ProSoundWeb Community
Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => The Basement => Topic started by: Helge A Bentsen on November 23, 2017, 12:59:59 PM
-
Someone told me today that one major difference between various digital mixing consoles is the quality of phantom power. The argument was that some desks had dirty phantom power resulting in more noise and lower quality sound in the higher frequencies on powered sources.
I've never heard about this in the past.
Is there such a thing as dirty phantom power?
Is there a reasonable explanation for why this is/is not an issue?
-
Someone told me today that one major difference between various digital mixing consoles is the quality of phantom power. The argument was that some desks had dirty phantom power resulting in more noise and lower quality sound in the higher frequencies on powered sources.
I've never heard about this in the past.
Is there such a thing as dirty phantom power?
Is there a reasonable explanation for why this is/is not an issue?
I am at a loss as to explain why someone would come up with "dirty phantom power"
It's nothing special. Just 48Vdc from the power supply.
Possibly, there might be a bad capacitor or some other defect in a specific console power supply but I have never heard of , or experienced, any "bad" phantom power.
Anyone else?
-
The phantom power is part of the analog side of the A/D converter. Considering the price point in which 90% of digital mixers will fall in and the relatively high quality of modern A/D - D/A converters, there is a high probability that they will be of good quality and not be of detriment to the consoles design. I have never heard of or experienced " dirty " phantom power. I have had cables that made using phantom power a problem, but swap the cable and all is good. I have had mics go bad that wouldn't work right no matter what powered them.
Phantom power is as old as mixer technology is and the circuit design is pretty much perfected at this point in time. The likelihood that there is a bad circuit design in any modern mixer would be a far fetch. it is not a particularly difficult circuit any way. Now that does not mean that the circuit is infallible and not subject to failure. I am sure that there are more than a few mixers that have had a part within the phantom power circuit fail and cause issues. I would say that under normal operation, there is no inherently bad phantom power supplies in any modern mixer.
-
Someone told me today that one major difference between various digital mixing consoles is the quality of phantom power. The argument was that some desks had dirty phantom power resulting in more noise and lower quality sound in the higher frequencies on powered sources.
I've never heard about this in the past.
Is there such a thing as dirty phantom power?
Is there a reasonable explanation for why this is/is not an issue?
Maybe find somebody else to listen to. ;D
Some people make a living inventing differences when none exists. ::)
There is nothing about a digital mixer that suggests phantom power would be any different.
JR
-
Maybe find somebody else to listen to. ;D
Some people make a living inventing differences when none exists. ::)
There is nothing about a digital mixer that suggests phantom power would be any different.
JR
Maybe the phantom power needs an external clock! ;D ;D
-
Maybe the phantom power needs an external clock! ;D ;D
Or a "hum eliminator" YEAH-that will get rid of the noise-and the signal---------
-
Or a "hum eliminator" YEAH-that will get rid of the noise-and the signal---------
hhhmmmmmmmmmmmm ! now you got me thinkin !
http://www.youtube.com/watch?v=SKRma7PDW10
-
I am at a loss as to explain why someone would come up with "dirty phantom power"
It's nothing special. Just 48Vdc from the power supply.
Possibly, there might be a bad capacitor or some other defect in a specific console power supply but I have never heard of , or experienced, any "bad" phantom power.
Anyone else?
I owned a very cheap Behringer 4 mic pre analog mixer that had "normal" noise and distortion levels with dynamic microphones, but had a peculiar "whining" noise using the phantom power with condenser mics. The phantom power was a global switch, it did not cause noise in the dynamic mics, but the noise varied between different types of condenser microphones, the "true condensers" were different than the back electrets. Using the same mics and cords, the noise was absent using other mixers, or a little two channel phantom power supply, (which cost as much as the mixer..).
Considering the cost of the mixer, and how it generally was not used with condenser mics, I never pursued the cause of the problem, but it definitely provided "bad" phantom power. A quick check would not reveal the problem- if you were listening in a noisy room you would not notice the weird noise. This mixer was from the late 1990's before Behringer was doing most of their own manufacturing, I suspect it's "wall wart" power supply may have been re-supplied and varied in some way from the original design specification.
Never have experienced "bad phantom" power on any other mixers, but once was enough to know it is possible, even if I don't know exactly what caused it.
Art
-
Since I am a silly old git in forum land I have 1 question.
Don't you just hate it when a superhero goes bad?
-
Never have experienced "bad phantom" power on any other mixers, but once was enough to know it is possible, even if I don't know exactly what caused it.
Art
That does not remotely support the thesis that some digital mixers have dirty phantom power. Only that old cheap small Behringer mixers could (did once).
FWIW there are multiple factors that influence the likelihood of phantom power related noise...
Since competent preamp designs reject common mode noise it isn't linear with the actual 48V noise. Further a squirrely mic (or cable) could imbalance the input impedances degrading CM rejection of even a well designed preamp.
JR
-
Someone told me today that one major difference between various digital mixing consoles is the quality of phantom power. The argument was that some desks had dirty phantom power resulting in more noise and lower quality sound in the higher frequencies on powered sources.
I've never heard about this in the past.
Is there such a thing as dirty phantom power?
Is there a reasonable explanation for why this is/is not an issue?
I don't know about "dirty". but what make sense is, that some consoles have one 48V phantom power supply (even if you have separate select button on every channel. the source is still one power supply) with NOT enough Va on the transformer. causing it to drop voltage as you add microphones or active DI. which will reduce the quality of the Mic/Preamp. Or to begin with, they are not 48V.
Other consoles have separate power (Transformers) for every channel. not causing to drop voltage as you add phantom.
This can be measured with a volt meter.
i hope that helps.
Yoel Farkas
-
I don't know about "dirty". but what make sense is, that some consoles have one 48V phantom power supply (even if you have separate select button on every channel. the source is still one power supply) with NOT enough Va on the transformer. causing it to drop voltage as you add microphones or active DI. which will reduce the quality of the Mic/Preamp. Or to begin with, they are not 48V.
Other consoles have separate power (Transformers) for every channel. not causing to drop voltage as you add phantom.
This can be measured with a volt meter.
i hope that helps.
Yoel Farkas
And it could be that the phantom power is not 48V. A number of cheaper consoles use a lower phantom voltage. I have seen 24 and 12V.
It could be that the mics in question need 48V and don't work well with a lower voltage.
-
The soundcraft ui 12-16 (not the 24i) have been reported to have excessive noise when +48 was engadged.
-
The soundcraft ui 12-16 (not the 24i) have been reported to have excessive noise when +48 was engadged.
that seams to be another issue with grounding of the transformer.
lack of voltage will degrade the quality of the sound and it should not induce noise. if i'm correct.
Yoel Farkas
-
Seriously... how many consoles have you guys designed...?
Hope my comments helped.
JR
-
Seriously... how many consoles have you guys designed...?
Hope my comments helped.
JR
I had never designed a console. i took that information from one of the AES sessions i attend. i think it was Bill Whitlock from Jensan Transformers. he measure consoles voltage. as far as Voltage supply and Shielding of the console. and he find some consoles drop on voltage as you add phantom power use. and some even doesn't provide 48V to begin with.
Yoel Farkas.
-
I had never designed a console. i took that information from one of the AES sessions i attend. i think it was Bill Whitlock from Jensan Transformers. he measure consoles voltage. as far as Voltage supply and Shielding of the console. and he find some consoles drop on voltage as you add phantom power use. and some even doesn't provide 48V to begin with.
Yoel Farkas.
Many phantom voltage mics work fine all the way down to 9V.... There are even accessory phantom PS that use 9V batteries.
Sorry... I spent decades in the trenches, there are a number of factors other than the actual voltage.
JR
-
Many phantom voltage mics work fine all the way down to 9V.... There are even accessory phantom PS that use 9V batteries.
Sorry... I spent decades in the trenches, there are a number of factors other than the actual voltage.
JR
Which is what I was about to post JR. Low phantom voltage MAY decrease sensitivity, but even that is doubtful. "Dirty phantom power could only be described as being dirty if there is an A/C voltage present. This could only occur if the power supply is not designed to provide proper rectification or filtering of the incoming A/C. In todays world 48v phantom power is no more than a figure and many, many boards produce far less than a true usable 48v. Also, one or many separate supplies for phantom power will make no difference considering that most mics requiring phantom power will draw less than 50ma.
In addition to the other boards I own I also own a Soundcraft Ui that has been in use for over two years. Like all of the other misstated comments concerning channel noise I'll put the phantom power statement in the same category as the "no headroom" statements that seems to be so popular, especially with people who don't own the board. There is not now, or has there ever been a real problem with the phantom power circuits on the Ui series boards.
Behringer shouldn't be considered when comparing anything to be used for real sound work. Anything could go wrong with a Behringer product at any time for any reason making any case vs Behringer a non subject. Cheap components make for cheap boards.
-
I had never designed a console. i took that information from one of the AES sessions i attend. i think it was Bill Whitlock from Jensan Transformers. he measure consoles voltage. as far as Voltage supply and Shielding of the console. and he find some consoles drop on voltage as you add phantom power use. and some even doesn't provide 48V to begin with.
Yoel Farkas.
To my knowledge Jensen makes audio transformers. I can't imaging a step down transformer for the phantom on each channel. As John pointed out we don't design consoles but I have worked on quite a bit of gear over the years and sending high voltage all over the chassis seems like an impractical design.
-
I don't know about "dirty". but what make sense is, that some consoles have one 48V phantom power supply (even if you have separate select button on every channel. the source is still one power supply) with NOT enough Va on the transformer. causing it to drop voltage as you add microphones or active DI.
As each channel of phantom power can only source about 7mA of current due to the series resistors in the mixer and the input device, that is highly unlikely as even a 32 channel mixer would only require just over 200mA.
And that 7mA figure is for a zero ohm load. If you actually want some voltage to work the mic or DI, you will only want to drop about half that voltage across the resistors, leaving 24v for the circuit, then it's about 100mA for a 32 channel mixer with all channels supplying phantom power, which in itself is an unlikely scenario.
Many phantom voltage mics work fine all the way down to 9V.... There are even accessory phantom PS that use 9V batteries.
As John says, many work at 9v. None actually work at 48v as there is always going to be voltage drop across the resistors. 48v is what is supplied inside the mixer. In the mic or DI, the usable voltage will depend on the current drawn and is more likely to be between 9v and 24v.
Steve.
-
Many phantom voltage mics work fine all the way down to 9V.... There are even accessory phantom PS that use 9V batteries.
That is true!
My Sound Devices location sound mixer runs on 3 AA batts and doesn't supply 48 volts of phantom and the mic sounds just fine.
-
I’ve got an old Mackie Onyx 2 channel interface that gets its phantom power from a home brew DC-DC circuit, running a fair bit above the audible range. Apparently earlier versions of the circuit ran *in* the audible range!
I couldn’t use that phantom power with my MacBook because something in the FireWire connection also had a little bit of very high frequency tone on it, which mixed together with the slight tone on the phantom supply produced an audible difference tone.
Doesn’t take much to be audible in a mic preamp.
-
I’d be curious to know what consoles you’ve encountered that have more than one phantom power supply and even more curious to know which consoles have a separate power transformer for each channel. Does this include separate rectifiers, capacitors and regulators for each channel? I can remember some old consoles the had local regulators for the power supply rails but not complete local phantom supplies.
I don't know about "dirty". but what make sense is, that some consoles have one 48V phantom power supply (even if you have separate select button on every channel. the source is still one power supply) with NOT enough Va on the transformer. causing it to drop voltage as you add microphones or active DI. which will reduce the quality of the Mic/Preamp. Or to begin with, they are not 48V.
Other consoles have separate power (Transformers) for every channel. not causing to drop voltage as you add phantom.
This can be measured with a volt meter.
i hope that helps.
Yoel Farkas
-
I’d be curious to know what consoles you’ve encountered that have more than one phantom power supply and even more curious to know which consoles have a separate power transformer for each channel. Does this include separate rectifiers, capacitors and regulators for each channel? I can remember some old consoles the had local regulators for the power supply rails but not complete local phantom supplies.
Common practice is to use only one phantom PS rail per console, but channels in premium consoles can have individual on/off switches and local RC filtering. Budget consoles routinely use global switch for all channels, and this created problems in the early days of wireless mics when their receivers couldn't handle 48V (modern receivers can).
I’ve got an old Mackie Onyx 2 channel interface that gets its phantom power from a home brew DC-DC circuit, running a fair bit above the audible range. Apparently earlier versions of the circuit ran *in* the audible range!
I couldn’t use that phantom power with my MacBook because something in the FireWire connection also had a little bit of very high frequency tone on it, which mixed together with the slight tone on the phantom supply produced an audible difference tone.
Doesn’t take much to be audible in a mic preamp.
Mic preamps are not all created equal.... more likely a preamp with poor CMRR at HF...
Many preamps will include HF filters in their front end, if those filters on the + and - inputs are not identical, common mode HF noise will not be presented equally to both inputs so won't cancel completely.
I repeat there are multiple factors at play. A good preamp should reject common mode noise on the phantom supply whether it's 120Hz or 100kHz, while 100kHz will be harder to scrub.
JR
-
I repeat there are multiple factors at play. A good preamp should reject common mode noise on the phantom supply whether it's 120Hz or 100kHz, while 100kHz will be harder to scrub.
While I tend to agree that this is tempest in a teapot, I did find this interesting perspective (from roughly 10 years ago): http://repforums.prosoundweb.com/index.php?topic=3361.30
GTD