a few videos and did one featuring just a bit of chat about fig-8 patterns and a little demo of how they actually sound when you move the mic - then I figured I'd plug up a ribbon in place of the condenser and see if it broke - as the usual tales of doom decree they do.

Comments

paulears Thu, 03/24/2022 - 14:19

audiokid wrote:

excellent video, Paul.

Thanks for that - The whole series of videos was just a whim really. Not made in my audio studio at all, but in my video studio half a mile away. I bought the metal desk and put it together in the space, and then figured I had plenty of gear, including some bass PA type speakers, and as Cubase 12 now allows multiple installs I put that on the office MacBook and the Mac was happy talking to a retired Lexicon interface I replaced because they stopped doing drivers - but the Mac didn't need them! The video studio is quote dead, mainly because all the walls have flight cases and boxes against them, and then coloured background cloths - White, green, blue and black and they all hang and I just change the order for the video jobs. They seem to really tidy up the sound - a total accident really. I made one video to see how time consuming they'd be, and then I did one when I'd been doing something. I think I'm also the only person who isn't excited by having some nice mics - the differences in the main are quite minor, and it's interesting to find that the SM7B - A mic I really didn't see the point of, actually has become my default mic. It also works really well at a distance. With the Cloudlifter preamp, I'm not using it close at all, and I now like it, but it's worth watching the very first video I did to hear the comparisons.

 

audiokid Thu, 03/24/2022 - 16:16

Yes, looks really good and the sound is excellent. 
I’ve wanted an SM7B for years. They look good, have a nice way to connect the cable and seem to have the perfect frequency focus. 

What preamp are you using for it ? 

audiokid Fri, 03/25/2022 - 09:04

I just reread you comment. I've never used a "cloudlifter". I had no idea it was an actual preamp. I thought it was just a booster people used to add extra level for ribbon or dynamic mics. I need to look at those again.

paulears Fri, 03/25/2022 - 09:12

audiokid wrote:

I just reread you comment. I've never used a "cloudlifter". I had no idea it was an actual preamp. I thought it was just a booster people used to add extra level for ribbon or dynamic mics. I need to look at those again.

The SM7B actually works fine into all my preamps if I use it close in - which is how you see many people use them - and I think they're pretty ugly, and maybe even gimmicky - but when I got the pre-amp I discovered they're a great way of letting you work at a distance with SM7B (and the EV320 I have). The ribbon has a pretty decent output to be fair, but I do have a couple of commentators ribbons, and the difference a cloud lift makes on them is very obvious. I actually thought mine was faulty, so got another and discovered they were the same - adding a preamp makes them much nicer to use.

audiokid Fri, 03/25/2022 - 09:42

Thank for explaining.

I had an idiot do exactly what you mentioned to a Royer R121 of mine. It ruined the ribbon right away. Luckily Royer replaces the first ribbon at no charge.

Bertel37 Thu, 04/21/2022 - 05:16

The discussion about the demolition of ribbon microphones by phantom power (pp) is an old controversy. There are 2 leagues pro and con. Lets examine the situation in detail:

a) There are 2 very different cases with respect to applying the phantom power to the microphone: Static and dynamic behaviour.

b) There are 2 different cases of failure of the microphone: Thermal destruction or bending of the ribbon out of the magnetic field

a-1) The ribbon transformer does not transfer any DC to the ribbon. It also does not transfer very low frequency transients below the low frequency edge of transmission. Thus:

Static case - assumed the microphone is completely connected to the amplifier - pp transforms no DC current through the secondary winding of the transformer to the ribbon. There is no risk of harm, when pp is on. However the core may be magnetised and loose performance.

a-2) Dynamic case 1

Same assumption – switching pp on usually generates a slow rise in voltage up to nominal supply voltage, as in most cases, pp is generated by charging a large capacitor. In common, this slow rise is not transmitted to the ribbon and does no harm either, since the rise is symmetrical to both lines.

In rare cases however pp might be applied by switching the pp directly using a double throw switch to the 2 legs of pp resistors (usually 6.8 kOhms). Symmetry is lost. This has the same effect is described in dynamic case 2.

Dynamic case 2

The microphone gets connected with pp on. Simultaneous plug in of both pins is never true. There is a fast transient produced by a source of 48 V/6.8 kOhms (7 mA) transformed to the ribbon. Cable capacitance is sufficent to transfer this spike. Assuming a common transfer ratio of 1:35, the primary current fed to the ribbon may be up to 247 mA. This may either blow the ribbon apart (b1) or (b2) bend it out of the magnetic gap. In the first case, the microphone is dead, in the second case it is more or less degraded. The better the microphone, the more likely is the damage !

Since you never know exactly what is behind your equipment the moral is:

NEVER use pantom power on a passive ribbon microphone unless you rely on luck!

BTW: I have tried the above with my own specially constructed ribbon microphones with an extended response up to 35 kHz using very thin ribbons. They were immediatly dead !