Highlighted
Member
  • 0
  • 161
  • 0
Registered since

Dec 13, 2005

Phantom power

Howdy, all.
The other night at a gig, as I powered everything up I noticed the LED's on my mixer's DB meter were on. Nothing was plugged in and all mains were down. I quickly found I had accidentaly hit the phantom power button on the PAS ch.1. Eek
My question is, What, if any, damage could be done to either the mixer or ,more importantly, the PAS ? Everything appears to be working normally. I just want to be sure.
Thanks.
24 REPLIES 24
Highlighted
Member
  • 0
  • 1
  • 0
Registered since

Feb 14, 2006

Re: Phantom power

SEPARATE PHANTOM ISSUE:
why is it only 24v? the top mics (i.e. my neumanns) need all the 'standard' 48v to operate. i am not a pro-sumer, i need the phantom to be 48v. please develop a mod :O)
Highlighted
Professional Legend
  • 1412
  • 48121
  • 1
Registered since

May 11, 2020

Re: Phantom power

Hi aspie,

There is a discussion about this Bose Phantom Power Issue. It includes references and technical notes.

All of my Neumanns work fine with the Bose System (KMS 105, KM 184, U87, TLM 103).

Are you having an issue with a specific microphone (or have one in mind)?



quote:
Originally posted by aspie:
SEPARATE PHANTOM ISSUE:
why is it only 24v? the top mics (i.e. my neumanns) need all the 'standard' 48v to operate. i am not a pro-sumer, i need the phantom to be 48v. please develop a mod :O)
Highlighted
Professional Legend
  • 1412
  • 48121
  • 1
Registered since

May 11, 2020

Re: Phantom power

Hi Strat man

quote:
Originally posted by Strat man:
Howdy, all.
The other night at a gig, as I powered everything up I noticed the LED's on my mixer's DB meter were on. Nothing was plugged in and all mains were down. I quickly found I had accidentaly hit the phantom power button on the PAS ch.1. Eek
My question is, What, if any, damage could be done to either the mixer or ,more importantly, the PAS ? Everything appears to be working normally. I just want to be sure.
Thanks.


If everything is still working, then you're probably fine.

Out of curiousity, what kind of mixer are you using. Does it say anything in the documentation about protection on the balanced outs?
Highlighted
Member
  • 0
  • 161
  • 0
Registered since

Dec 13, 2005

Re: Phantom power

Hey ST,
I forgot about this post !!
Everthing is working fine
The mixer is a Mackie cfx12mk11 and the manual dosen't say anything about protection.

Thanks
Highlighted
Member
  • 1
  • 2306
  • 0
Registered since

Oct 2, 2003

Re: Phantom power

quote:
Originally posted by aspie:
SEPARATE PHANTOM ISSUE:
why is it only 24v? the top mics (i.e. my neumanns) need all the 'standard' 48v to operate. i am not a pro-sumer, i need the phantom to be 48v. please develop a mod :O)


Aspie,

Do they "need" 48V or do they specify it? Very few mics need 48V and will work with the international 24V standard (see ST's link above).

I hope that helps,
Steve
Highlighted
Member
  • 0
  • 251
  • 0
Registered since

Aug 26, 2005

Re: Phantom power

quote:

Originally posted by Steve-at-Bose:
...will work with the international 24V standard....


I would liked to reiterate that the "international standard" referred to is nothing more than a suggestion. Please do not make it out to be more than it is.

The de facto "International Standard" is 48 volts.

Mike
Highlighted
Advisor
  • 139
  • 3511
  • 3
Registered since

May 25, 2004

Re: Phantom power

I have questioned in the past, and read all the posts about why mics that are sold with the mfg. specs. 48vdc + or - 4v don't really need 48 volts, and up to a few days ago didn't really question the Bose response because I wasn't attempting to use a mic with those specs.

I recently purchased a KMS 105 and have spent several rehearsal hours with it. I am not ready to say that it doesn't work as well with 24v as it does with 48v, but I will say I don't like it as well straight into the PS1 as I do when I run to my Alesis (48v) then to the PS1.

I am not using mixer EQ, and I am attempting to get the gain as nearly the same from one setup to the other as is possible.

I am currently considering buying the Neumann power supply, but will continue to rehearse for a while because I am not sure I want to use the Neumann for my gigs anyway.

It is hard to describe the difference between the setups, but it seems the mic is more responsive to subtle nuance, or there is an increase in the dynamics when used with 48v.

The "feel" that I get, with the mixer in place, has thus far not been attainable when direct into the PS1.

I suspect there is a difference in "working with 24v." and "working as designed". To get the very best performance from a high quality condenser mic, the separate power supply might be the way to go.

Like some other aspects of the PAS design this is one that will affect only a very small percentage of users / buyers as most will opt for mics that cost less, and are more durable.

Oldghm
Highlighted
Member
  • 0
  • 251
  • 0
Registered since

Aug 26, 2005

Re: Phantom power

quote:

Originally posted by Oldghm:
I am not ready to say that it doesn't work as well with 24v as it does with 48v, but I will say I don't like it as well straight into the PS1 as I do when I run to my Alesis (48v) then to the PS1.

It is hard to describe the difference between the setups, but it seems the mic is more responsive to subtle nuance, or there is an increase in the dynamics when used with 48v.

The "feel" that I get, with the mixer in place, has thus far not been attainable when direct into the PS1.

I suspect there is a difference in "working with 24v." and "working as designed".


Wow.

This is a very interesting observation. Theoretically, the difference in voltage should only make a difference in the maximum SPL that the mic can handle.

However, I have previously opined that 130V DPA mics sound better than their otherwise identical 48V cousins under circumstances where the maximum SPLs they are "listening" to are no where near the limit.

If I had to bet, I would have bet that the PAS preamp would blow away the Alesis, voltage differences notwithstanding. Since I know that you are a careful listener, and not about to jump on any bandwagons unless it is a bandwagon that has met your approval, I don't know what to think.

Do channels 1 and 2 on your PAS sound the same? Does it sound as good as it used to? (I'm wondering if you might have uncovered a service issue?) Do you have access to any other preamps, maybe even some "zooty" recording studio ones to do some comparisons? I know you have oodles of free time for experimenting and reporting to the group. Smile

I'm interested to hear what the -at-Bose folks might think about this.

Mike
Highlighted
Member
  • 0
  • 985
  • 0
Registered since

Oct 13, 2003

Re: Phantom power

That is a somewhat difficult topic. We certainly have tried a KMS105 for live and even for recording with our 24V phantom supply and didn't find any problems. Then again, everybody's ears and taste is a little different, so I can't claim that there really isn't any difference.
Going through the Alesis might also change things a little, so it's hard to do an exact apples-to-apples comparison.

From a technical stand-point, it's difficult for me to believe that there are any issues. I haven't taken a KMS 105 apart yet (they ain't cheap !) but most Neuman mics use an internal DC to DC converter and polarize at 200V or so. If any, that should work better with a "proper" 24 V supply because it can provide nearly twice the overall power of a standard 48V supply. Getting more useable DC power was actually one of the reasons why the 24V standard was suggested.

Different microphones do different things with Phantom Power but it's not only the voltage that matters but also the current. The original 48V/6.8kOhm standard was optimized for microphones that needed external polarization and therefore high voltage but nearly no current at all. But this type of microphone is exceedingly rare these days and the phantom power is used either to drive an internal pre-amp or to run an internal voltage-converter or stabilizer. For both cases a supply with lower voltage and higher current (and more overall power) is actually better and hence the 24V/1.2kOhm standard was derived.

I hope I don't bore everybody to death with some math, but let's look at the example of the KMS105. I believe that at nominal 48 V the mic draws about 4mA. That current also goes through the internal 6.8k Ohm resistor of the phantom power supply and leads to voltage "sag". If we use Ohm's law we find that the internal effective resistance of the microphone is about 5 kOhms and that the voltage at the microphone terminals is only 20 V. All the rest is lost inside the supply. If you attach the same microphone to 24V/1.2kOhm supply the voltage sag is much less and the voltage at the microphone terminals comes out to be 19V. It's hard for me to believe that this 1 V difference should make any apprectiable difference in the mics performance.

For an even more power hungry microphone that draws 5mA, the 24V/1.2kOhm supply will actually provide 3 Volts MORE (17V vs. 14V) at the microphone terminals. Sounds a little counterintuitive, but is actually true.

Of course, in the end you have to be the judge of what sounds best to you ears.

Hope that helps

Hilmar