Phantom Power and Pre Amps

[rups712000]

Could anybody please offer me a simple defintion of Phantom Power and Pre Amp?

I am v new to this and am considering a mixer/controller/interface desk (new Roland si24). the desk itself has alanced Phantom power on the 8 XLR inputs, but I see no mention of Mic pres. Does this mean that I will also have to purchase a good mic pre unit such as a focusrite/joe meek?

Just for info I have an AKG C414 on order for the Mic itself....

with gracious thanks for your help here!

r7

 

[darrin_h2000]

The mixing desk preamps are there but the outboard ones will give you better results.

 

[sjjohnston]

A preamp (in this context -- i.e. a mic preamp) is device that takes the output from a microphone and amplifies it to a line-level signal.

Phantom power is +48 volts applied to the two signal lines in a balanced line, generally one that's connected to a microphone.

Mic preamps can be found in lots of devices: basically, just about anything that you plug a microphone into. Your standard mixer has mic preamps on some or all of the channels (however many have mic inputs). There are also numerous boxes that are just mic preamps (or a mic preamp combined with something like a compressor), which are often referred to as outboard mic preamps. An outboard preamp may be better or worse than the preamp in a mixer, depending on: (i) what outboard you're talking about, (ii) what mixer you're talking about, (iii) what you're trying to accomplish.

Condenser mics (other than some electret condensors) require phantom power in order to operate. Just about all outboard mic preamps supply phantom power. The preamps built into other things sometimes do, and sometimes don't ... I guess depending on how the designer expected they would be used. There are also boxes available which just supply phantom power.

 

[ozraves]

here is tim farrant's explanation he posted on hc:

***

Phantom power is a "loose" type power supply. Without getting too technical, the power is generally applied to the mic line via resistors. This means that with no load (ie no microphone drawing power from the line) it will measure around 48V or so. When you hook on a mic that consumes power (condensor) then the actual voltage on the mic line will drop, depending on the amount of current (or power) the mic requires.

For example, with 6k8 ohm feed resistors in the preamp (typical) and a mic that consumes 5mA of current (typical) then you will actually measure about 20V on the mic line. This is still enough because a typical solid state studio condensor mic has an internal working voltage of only 12V (depending on the design of course).

The voltage loss encountered is why such a high voltage (48V) is used in the first place. The feed resistors are necessary because you don't want the AC signal (audio) on the line shorted out by the DC (48V) supply.

Hope this helps to understand what "phantom" really is and why it is called that.

Cheers
Tim.

***

tim is the genius designer at buzz audio.

steve
www.piemusic.com

 

[Richard Monroe]

Rups, a search on preamp threads here will give you more data than you can stand. This is the reader's digest version- Your board has preamps, but not all preamps were created equal. They vary in price from about $5 (each pre in a cheap Behrenger mixer) to $4000 per channel or more in some cases.
Most of us can't afford 10 or 12 great channels, so we tend to set up 2-4 channels (or even one) that simply has a better grade of signal chain. Top notch cables, good pres, and good compression/EQ. For something requiring more inputs, (drums, etc.), you use whatever preamps you have. Condenser mics (except tube mics, which have a separate power source) have to have phantom power, usually +48v of it. Dynamic mics don't care about it, and ribbon mics are incompatible with it. In the end, the answer to your question is- you only need a preamp if you want better sound than the preamps in your board can make. You have to decide, but most home recorders will agree you need a preamp now or later, probably more than one.-Richie