Old 09-02-2018, 09:39 PM   #1
ReaperGuy
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Default 48V mic

Hi Folks,

I recently bought a couple of good Neumann mics and don't want to mess them up!
I know they need 48V to operate but I'd like to understand the difference between 48V and 48V phantom power.

They obviously didn't come with a power supply.

I have an Edirol UA-25EX audio interface. There is a 48V Phantom switch on the back.

Do I just plug in the mics into this interface and connect to my computer/Reaper to record?

If you could explain these basics to me I'd appreciate it!
Anything I need to be careful about?
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Old 09-02-2018, 10:10 PM   #2
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Don't worry. 48 V is phantom power...

Just plug them into the Roland, switch the phantom power on and go.
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Old 09-03-2018, 12:53 AM   #3
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Many people say it is unwise to use phantom power on ribbon mics. I have also seen some videos sceptical of this but probably best to err on the side of caution.

This may also be of use:
https://www.okclips.net/video/DZ5Ady...er-how-to.html
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Old 09-03-2018, 03:22 AM   #4
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It's only dangerous if combined with a defective cable, or with very old vintage ribbon mics that are transformerless. You won't find to many of those around.

And even putting 48V on a transformer will magnetize it a very little bit, worsening the produced noise. But you'd have to plug it several hundred times before it turns into a real problem.
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Old 09-03-2018, 09:46 AM   #5
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It is sometimes said that one should turn phantom on/off while the mic(s) are plugged in, as opposed to plugging them in or pulling the plug while phantom is on.

But this is apparently another "not an issue for modern mics" thing. Most people on this forum (myself included) have plugged in and unplugged hundreds/thousands of mics with phantom enabled without issue.

Enjoy the new mics!

Edit: also be aware that phantom power is invisible to dynamic mics, etc., so you don't have to worry about that.
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Old 09-03-2018, 10:45 AM   #6
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Quote:
I know they need 48V to operate but I'd like to understand the difference between 48V and 48V phantom power.
Yeah... "Phantom" refers to the way it's wired. On the XLR connector pin 1 is ground (and the shield) and the signal is differential on pins 3 & 3.

That is, the signal is taken as an AC voltage difference between 2 & 3, not referenced to ground.

DC Phantom power is applied to both pins 2 & 3, referenced to ground. If you measure the voltage between pins 2 & 3 you won't measure the phantom voltage and the preamp doesn't see it either.

You CAN get into trouble mixing & matching adapters, especially if you adapt to an unbalanced connection.

I'd GUESS most modern XLR mics are "protected" against miswiring, but that protection circuit could potentially fry the 48V power supply, although I'd GUESS it's also short-circuit protected.

Last edited by DVDdoug; 09-03-2018 at 10:50 AM.
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Old 09-03-2018, 11:50 AM   #7
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I plug my guitar pedals via TRS > XLR > interface mic inputs. Last week I played a gig and couldn't figure out why none of the pedals seemed to be working correctly.



Phantom power was on!


Luckily, nothing burned.


Well, except when my friend plugged a 9VAC adapter into a 9VDC pedal, but that was his, and not my fault.
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Old 09-03-2018, 12:00 PM   #8
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Quote:
Originally Posted by ashcat_lt View Post
Luckily, nothing burned.
If anyone is interested, here's a little tester I made (with copious amounts of help, maybe even from ashcat?) to detect power on an XLR jack.
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Old 09-03-2018, 12:50 PM   #9
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Quote:
Originally Posted by DVDdoug View Post
Yeah... "Phantom" refers to the way it's wired. On the XLR connector pin 1 is ground (and the shield) and the signal is differential on pins 3 & 3.

That is, the signal is taken as an AC voltage difference between 2 & 3, not referenced to ground.

DC Phantom power is applied to both pins 2 & 3, referenced to ground. If you measure the voltage between pins 2 & 3 you won't measure the phantom voltage and the preamp doesn't see it either.

You CAN get into trouble mixing & matching adapters, especially if you adapt to an unbalanced connection.

I'd GUESS most modern XLR mics are "protected" against miswiring, but that protection circuit could potentially fry the 48V power supply, although I'd GUESS it's also short-circuit protected.
There's no real protection needed. Max. current is 10 mA, not enough to damage most mics, except, perhaps, transformerless ribbons with a very low impedance and a narrow ribbon. But even that is unlikely. And these are extremely rare. Vintage ribbons all have transformers.

In theory, electrolytic caps in a condenser mic could blow while plugging in with phantom power on if they're specced far below 48V. But even that is extremely unlikely, as the voltage will drop immediately due to the current flow. There might be a zener diode in the mic, dropping the voltage to 12V, but that's not as much for protection as it is for voltage stabilization. Otherwise, the condenser mic might sound completely different on a system with 24V phantom power. Some provide even 12V or 15V phantom power.

On the preamp side, there's a 6,81 kOhm resistor in each leg. And on the mic side there's another resistor in each leg. Around 10 kOhm total. Hence, max. current is around 10 mA.

The only danger in real life is to the plugs, if you use jack plugs. These will provide a short circuit when plugging in or out and might damage something because a charged cap inside the preamp might unload. And the short is on pin 1 first and then on pin 2.

Won't happen if you follow the rule to switch off phantom power before plugging or unplugging anything. And if you're really careful, you'll switch off all power before plugging or unplugging...

And you really shouldn't use jacks for mic signals.

I've seen mics blown because of phantom power when the resistors go short circuit. Fortunately, most resistors go open circuit when blowing up. In very well-made mixers, a type of resistor is used that should always go open circuit when failing.

Having a mic struck by lightning is far more likely than having it damaged by phantom power. And it far more damaging, taking everything out.

Also, don't underestimate current in ground loops. I see gear damaged by fools lifting mains ground at least once a year and I've lost a dear friend because of such fools. Losing a mic is one thing. Losing your life is still a lot worse.
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Old 09-03-2018, 01:16 PM   #10
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Originally Posted by cyrano View Post
Also, don't underestimate current in ground loops. I see gear damaged by fools lifting mains ground at least once a year and I've lost a dear friend because of such fools. Losing a mic is one thing. Losing your life is still a lot worse.
I don't know if you're comfortable talking about it, but if you are I wouldn't mind hearing the story of how your friend lost their life, for the sake of all our safety consciousness.
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Old 09-04-2018, 01:57 AM   #11
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I don't mind. And if it can make some people think about it, it might do some good.

It was during a big festival in Ghent, the "Gentse Feesten". Over 20 years ago.

He was rigging light, up on a ladder. All power was off at the main switch. The main power box had a ground current tripper, so it should have been safe.

Unfortunately, someone needed to operate a drill. And he had pulled a wire from the cellar of a nearby café. That cable was worn and that one wallplug in the cellar had no ground. Somehow, the electricity got into the rigging. And since there was no safety ground, it ran through his right arm and the ladder into ground when he touched it. He died on the spot.

We still miss Geert.
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Old 09-04-2018, 08:19 AM   #12
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My condolences.

Sounds like a pretty classic case. It's amazing to me how careless and casual people can be around electricity; outlets sparking and arcing; 27 things plugged in to one outlet and half hanging out; crappy home wiring jobs.

I've told this story here before, but: a friend had a stove that I shocked myself on (my forehead! I was working on something on the range top and leaned my forehead against the fan hood above the stove.) Some clueless person (previous owner) had piggybacked the 120V circuit for the fan hood light off the 240V circuit for the range, but had done it wrong, and had connected the hood itself to mains current instead of ground. The stove had been infamous for years in their house for shocking people. Yikes. (I fixed it for them.)
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Old 09-04-2018, 08:48 AM   #13
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Many barefooted musicians died on stage, often zapped trough the mic's metal grid.

I've been shocked once by touching my bass's strings and the guitar player at the same time, and another time I had to rehearse on a chair with my feet off the ground the whole evening because I was barefooted and I could feel the current as I touched the strings. I didn't die, but I felt really stupid. Then I disconnected the strings from the ground on my basses and guitars. Now I cringe when I see Steven Wilson live.
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Old 09-06-2018, 09:00 PM   #14
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Quote:
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Don't worry. 48 V is phantom power...

Just plug them into the Roland, switch the phantom power on and go.
Thanks cyrano and all the rest of you guys for your help!
I appreciate it.
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