Some tech representatives from Zennheiser have recommended that I consider using 52 volt phantom power.

Has anyone here have any experience with this extra juice phantom?

with thanks for your help and discussion,

PhlushPhonic

I run my pre around 50 volts. I could make it the Max 52 volts but someone may have a problem with this level.
DB wise it depends on the current the mic draws, 4ma load you end of with around 36 volts, 2ma load it's in the 43 volt range. That's what the mic has to work with...
It also depends on the amp circuit, it may have regulation for better isolation, meaning it takes that 48 volts regulates it down to say 30 volts...
My point is it depends...
Some mics like an older U87 draws very little current, around .5ma, that leaves around 44.6 volts the mic has to work with...
Some mics headroom varies with the phantom voltage, some change very little...

Plush, did they explain WHY?

I've always thought it was about providing enough amperage at 48V that was important, not increasing the voltage. Maybe they know something we should all know.

JvB

The amps is limited by the 6.8K phantom resistors.
And the difference between 48 and 52 volts is less than 1db, output level..

Sounds a bit strange?? Maybe it permits a little more headroom??

How can you change to 48V to 52V???

The phantom standard says 48V plus/minus 4V at the power supply end. After that comes the 6.8k resistors and there is of course a voltage drop over them. In other words, the mics should be able to handle any supply between 44 and 52V without changing behaviour. Why any factory representative would suggest going specifically for 52V goes beyond my understanding. It might be just one more misunderstanding, there seems to be quite a few in this world.

Gunnar

I have one of my Millennia preamps modified with a switch so I can change the phantom ballast resistors from 6.8k to a lower value. This was suggested to me by David Josephson. I have a pair of his Series Six mics that seem to like it.

David L. Rick
Seventh String Recording

what value?
And if its a big difference I would say with out question it would be a BAD idea.

No, it's a good idea, because it makes more current available for the amplifier and bias generator.

In the case of the Josephson mics, the amps do perform better with more current, and do have enough output poop to drive the lower impedance presented by the lower valued phantom resistors.

But it's an operator aware issue, and both David R and David J are aware!

Hudson,
I've modded all our mic preamps to make 52vdc. The Sennheiser's are MUCH happier at 52v, especially at the end of a 300' piece of snake.
CMC-5's also benefit from the extra voltage/current. CMC-6's seem to be pretty immune to the phantom voltage.
All the best,
-mark

I find this very interesting, the C617 mic specs state a 50 ohm output and recommend a greater than 1K load...By the way this is a 20 TIMES higher, not the 10 times...
If you start with a 1200 ohm pre and lower the phantom resistors you also lower the input impedance on the pre...Your so called improving one thing and make the other just as important thing WORST...forget the fact you may fry another mic that's looking for that voltage drop across the 6.8K resistors...
I would suggest if a Mic manufacturer has a problem with the voltage/current phantom presents then they should do what tube mics companies do, BUILD their own supplies...
Or like DPA and their 130volt mics, external supply...
Or look at a few mics like the AT4050 that excell on that 48volts, very high headroom, low impedance...Gee how do they do it????
The Sennheiser MKH-800 also specs a min 1000 ohm load...
Or bump it to the max of 52 volts and forget it...

Are they modded to always deliver 52v, or is it switchable?
Are there any typical orchestral mics you can think of that would be at a disadvantage with 52v?

the bulk of our phantom mics are TLM170, cmc5 and TLM50

All of those mics are spec at 48V +-4 or 52V max.
So 52 would be just fine, WITH the standard 6.8K resistors....

Perhaps the Sennheisers draw on the high end of the allowable current, which means the voltage they actually see through the resistors will be low. Going to the high end of the phantom power spec will get them a little more voltage at the mic, so more headroom.

Keep in mind that the voltage the mic circuitry actually sees is completely dependent on how much current it draws.

Yes, I listed a few numbers to support this.
The MKH-800 draws 3ma, for comparison the AT4050 draws 4.2ma.
Or in voltage drop: MKH-800 10.2 volt drop, leaving a 37.8v
AT-4050 14.28 volt drop, leaving a 33.72v.
A little math to get the day started off right...

I was always told that the CMC's were very current hungry in comparison with other mic amps. Supposedly not much of a problem with a pair or two, however with 20 or so many "smaller" desks of the type favoured by us location engineers a few years ago could struggle. Personally I would have thought that current supply would be more the issue, I would expect that microphone designers would build in a fair amount of lattitude into the design to make sure that their products works optimally under substandard conditions, particularly given the variable nature of budget desk electronics.

Regards


Roland

That's correct - if anybody is scratching their head over those numbers the current is split between the two 6.8k resistors, so the drop is half of what you would expect given the current and one 6.8k resistor.

I have some CAD M179s that draw 8mA, which would give a drop of 27.2V, leaving you with 20.8V for the electronics. That's starting to get kind of low. Of course there are a lot of people here that probably don't consider those real mics anyway.

Thank you much , mic jockies!

Very good and helpful discussion here.
I wasn't sure if an esoteric question like this one would yield any news or discussion.

Thank you, experts. I'm not sure what I'll do, maybe mod one of our mic amps to run at 52V and then I'll listen.

Only on GS could I hope to ever receive this type of help and good suggestions.

Kjetil,
We've found no microphones that are adversely affected by the increase to 52vdc.
The Neumann's typically are very tolerant of sagging phantom and as a class the fet80 and fet100 preamps are on the lower end of current consumption. In the old days we used to run a pair of fet80 mics (km83 and km84) in series on a single channel of phantom power for Volker's "Straus Paket".
The issue with CMC-5's is that they are very current hungry. As the current consumption increases, the voltage drop across the 6.81k resistors increases, the voltage at the mic drops and you get less output from the microphone. Less output means more gain on the preamp and the corresponding increase in noise.........
You can see where this is going. Not a big deal with 2 microphones, but with 20 or 30....
All the best,
-mark

But after very long cable runs the actual voltage is going to end up being lower right?
Thus 52v might be better for safety, so to speak?

huub

I don't think any length of cable run will have any significance compared to the 6.8K resistors feeding it, unless we're talking multiple 1000's of feet of cable.

52V shouldn't hurt anything though, as has been mentioned. It's within the spec. It would seem it can only help. Just don't go higher.

Its the capacitance that adds up and loads the mic...

Yes, which raising the voltage would have no affect on.

USA version:
Imagine asking this same question to an employee at Radioshack??

Europe version:
Imagine asking this same question to an employee at MediaMarket/UniEuro??

On another discussion forum I was told to ignore the 52 volt suggestions because most mics use a DC converter to regulate the P48 power that the mic receives.

We use Schoeps, Senn. MKH series, Neumann 100 series, Pearl among others.

Mics with regulation will not benefit from the higher Phantom voltage---is that right?

thanks,

Phlush

I mentioned this already, if the mic regulates that >38volts down to say 28 volts then no it will make NO difference.
The 48V is also used to polarize the capsule, depending on if the mic bumps that voltage up higher for that purpose then the higher voltage maynot accomplish anything.
It depends on the mic and what they do with that voltage...

Thank you so much Mark!

How big an operation would it be to retrofit a Millennia HV3D to provide 52v?

I dunno, but adding switchable ballast resistors should be pretty easy on any Millennia channel that doesn't have the 130V option -- you've already got a spare switch on the front panel.

Look folks, from the mic's standpoint there's not a heck of a lot of difference between raising the open circuit phantom voltage by 10% and lowering the ballast resistor values by 10%. Both provide the same amount of extra current. [EDIT: For mics with constant-current biasing, see below.] You can lower the ballast resistor value by switching in 68k resistors in parallel with the 6.8k ones that are already there.

David L. Rick
Seventh String Recording

The most difference db wise you could get, from 44 to 52v is 1.5db.
That's it...
I would NEVER change the phantom resistors, this is opening a can of worms that could be worst than the ribbon/phantom issue...
Mics are designed around the voltage drop of those 6.8K resistors, plus like I mentioned it lowers the input impedance....
But it's your choice...

Changing the ballast resistors by 10% is not going to overwhelm the output stage of any competently-designed microphone. Mics already see much greater impedance differences between one preamp and another. For instance, the input impedance of a Millennia preamp is significantly higher than that of many other preamps, and this causes some mics to sound different (for better or worse). There are several other preamps that have selectable input impedance to exploit this effect.

For microphones with constant-current biasing, raising the phantom voltage raises the supply voltage seen by the microphone by an identical amount (4V). Reducing the ballast resistor raises the supply voltage seen by the microphone by a smaller amount. For a microphone drawing 6 mA, the increase is about 2V. If you really want a 4V increase, you could reduce the ballast resistors by 20% (put 34k resistors in parallel). I can't seem to find any record of what I did on the Millennia preamp I use with my Josephson mics, but I did feel it improved the sound.

There's certainly nothing inherently more dangerous about changing the resistance compared with changing the open-circuit voltage. The big advantage of the former is that you can easily have a switch to disconnect the parallel resistors when using a mic that you're concerned about. This should be a very easy modification.

Raising the voltage can be easy or hard depending on the design of the phantom power supply. In the best case, you'd only have to change one resistor, but the new value might be hard to calculate if you don't have full service documentation. In the worst case, you'd have to rewind a power transformer.

David L. Rick