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Thread: Phantom Power for Oktava MK-219 Mic

  1. #11
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    Quote Originally Posted by arcaxis View Post
    Well you got my curiosity up, so I popped the 'hood' on the PS400 so I could make some direct voltage measurements with a few mics at the XLR. (I keep saying I'm going to build a cable jig to do this).

    The operating currents noted are from manufacturers specs. Coincidentally I have a CAD M179 which pulls 8ma like the MK-219.

    MIC, Required current ma, Actual volts measured at PS400 XLR
    AT2020, 2ma, 40.2vdc
    AT3035, 3.5ma, 38.5vdc
    KSM27, 5.4ma, 28.8vdc
    CAD M179, 8ma, 4.52vdc

    Did not try to see if mic was functional or sounded like crap. The voltage drops were reasonable and expected until the CAD M179 was connected. The PS400 power supply just sinks when it sees the 8ma load.

    If the phantom power limiting resistors are the typical 6800 ohms in your UR22, the calculated voltage your MK-219 may actually get at the XLR may be about 20.8vdc based on two 6800 ohms resistors in parallel (3400 ohms) feeding the mic load (if I'm thinking this through correctly).

    You are indeed thinking correctly Mark. It would seem the PS400 has a regulated supply but the supply to the regulator is not man enough. You don't say what the open circuit, no load voltage is Mark but my guess is around 47V (which is well inside spec) . The supply to the regulator hold up fine up to about 8mA.

    Caveat bloody Emptor!

    OP, if you want to use the Octava get a 10dB inline XLR attenuator as well as a supply AND CHECK IT! The attenuator will bring the level back to a "hot" dynamic. I am assuming you do not "kiss" the capacitor mic as you would a dynamic!

    Dave.

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    Phantom powering is tricky and has several problems:
    1. Phantom powering problem is reduced Phantom VOLTAGE. Without load it can be right +48V DC. But in case of Phantom's official max 10mA CURRENT's load std Phantom circuit provides under 15V DC VOLTAGE!
    Most case it is not so critical for impedance convertor buffer preamp. But some pro condenser mics are using Phantom voltage as POLARISATION voltage and provide distortion or even not work at all!
    2. Many (semi-pro and even some pro!) mixers/mixing consoles can not provide enough total Phantom CURRENT (not talking about voltage...) if several input channels (connected devices) are using higher current Phantom Power.
    Because inbuilt power supply is too weak for total Phantom load, as result 48V stabiliser can not even stabilise voltage and you have low current + low voltage + pulsing 50/60Hz hum...
    3. Phantom power can damage un-symmetric loads. The same can happen with less-transformer dynamic & ribbon mics in case of damaged (one signal wire shorted to shield/ground) mic cable.

  3. #13
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    Quote Originally Posted by Ainaudio View Post
    Phantom powering is tricky and has several problems:
    1. Phantom powering problem is reduced Phantom VOLTAGE. Without load it can be right +48V DC. But in case of Phantom's official max 10mA CURRENT's load std Phantom circuit provides under 15V DC VOLTAGE!
    Most case it is not so critical for impedance convertor buffer preamp. But some pro condenser mics are using Phantom voltage as POLARISATION voltage and provide distortion or even not work at all!
    2. Many (semi-pro and even some pro!) mixers/mixing consoles can not provide enough total Phantom CURRENT (not talking about voltage...) if several input channels (connected devices) are using higher current Phantom Power.
    Because inbuilt power supply is too weak for total Phantom load, as result 48V stabiliser can not even stabilise voltage and you have low current + low voltage + pulsing 50/60Hz hum...
    3. Phantom power can damage un-symmetric loads. The same can happen with less-transformer dynamic & ribbon mics in case of damaged (one signal wire shorted to shield/ground) mic cable.
    Whilst it is true that the maximum 10mA draw would only leave 14V on the mic pins any mic manfctr would surely know this? They would therefore be running the electronics as "current source mode" and deriving the polarization voltage from a DC-DC converter. Not forgetting as well that many, quite expensive and decent capacitor mics use electret capsules these days. Then of course, Sennheiser use a completely different principle and need no polarizing voltage.

    Yes, stories abound of ribbons being damaged by phantom power but actual, verifiable incidents are hard to find and of course, SOMETHING has to go wrong, open or short connection for badness to happen.

    I have been told several times that BBC OB trucks used P48 on every XLR and it was not switchable. They used a vast array of mic types including the venerable 4038 and I am sure "steps" would have been taken had even just a few been killed?

    Phantom power is perfectly safe when used correctly and by people who know their job. It is unfortunate now that gear delivering spook juice has fallen easily into the hands of people who do not. However, if those people take the time to learn a tiny bit of electronics theory AND get a frigging meter! Their kit will stay safe.

    Dave.

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    Quote Originally Posted by ecc83 View Post
    You are indeed thinking correctly Mark. It would seem the PS400 has a regulated supply but the supply to the regulator is not man enough. You don't say what the open circuit, no load voltage is Mark but my guess is around 47V (which is well inside spec) . The supply to the regulator hold up fine up to about 8mA.

    Caveat bloody Emptor!

    OP, if you want to use the Octava get a 10dB inline XLR attenuator as well as a supply AND CHECK IT! The attenuator will bring the level back to a "hot" dynamic. I am assuming you do not "kiss" the capacitor mic as you would a dynamic!

    Dave.
    You know, I did measure it, wrote it on a piece of paper, and then just forgot to note it in the post...... No load volts = 47.3vdc. Going to edit the post so it has all the measurements.
    Mark.......

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    Hi

    Ok thanks for the info guys. Is going a bit over my head now to be honest. My knowledge of electricity is I know that Amp x Voltage = Watts. That's about it.

    Mark: so are you saying that with this result:
    CAD M179, 8ma, 4.52vdc

    There's no way the PS400 will make an Octava Mk-219 work properly as the voltage is way too low?

    What I dont get is that if I plug the Octava directly into the UR22 there's no problem at all (there's only the hissing when it's running off the Mic Mechanic) No hissing, no noise and thats running off USB power so how come a dedicated unit like a Behringer PS400, that has more power going into it, couldnt power it?

    Thanks

    Masten

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    Quote Originally Posted by Masten View Post
    Hi

    Ok thanks for the info guys. Is going a bit over my head now to be honest. My knowledge of electricity is I know that Amp x Voltage = Watts. That's about it.

    Mark: so are you saying that with this result:
    CAD M179, 8ma, 4.52vdc

    There's no way the PS400 will make an Octava Mk-219 work properly as the voltage is way too low?

    What I dont get is that if I plug the Octava directly into the UR22 there's no problem at all (there's only the hissing when it's running off the Mic Mechanic) No hissing, no noise and thats running off USB power so how come a dedicated unit like a Behringer PS400, that has more power going into it, couldnt power it?

    Thanks

    Masten
    Yeah, I don't think the MK-219 would cut it with the PS400. If I get a chance I'll give the CAD M179 a try to see if it will function with the PS400. The spec sheet for the CAD states it will work in a range of 24 to 48vdc, but I have serious doubts it will do anything with just 4.5 volts.
    Your UR22 likely has a better power supply than the PS400, but if I were to guess, I'd bet if you had a second MK-219 to plug in and try to power, the UR22 may not like it and not provide enough voltage.
    Mark.......

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    how about a used Shure PS1A, power supply?

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    Quote Originally Posted by Toastedgoat View Post
    how about a used Shure PS1A, power supply?
    You woulda' thunk 48 vdc, but......
    48V phantom from PS1A?
    Mark.......

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    There's a review on the Thomann site that supports the above comments. not a wonderful unit with mics demanding the full current indicated in the spec.
    Just recently bought the PS400 for supplying phantom voltage to various condensor microphones. In brief: rugid built, however not meeting decent electrical specifications.
    - Output voltage (unloaded) equals 12V in 12V-mode, but only 31V in 48V-mode, i.e. much too low! A short check of the internal electronic circuits shows a multi-diode trippler, thus limiting the output to 3x the input voltage, i.e. 36V max. It never will/can reach 48V, as claimed!
    - The output voltage STRONGLY depends on microphone current drawing! E.g. in 12V-mode the voltage drops from its unloaded 12.0V to 10.4V (at 5 mA) and 8.5V (at 10mA).
    But much more serious in 48V-mode: from 31V (unl.) to 22V (at 0.7 mA) and 12.5V (at 2 mA)! Note that common microphones typ. require 2-5 mA at 48V!
    - Noise level is OK, both at 12V (adapter) as well as 9V (battery); at 9V unloaded output voltage is just 9V or 25V (select switch 12V- or 48V-mode).
    Fazit: at "48V" setting the unit can not be used. Likely many people will be affected by this deficit, without knowing.

  11. #20
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    "Ok thanks for the info guys. Is going a bit over my head now to be honest. My knowledge of electricity is I know that Amp x Voltage = Watts. That's about it."
    That's pretty much it Marsten. Ohm's Law. That is all you need to work out phantom power voltages although the process is a bit convoluted.

    Take our maximum spec of 10mA and 48V (the standard allows + or - 4V). The actual 48V supply in the AI/mixer/PSU should be capable of at least that current for each XLR outlet. From said supply are two 6,800 Ohm resistors, one in each "leg" pins 2&3. To K.I.S.Sir we can just combine them as a single 3,400 Ohm resistor (3k4) .

    Now, mA times k = V so 34V is dropped across the 3k4. Take that from our so-so solid (ha!) 48V and you get 14V at the pins of the mic.

    In theory, when any piece of gear go for a review the phantom power delivery should be checked for each mic input for voltage at max load current. Now, I can see that this is tedious for a 32 input mixer but they SHOULD do it. In practice they never do it even for a 2 mic input AI!

    I have been messin' with this stuff long enough to know that ten or so years ago AIs had pretty poor mic pres, at least at the budget end did say, sub 200? Every time one was reviewed the lack of gain and poor noise performance was, rightly, commented on. Result? You can now by a 2 mic input AI for less than 80 with very good pre amps that will work with a dynamic mic, at least for close talk/singing and cabs.
    "They" do listen if the right people make enough noise!

    Dave.

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