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.
Original Post
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)
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?
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
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
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
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
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
Mike,

I *may* still have an outboard phantom power supply kicking around here someplace. If I do I'll check the voltage and if it is 48V, I'll try to do some listening tests.

That's a lot of ifs but if there is anything to report, I will.
quote:
Originally posted by Mike in Texas:
Yes, Hilmar - thanks...

What's the price tag on this thing?


I coulnd't find a price online, but I expect it's rather expensive as their tube power supplies are more than $1000.
Typical single or dual channel 48V phantom supplies cost somewhere between $25 and $100.
I am not qualified to talk tech on this or any other mic, perhaps a look at the KMS 105 manual would help someone to know if there is a design feature that would make a difference.

The manual states in a couple of places that the KMS105 needs a "minimum" or "at least" 3.5 mA. (If I remember correctly, I don't have it with me here.)

It also describes the phantom voltage as being split evenly across two resistors and returned by the shield, or something to that effect. Whether or not that is a "normal" condenser circuit I really don't know.

I wholeheartedly agree with Hilmar that the comparison I am making, even though it is not my intention to influence the sound with the mixer, is not apples to apples, and is purely subjective until proven differently, which is not my intention either.

Mike, the power supply I was referring to is a simple 48v unit for one mic about $70 retail I think, they have another for either 4 or maybe six mics that is under $300. Again I am not looking at the info so I may not be exact. It is not the same as Hilmar linked to.

ST, I have a Yamaha 2816 DAW with onboard mixer that is similar to the O1V, I have not used the Neumann with that for live or recording.

There is no doubt in my mind that there is a difference when using the KMS 105 direct vs. through the mixer, and I might add that I don't notice a difference if I am using my EV 767 mic in a similar way.

This is not intended to knock either the Neumann mic or the PAS, just a subjective observation.

The Neumann mic has made me deal with proximity effect all over again, something that is not so noticable with the EV's I have been using. I have been thinking about that and will share some of those thoughts in a few days in another thread.

MTM, I have taken a day job that does curtail my time with the PAS and guitar, but I still try to play a little every day. Work is really overrated, I'm not sure how I fell for this but after two years of vacation my wife was getting a little edgy, maybe because she was working for those two years!!

Oldghm
quote:
Originally posted by MTM:
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


Good point. I stand corrected. It would be nice if we could get some momentum going on a single standard; it would be nice for consumers to not have to think about it. Kinda like how USB periperhals and computer monitors are super easy to deal with now.

Thanks Mike,
Steve
Hi Robert L,

You must have been bored, and up late to revive this old thread.

Not unhappy at all with the EV's. I was ordering some additional EV 767a's, and I guess I had too much money laying around, and all the talk on this forum about how good the 105 is, made me do it.

It (the 105) is a good mic, but hasn't yet, and is not likely to, replace my 767a for my live work.

While one could argue that the KMS105 is far superior to the EV 767a, it just doesn't "do it" for me.

The next time I do some home recording I plan to try it with the DAW, maybe I'll like it better in that type of use. Maybe not.

I'm currently curious about the Sennheiser E935 and E945 mics. One was donated for comparison (E935) in a demonstration I did at the Ashland conference. I was impressed, and am thinking about buying me one for Christmas.

Oldghm
I today bought the 105 mic after reading reviews on this site. There was only the slightest difference between it and the shure beta 87a mic and the 105 was twice the price here in Ireland.
I now probably wish I had bought the shure and used the extra money on something else. Both mics where better than my Beyerdynamic TGX60.
The shop also let me take a trial of the studio master C3X mixer which is a 1U rack mixer with FX but the Phantom power switch says +17v instead of 48v so I am wondering will this suit my mic?
Damien,

It is very hard to be objective about vocal mics. Each one of us has a unique voice and delivery. That means that the sometimes subtle differences in mics will shine for one person and not for another. If you like your mic and it is working for you don't let another's opinion make you question your decision.

On the other hand if you feel you made the wrong decision after a short use at home, and think the Shure will do the job just as well, maybe they will trade back. In my area, some of the local stores won't give a refund, but they will give in store credit on returns, and we always need something else sooner or later.

The mics I mentioned above are all very good. In the US the EV is under $130 and the Sennheisers are currently advertised at $159 for the 935 and $199 for the 945, these are dynamic mics and require no phantom power.

Not sure about the 17 volt phantom, but I don't think it will hurt to give it a try.

O
quote:
the Phantom power switch says +17v instead of 48v so I am wondering will this suit my mic?


If you have a 6 volt flashlight and the batteries are only putting out 3 volts the bulb will still light. You would have to say that the flashlight will operate on only 3 volts but I'm sure you would notice a difference in performance.


Robert L

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