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Author Topic: A quandry from the Mackie manual.  (Read 7759 times)

Ian Stuart

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Re: A quandry from the Mackie manual.
« Reply #10 on: April 18, 2011, 08:16:33 am »

Whether you are wondering or not, Phantom power is NOT applied to pin 1. +48V phantom supply voltage is applied to both pins 2 and 3 through separate 6.81k resistors. Pin 1 is connected to ground to return the phantom power current back from the mic circuitry to the console power supply.

JR

Who cares? Do I build consoles, preamps and/or microphones? No. The point that I wanted to make was that the 48v positive is applied to one pin which is most commonly separate from any TRS jacks. I feel that it makes little difference to OP anyway. Sorry if I offended with my "Industrial Stupidity"... Wankers.
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Mac Kerr

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Correcting wrong information
« Reply #11 on: April 18, 2011, 11:10:10 am »

Who cares? Do I build consoles, preamps and/or microphones? No. The point that I wanted to make was that the 48v positive is applied to one pin which is most commonly separate from any TRS jacks. I feel that it makes little difference to OP anyway. Sorry if I offended with my "Industrial Stupidity"... Wankers.

You got corrected because what you posted was completely wrong. In these forums the difference between correct and incorrect information actually matters. Sorry if that offends you.

Mac
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John Roberts {JR}

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Re: A quandry from the Mackie manual.
« Reply #12 on: April 18, 2011, 11:11:53 am »

Whether you are wondering or not, Phantom power is NOT applied to pin 1. +48V phantom supply voltage is applied to both pins 2 and 3 through separate 6.81k resistors. Pin 1 is connected to ground to return the phantom power current back from the mic circuitry to the console power supply.

JR

Who cares? Do I build consoles, preamps and/or microphones? No. The point that I wanted to make was that the 48v positive is applied to one pin which is most commonly separate from any TRS jacks. I feel that it makes little difference to OP anyway. Sorry if I offended with my "Industrial Stupidity"... Wankers.

I for one, care about the accuracy of answers. Many people don't know and look to forums like this for information.

In this case how phantom power is connected actually matters, because it explains the unusual circumstance, that how the microphone is wired matters in the context of phantom supply.

Phantom power is applied common mode, to both pins 2 and 3. As long as the microphone is wired balanced, the voltage is the same at pins 2 and 3, so no current flows inside the dynamic mic. If one leg of the mic is grounded, the phantom current flows through the mic.

JR

PS I have no explanation for the Alto unit that self destructs one input at a time when global phantom is applied to a dynamic mic. Clearly a faulty design. 
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Dave Potter

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Re: A quandry from the Mackie manual.
« Reply #13 on: April 18, 2011, 01:44:30 pm »

Quote
PS I have no explanation for the Alto unit that self destructs one input at a time when global phantom is applied to a dynamic mic. Clearly a faulty design.

Or a faulty mic transformer and whimpy resistors on the phantom channels.

Anyway;  Enough is enough.  Lets walk away from the arguments and get on with important things........ Will phantom power run my toothbrush?....... ;)
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Greg_Cameron

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Re: A quandry from the Mackie manual.
« Reply #14 on: April 18, 2011, 02:28:40 pm »

I can't think of any modern mics that would be unbalanced AND XLR, but I suppose they need to cover the basses.

Since the world is full of adapters of pretty much every conceivable configuration combined with operators that know little to nothing about audio or electronics, someone is bound to do it wrong. And this is one case where it's not tough to conceive. Let's say you have one of these Rat Shack beauties here:



And let say you just bought yourself one of them fancy Midas XL88s because you have a new hobby called "PA" for doing back yard parties and such and all ready have this cool top notch mic you got from Rat Shack 30 years ago and you want to do some karaoke. So you get yourself one of these from the local Bango Center:



Then you go ahead and flip on the phantom power for that channel 'cause "if it's 'phantom power,' that will make things more powerful."

And then there's a problem.

Greg

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John Roberts {JR}

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Re: A quandry from the Mackie manual.
« Reply #15 on: April 18, 2011, 04:39:20 pm »

Quote
PS I have no explanation for the Alto unit that self destructs one input at a time when global phantom is applied to a dynamic mic. Clearly a faulty design.

Or a faulty mic transformer and whimpy resistors on the phantom channels.

Anyway;  Enough is enough.  Lets walk away from the arguments and get on with important things........ Will phantom power run my toothbrush?....... ;)

I didn't know this was an argument.

I guess it is possible to find resistors small enough that they are technically overloaded by 1/3W, but even if they burned up (they won't), that channel would probably still work with not phantom mics.

Not even sure how transformers could be bad that could break stuff.
========
yes, phantom power probably does provide enough current to run your electric toothbrush. If not enough to run it full time, surely enough to charge it up.
-------

Thinking about this a little more, I have a theory and a question for Kristian. Were those mics with one input leg shorted, plugged in "after" global phantom power was turned on. That could make a big difference.

If yes, that shorted input to ground, was driving the phantom DC blocking cap that was sitting fully charged up to 48V, down to ground in an instant. When that happened, the other end of that cap that was sitting at roughly 0V, was instantly driven to -48V. Since the mic input circuitry can't go to -48V when operated from only a -15V supply, something has to give.

Good design practice is to provide clamp circuitry to absorb such transient currents that could amount to several amps (depending on blocking cap size and ESR). These momentary shorts are more common in large recording studios with patch bays, so professional recording inputs are well protected, I suspect the Alto had inadequate protection for this user fault, if any protection at all.

BTW, it always good practice to "not" hot plug mics in with phantom power on, for this very reason.

Maybe now I'll walk away...

JR 
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Ian Stuart

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Re: Correcting wrong information
« Reply #16 on: April 18, 2011, 11:19:44 pm »

You got corrected because what you posted was completely wrong. In these forums the difference between correct and incorrect information actually matters. Sorry if that offends you.

Mac

It doesn't offend me at all Mac, what offends me is the presentation of said correction. There is a tactful way of correcting someone and labeling my post 'stupidity' is not a tactful way of doing that.

I appreciate that my knowledge has been challenged and I learnt something from this today, I also take back what I said about not caring. However I don't deserve to be called stupid because I accidentally slipped the wrong information whilst trying to be helpful to the OP.
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Greg_Cameron

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Re: Correcting wrong information
« Reply #17 on: April 18, 2011, 11:43:55 pm »

However I don't deserve to be called stupid because I accidentally slipped the wrong information whilst trying to be helpful to the OP.

I read through the thread. I didn't see anyone call your post stupid, just incorrect.

Greg

[edit: corrected context]
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Adam Wh3tham

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Re: Correcting wrong information
« Reply #18 on: April 19, 2011, 12:15:54 am »

However I don't deserve to be called stupid because I accidentally slipped the wrong information whilst trying to be helpful to the OP.

I read through the thread. I didn't see anyone call your post stupid, just incorrect.

Greg

[edit: corrected context]

+1 didn't see a stupid from JR or anyone. Tuff love. Get used to it.
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kristianjohnsen

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Re: A quandry from the Mackie manual.
« Reply #19 on: April 19, 2011, 09:12:32 am »

Quote
PS I have no explanation for the Alto unit that self destructs one input at a time when global phantom is applied to a dynamic mic. Clearly a faulty design.

Or a faulty mic transformer and whimpy resistors on the phantom channels.

Anyway;  Enough is enough.  Lets walk away from the arguments and get on with important things........ Will phantom power run my toothbrush?....... ;)

I didn't know this was an argument.

I guess it is possible to find resistors small enough that they are technically overloaded by 1/3W, but even if they burned up (they won't), that channel would probably still work with not phantom mics.

Not even sure how transformers could be bad that could break stuff.
========
yes, phantom power probably does provide enough current to run your electric toothbrush. If not enough to run it full time, surely enough to charge it up.
-------

Thinking about this a little more, I have a theory and a question for Kristian. Were those mics with one input leg shorted, plugged in "after" global phantom power was turned on. That could make a big difference.

If yes, that shorted input to ground, was driving the phantom DC blocking cap that was sitting fully charged up to 48V, down to ground in an instant. When that happened, the other end of that cap that was sitting at roughly 0V, was instantly driven to -48V. Since the mic input circuitry can't go to -48V when operated from only a -15V supply, something has to give.

Good design practice is to provide clamp circuitry to absorb such transient currents that could amount to several amps (depending on blocking cap size and ESR). These momentary shorts are more common in large recording studios with patch bays, so professional recording inputs are well protected, I suspect the Alto had inadequate protection for this user fault, if any protection at all.

BTW, it always good practice to "not" hot plug mics in with phantom power on, for this very reason.

Maybe now I'll walk away...

JR

Unfortunately, I have a hard time recalling the details on this one - but if I had to guess I would say that the mics were plugged in while phantom power was switched on.

Thanks for your insight! :)
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ProSoundWeb Community

Re: A quandry from the Mackie manual.
« Reply #19 on: April 19, 2011, 09:12:32 am »


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