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Thread: low phantom voltage for condenser mic????

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    solo2racr's Avatar
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    low phantom voltage for condenser mic????

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    I have been thinking about getting my first condenser mic (an AT-2020) but I am concerned about the fact that my mixer only puts out 30v for phantom power and not the 48v that the mic calls for. Questions is, what will happen if 30v and not 48v is used for phantom power?

    Thanks, Ken

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    dgatwood's Avatar
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    Quote Originally Posted by solo2racr View Post
    I have been thinking about getting my first condenser mic (an AT-2020) but I am concerned about the fact that my mixer only puts out 30v for phantom power and not the 48v that the mic calls for. Questions is, what will happen if 30v and not 48v is used for phantom power?
    Considering the AT2020 is an electret condenser, I'd expect it to work fine, but I certainly won't make any promises.

    True condensers (non-electret) would end up with lower capsule bias voltage, which would decrease sensitivity, IIRC, and if you ended up really starving it badly, you might end up with other problems. My ADK Hamburg, for example, seems to put out an obnoxious pumping white noise sound with preamps that don't provide enough voltage (or maybe not enough current---I haven't pulled out a multimeter to diagnose it since I don't own the mixer that I've seen this on) and becomes utterly unusable.

    Worst comes to worst, you can get an ART phantom power supply box and use that to provide a full 48VDC.
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    dementedchord is offline Psychotic State alumni ch
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    i suspect he's right about it being alright... trueth be told some can work on as little as 3v... but try it you're not gonna break anything in this case....


    dg.. ive seen that problem in a big A+H board once... voltage reg was bad.... his SM81's were sounding like shit....
    37.8% of all statistics are made up on the spot...

    hey give a guy some room... people are trying to evolve here... for crying out loud...

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    solo2racr's Avatar
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    That was a main concern. Didn't want to burn something up. The other was how it would effect the sound quality. I was thinking along the lines of more speakers get burned up from being under powered than from being over powered. But, not understanding the reason for the mic needing phantom power led me to ask the question.

    Thanks again, Ken

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    dgatwood's Avatar
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    Quote Originally Posted by dementedchord View Post
    i suspect he's right about it being alright... trueth be told some can work on as little as 3v... but try it you're not gonna break anything in this case....


    dg.. ive seen that problem in a big A+H board once... voltage reg was bad.... his SM81's were sounding like shit....
    This was in a Peavey powered mixer. I figure if the supply were completely bad, none of my other condensers would have worked. I subbed in an AT2020 and that worked. The board was also powering an MSH-4 (phantom-powered tube mic), a SP B3, and an MSH-2 at the time.

    I figured my Hamburg was just bad, but I brought it home and hooked it up to my Peavey PV8 (unpowered mixer) and it worked fine.

    Dunno.
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    mshilarious's Avatar
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    Quote Originally Posted by dgatwood View Post
    This was in a Peavey powered mixer. I figure if the supply were completely bad, none of my other condensers would have worked. I subbed in an AT2020 and that worked. The board was also powering an MSH-4 (phantom-powered tube mic), a SP B3, and an MSH-2 at the time.

    I figured my Hamburg was just bad, but I brought it home and hooked it up to my Peavey PV8 (unpowered mixer) and it worked fine.

    Dunno.
    The MSH-2 and especially MSH-4 are thirsty mics. Combined, they could bring an underpowered board to its knees, especially if the Hamburg also needs a fair amount of current or full voltage. Try testing an empty channel with the mics all attached, and see what the voltage is. A *compliant* supply should be no less than +44V.

    Most MSH-2s I made were intended to run on lower phantom supplies, the flip side of that was that the power supply circuit wasted current with full P48. Later on, I gave up on the low-voltage feature, changed the circuit, and listed it as +18V minimum. That was because some portable and USB pres were having trouble, which is sort of the opposite of what I had designed.

    The trick is a preamp manufacturer feels obligated to list a +48V voltage spec, even if that means very limited current from the pre's DC converter. It used to be that they would go with +24V and be happy, but that's not really a commercially acceptable solution anymore, even if most electret mics work fine with that. This thread is a good example: AT is conservative in their specs, so it wouldn't surprise me if the AT2020 did work with +30V. I think their SDC range (3031, 4041, etc.) are spec'ed at lower voltage though, so an email to AT support might be worthwhile. The Shure SM81 is spec'ed down to +9V, and I can confirm that the KSM141 works with +9V.

    Anyway, in your MSH-2, you might want to swap R1 and R2 to 10K. Or send it back to me and I'll do it without charge. That will save a few mA on your Peavey board.

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    dgatwood's Avatar
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    Quote Originally Posted by mshilarious View Post
    The MSH-2 and especially MSH-4 are thirsty mics. Combined, they could bring an underpowered board to its knees, especially if the Hamburg also needs a fair amount of current or full voltage. Try testing an empty channel with the mics all attached, and see what the voltage is. A *compliant* supply should be no less than +44V.
    It was a borrowed powered mixer that I used exactly once to do live sound reinforcement at a friend's wedding, so I can't really do any testing to figure out what was wrong.


    Quote Originally Posted by mshilarious View Post
    Most MSH-2s I made were intended to run on lower phantom supplies, the flip side of that was that the power supply circuit wasted current with full P48. Later on, I gave up on the low-voltage feature, changed the circuit, and listed it as +18V minimum. That was because some portable and USB pres were having trouble, which is sort of the opposite of what I had designed.
    I have no idea which one mine is, but probably the earlier design. I think I've had them for a year-ish.


    Quote Originally Posted by mshilarious View Post
    Anyway, in your MSH-2, you might want to swap R1 and R2 to 10K. Or send it back to me and I'll do it without charge. That will save a few mA on your Peavey board.
    Thanks for the tip. I might do that one of these days if I get around to it, but I have a few other modding projects ahead of that... like putting inline connectors on the capsule wires of a bunch of my LDCs and experimenting with some Peluso capsules.

    Again, though, your mics worked just fine (indeed, everything worked fine except the ADK), so I'm not gonna worry about it too much. In the rare situations where I do live sound, I always carry along my Peavey PV8 mixer just in case phantom is broken in some weird way on whatever board I have to deal with. Very portable, and plenty of phantom power.

    Just for grins, I just hooked up all three of my MSH-4s---two of the newer model with the large capsule and one of the older style with the MSH-1 capsule. My little PV8 handled it without breaking a sweat. For a hundred bucks, I know I'm impressed.
    Quote Originally Posted by Obi-Wan
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    solo2racr's Avatar
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    Yea, I was thinking that if you had a number of power hungry phantom powered mics plugged into a board that has 48V but not much current, the voltage would suffer and drop. It sounds like the consensus is that the AT-2020 would be fine. I tried to call them yesterday and all I got for well over an hour was a busy signal. I'll try to call again today and if that fails again, I guess an email is in order.

    Thanks everyone

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    solo2racr's Avatar
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    OK.......Trying to get any help from A-T is getting to be a joke. Their phone line was busy all day Fri so I shot them an email. The answer I got was that it did need 48v and then tried to sell me their phantom power supply. I sent an email back saying that I would probably get a new mixer with 48v before I would get their power supply. That was Friday late. The first email from them was answered rather quickly. I guess they saw an opportunity to sell a mic and a power supply. When I shot that down, it seems like they are no longer interested. Oh well.
    Last edited by solo2racr; 02-11-2008 at 20:54. Reason: typos

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    Finally got an answer from AT yesterday. The tech guy I talked to first wasn't sure about the AT-2020 working on 30v phantom and transfered me to engineering. The guy I spoke to there said that it HAD to have 48v for it to work. More would cook it and less wouldn't let it operate properly. He suggested a AT-3035 and that IT would work on the 30V phantom power that I have. At this point, I am more inclined to sell the mixer (it overkill for one person recording....12 channel) and get a Soundcraft Compact4 to plug into my soundcard. Trade quantity for quality. From there, I can get the AT-2020 as it puts out 48v phantom power. Now that my ducks are in a row, time to spend! QUACK QUACK

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