Here's a bit of a trap for young players, or those who assume phantom = 48
volts. The old warhorse Shure FP42 four mics input field mixer (its been
around a long time !) actually has a published spec of 30 volts phantom
power, not 48...hell, it's not even T- power ! Heaven knows how they
arrived at that one ?? Might be ok with your cheaper condensor or electret
mics--which can live with lower phantom voltage....but expect a higher noise
floor and/or reduced headroom/ dynamics with more demanding mics !!
Just thought you should all know, for the sake of completeness.......lol !

Ray

In article writes:

Here's a bit of a trap for young players, or those who assume phantom = 48
volts. The old warhorse Shure FP42 four mics input field mixer (its been
around a long time !) actually has a published spec of 30 volts phantom
power, not 48...

The Shure Pro Master mixer provided 12V for phantom power, so they
make the SM81 mic (roughly contemporary) so that it would work on 12V.
The Mackie PPM series of powered mixers provide 15V for phantom power
(it's just tapped off the IC power supply positive rail).

Read the specs!

One spec that's rarely published is the total amount of current
available from the phantom supply. It doesn't seem like it should be a
big deal, and it isn't if there's a real power supply for the mics,
but often this is a place where manufacturers save money. Nowadays
with common and inexpensive condenser mics, it's not unusual for a
mixer to have nearly a "full house" of mic power, but half a dozen
years ago, some mixers derived phantom power using a voltage
multiplier, or a low current winding on the power transformer. They
were betting that only about 1/4 of the channels would need power, so
instead of having enough current for a reasonably greedy mic on every
channel, they limited the current available. Plug in too many
condenser mics and the voltage to all of them drops, sometimes to the
point where a mic no longer works properly.

--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

Mike Rivers wrote:

One spec that's rarely published is the total amount of current
available from the phantom supply. It doesn't seem like it should be
a big deal, and it isn't if there's a real power supply for the mics,
but often this is a place where manufacturers save money.

When the powering is inadequate, several different problems may
occur depending on the microphone's specific circuitry. Some of
these problems, such as lower maximum output voltage (which
corresponds to a lower maximum sound level), could ruin a live
recording without necessarily being obvious in a rehearsal or
a bench test.

That's why there are standards in audio. End users shouldn't have to
worry about details such as the exact resistance between the DC supply
and pins 2 and 3 of the XLR socket. But many manufacturers, especially
in the United States, seem neither to know nor care about standards.
This is a "chicken and egg" problem since the only way to hold them
to account would be if the customers were better informed--but again
the whole point of having the standards is so that customers can focus
on what sounds good instead of all these implementation details.

Some people feel that modern transformerless condenser microphones
don't sound as good to them as mikes made in the 1970s. But the
early 48 Volt phantom-powered FET microphones generally only drew
1/2 or 3/4 mA, while the ones made today draw 5 - 10 times as much
current or more, are often 5 - 10 dB more sensitive, and can handle
maybe 10 dB higher SPL. A mixer or preamp designed in the early
1970s may be compatible with a U 87 or a KM 84, but not with a
TLM 103 when someone is screaming into it, or when a percussionist
or pianist is playing a healthy, normal fortissimo.

The thing is, our ears can only tell us that something is wrong if we
know what it's supposed to sound like in the first place. When I see
people posting opinions of certain microphones, I sometimes wonder if
they've ever checked the phantom powering, the impedance and overload
point of the preamp or mixer input that they based their opinion on.
Those things are rarely specified in clear terms and they are never
mentioned in published equipment reviews--though that information is
absolutely essential for us to know what's compatible with what else.

--best regards

In article . com writes:

The thing is, our ears can only tell us that something is wrong if we
know what it's supposed to sound like in the first place. When I see
people posting opinions of certain microphones, I sometimes wonder if
they've ever checked the phantom powering, the impedance and overload
point of the preamp or mixer input that they based their opinion on.

The thing that gets me is when someone says "the preamp has very
little headroom." You can make as much headroom as you want by
switching in the pad on the mic if there is one, switching in the pad
on the preamp if there is one, (usually) turning down the preamp gain,
or putting a pad in line between the mic and the preamp.

What they usually mean is that with the gain set up fairly high so
they can tell how "sensitive" the mic is, when someone screams into
the mic, the preamp clips. One of the things that makes a mic preamp
design less than trivial is that it needs to be able to deal
comfortably with a wide dynamic range, but there's a maximum output
voltage for any circuit. If you put a sensitive mic in front of a
loud source and follow it with a lot of gain, you'll exceed the limit.

--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo