If You Already Have Phantom Power, Do You Need a Mic Pre-Amp?

[HD_Dude]

I have two recording techniques.

One is an M-Box...with Pro Tools.

The other is a Marantz PMD661, portable digital recorder.

Both of those provide 48V phantom power.

If I record using a Neumann KMS 105, or TLM 103, or any other condenser mic, will I benefit from a mic pre-amp?

I know that sometimes you need a pre-amp to provide the phantom power if your recording gear doesn't have phantom power...but if it does, would a pre-amp make the sound better?

I'm guessing that a good pre-amp delivers much more than just power. But I'd love to hear your thoughts.

Thanks!

 

[SouthSIDE Glen]

I have two recording techniques.

One is an M-Box...with Pro Tools.

The other is a Marantz PMD661, portable digital recorder.

Both of those provide 48V phantom power.

If I record using a Neumann KMS 105, or TLM 103, or any other condenser mic, will I benefit from a mic pre-amp?

I know that sometimes you need a pre-amp to provide the phantom power if your recording gear doesn't have phantom power...but if it does, would a pre-amp make the sound better?

I'm guessing that a good pre-amp delivers much more than just power. But I'd love to hear your thoughts.

Thanks!

Both of the devices you mention already have the mic preamps built into them. So the answer would be yes, one does need mic preamps, but you already have them, so you don't need to go out and buy separate ones (though far more expensive separate ones can sound better.)

G.

 

[RawDepth]

Most microphones deliver a very weak signal. (Except for maybe tube mics.) The primary job of the preamp is to boost the signal level to a usable and healthy level for the rest of the system. Most often, you will find that you do need a preamp for at least a little signal gain. You should always start with the preamp gain setting at its lowest level and only raise it as needed to achieve an adequate level at your recorder. Other things like effects, EQs, and compressors should not be used to boost signal gain because they don't do it cleanly enough. If used, those should be placed in line after the preamp so they will receive a strong enough signal. Some preamps have those bells and whistles built in but the signal boosting part is still the most important part of its job.

Condenser mics usually need a low voltage to function thus the mic preamp is the most logical place to put the phantom power. If you have a separate phantom power box it should always immediately follow the mic in the signal chain because that voltage should not be routed to or through other audio gear. It may cause damage if the other gear is not designed to pass it through. I believe most decent mic preamps provide phantom already built in and ready to send to any mics that may need it.

So you see, the preamp is not there solely to provide phantom power to the mic. That is more of a secondary luxury.

 

[Mike_J]

Or the flip side to that....
While I use a channel on my Soundcraft mixer to boost the signal from my SM57, I find that I have to use a channel to reduce the input from a condensor mic as it picks up so much sound. (This is micing a guitar cab.) Does anyone else find this or have I got it wrong somewhere?

 

[SouthSIDE Glen]

Or the flip side to that....
While I use a channel on my Soundcraft mixer to boost the signal from my SM57, I find that I have to use a channel to reduce the input from a condensor mic as it picks up so much sound. (This is micing a guitar cab.) Does anyone else find this or have I got it wrong somewhere?

Don't mistake the function of the mixer with the function of the mic preamp within the mixer.

Every microphone needs to run through a preamp. Here's the point; all audio gear is designed to work at standard voltage levels so that they can send the signal to each other at standard levels. This level is called "line level". The problem is that microphones are necessarily very low-voltage devices; shaking the mic diaphragm back and forth with sound just does not generate huge amounts of electricity. So the signal from the microphone has to be amplified to get the signal up to line level voltages so it can work correctly within the rest of the gear. Since it has to be amplified before it can be further used, the device that does that amplification is called a pre-amplifier ("amplify before").

This is true regardless of microphone design. Some mics may output a bit more voltage than others (a.k.a. "hotter mics"), but even the hottest mic is still outputting far less than line voltage and will still need preamplification. You just won't need to have to turn the preamp gain up as far for the hotter mic.

G.

 

[HD_Dude]

This is really helpful...thanks to everyone who's contributing.

Yet another question...why is it so many microphone pre-amps have an XLR input, but a 1/4" output?

Is it because, as Southside Glen said, the pre-amp changes the mic level to line level? And in most cases the next element in the 'work flow' has 1/4" inputs?

Is there any drawback to having the 1/4" outputs? Or should I look for one that has XLR outs?

BTW I'm looking at the dbx 286A. Thoughts?

Thanks again!

 

[Seafroggys]

Most audio interfaces use 1/4" inputs and outputs as a standard for line-level stuff. Thus, preamps output to 1/4" so they can plug right into audio interfaces.

EDIT: Of course, you can get XLR->1/4" cables as well

 

[Mike_J]

Don't mistake the function of the mixer with the function of the mic preamp within the mixer.

Southside Glen-I assumed that my Soundcraft mixer had a built in preamp as it brings mic levels up well. In fact, I thought that most mixers had built in preamps. Am I sucking eggs here too? Should my chain be: mic-preamp-mixer-audio interface-PC?

HD Dude: XLR inputs are correct for mics I think.

 

[oretez]

while there are 'line level' mixers that would require outboard microphone pre-amplifiers (to bring the current generated by the microphone capsule flopping around in response to audio pressure wave up to 'line level')

the majority of general entry level offerings from Mackie, Allen & Heath, Soundcraft will have some form of microphone pre-amplification built in

as a gerneral rule of thumb if the mixer has XLR inputs it probably has some form of mic-preamplification

that said the expanding universe of mic design the variety of chaos of goals home recordists are attempting to achieve means that at some point expanding the pallet of microphone pre-amplifiers usually seems like a good idea.

But there has been a lot of quite respectable music produced via a mic into an entry level Mackie into an entry level sound card

 

[SouthSIDE Glen]

Southside Glen-I assumed that my Soundcraft mixer had a built in preamp as it brings mic levels up well. In fact, I thought that most mixers had built in preamps.

You're not sucking anything, Mike; you are correct .

Maybe I misunderstood what you meant in the earlier post, but when you said that you needed to "use a channel to reduce the input from a condenser mic", within the thread context of when and why mic preamps are used, I was just pointing out that one will always need the preamp built into the mixer to *boost* the mic voltage up to line level, no matter how you slice it.

The "input/trim" knob at the top of the mixer channel is the gain control for the preamp. Now maybe in relation to using another microphone you may need to turn down the amount of gain for the condenser vs. the other mic, but there is still preamplification going on. In other words, you're still boosting the level of the input signal, just not by as much.

Yet another question...why is it so many microphone pre-amps have an XLR input, but a 1/4" output?

For far more mundane reasons than one may think . It's really more just a convention than anything, but in general, XLR connectors tend to be more rugged than 1/4" connectors, yet at the same time they are more expensive and take up much more room on the back panel of your gear.

This combination of features means that XLRs are well-suited for microphone connections because of their ruggedness being used in stage and live studio situations where they can be exposed to the elements or drunken musicians or both. But their cost and size can make them less-suited for intra-gear connections within a studio control room; take a look at the I/O panel for your typical mixer or patch bay and just imagine how much room it'd take up and how much it'd cost to replace those dozens and even hundreds of 1/4" connectors with XLRs. And since (except for patch bay patches) the majority of those cables will remain left alone and relatively untouchable in your typical studio control room situation, the ruggedness factor is not as important.

Otherwise, the type of connector does not necessarily signify anything, they are just connectors. There are many pieces of pro gear out there - usually the higher-end stuff - that never see a microphone that provide XLR connections for their standard line-level inter-connections, and there are *some* - not many, but some - microphones that are hard-wired with 1/4" cable connections and a few more than that of mixers or interfaces with 1/4" inputs that do accept microphones and have mic preamps behind them.

G.

 

[Mike_J]

SG and oretez: Thanks for clearing that up for me. Appreciated.

HD Dude: Apologies for hijacking your thread. Sorry mate.

 

[HD_Dude]

HD Dude: Apologies for hijacking your thread. Sorry mate.

No such thing as hijacking as long as we're all learning.

And I am.

Thanks, everyone.

 

[HD_Dude]

You're not sucking anything, Mike; you are correct .

Maybe I misunderstood what you meant in the earlier post, but when you said that you needed to "use a channel to reduce the input from a condenser mic", within the thread context of when and why mic preamps are used, I was just pointing out that one will always need the preamp built into the mixer to *boost* the mic voltage up to line level, no matter how you slice it.

The "input/trim" knob at the top of the mixer channel is the gain control for the preamp. Now maybe in relation to using another microphone you may need to turn down the amount of gain for the condenser vs. the other mic, but there is still preamplification going on. In other words, you're still boosting the level of the input signal, just not by as much.For far more mundane reasons than one may think . It's really more just a convention than anything, but in general, XLR connectors tend to be more rugged than 1/4" connectors, yet at the same time they are more expensive and take up much more room on the back panel of your gear.

This combination of features means that XLRs are well-suited for microphone connections because of their ruggedness being used in stage and live studio situations where they can be exposed to the elements or drunken musicians or both. But their cost and size can make them less-suited for intra-gear connections within a studio control room; take a look at the I/O panel for your typical mixer or patch bay and just imagine how much room it'd take up and how much it'd cost to replace those dozens and even hundreds of 1/4" connectors with XLRs. And since (except for patch bay patches) the majority of those cables will remain left alone and relatively untouchable in your typical studio control room situation, the ruggedness factor is not as important.

Otherwise, the type of connector does not necessarily signify anything, they are just connectors. There are many pieces of pro gear out there - usually the higher-end stuff - that never see a microphone that provide XLR connections for their standard line-level inter-connections, and there are *some* - not many, but some - microphones that are hard-wired with 1/4" cable connections and a few more than that of mixers or interfaces with 1/4" inputs that do accept microphones and have mic preamps behind them.

G.

I really appreciate you sharing your knowledge here. I think there's a way of thinking that says XLR is pro, but I'm discovering there's a robust use of both XLR and 1/4".

My issue was...what's downstream? Does the next element use XLR or 1/4"? I usually try to avoid adapters, if possible.

My Marantz PMD661 has XLR inputs, switchable from mic to mic w/48v Phantom power to line, but also lots of other alternatives...from RCA analog to Coax digital to 1/8" analog...

Of course, my older M-Box has XLR and 1/4"....so that's NP.

Thanks to this forum I'll be able to work out a logical flow, from my new Neumann KMS 105 to the dbx 286A to either the Marantz or the M-Box.

Thanks, all.

 

[Richard Monroe]

Yo HD! Don't confuse the signal with the type of connectors. Mic level signals can be carried by 1/4" or XLR connectors. So can line level signals. There are also older, less commonly used types of connectors that mics can use, including tuchel and amphenol conectors. In general, audio signals can be carried by balanced or unbalanced connections. Balanced connections use 3 conductors, and 2 of them share a common ground. This is the type that uses a TRS 1/4" connector (tip-ring-sleeve). This is commonly misidentified as a stereo connector. An unbalanced connector is usually the TS (tip-sleeve) type, similar to a speaker or instrument 1/4" cable. XLR connectors are usually used for making balanced connections, but not always.

My Avalon preamp, for instance, has *unbalanced* XLR outs, as well as balanced ones, which I use to connect to an RNC compressor, which does not support balanced connections. So what is the next connection in the signal chain? The answer is- whatever connections the units you are using are designed for. Unbalanced connections result in a slight loss of gain, about 6db, (which isn't that much in the greater scheme of things), and result in increasing noise as the length of the cable run increases.

So people will tell you to always use balanced connections if you can, and that's true, but if your cable lengths are under 20 feet, it doesn't really matter. Unbalanced connections were used in studios all over the world for many years, and civilization as we know it did not come to an end. If you've got a 100 foot snake, it matters. As far as balanced connections go, there is no difference between 1/4" and XLR connections, except that 1/4" cables are easier to pull out accidentally. They also take up less room, and are easier to pull out *on purpose*, which is why most patch bays use 1/4" connectors.

Be aware, however, that even if a mic puts out a very weak signal, it is looking for a certain amount of resistance from whatever it is plugged into. Most modern mics with XLR connectors are low impedence mics, looking for a low impedence mic input. Many older mics are high impedence mics, called high-z, and are looking for an input more similar to an instrument input. These antiques may actually need to be plugged into an instrument input, like a guitar amp. Some very old PA's and preamps only had high-z inputs. It is a clue if the mic comes with an unbalanced (T-S) 1/4" plug at one end, and the other end is threaded, and screws on to the mic. Plugging one of these into a modern low impedence mic input is bad voodoo, and the results may be pretty ugly.

Southside Glen has stated that mics have low output, and need a preamp to raise the signal to line level. Be advised that 99.9% of the time, this is true. The rare exception to this is a line level microphone, such as Shure SM82, which has the preamp built into it. I plugged one of these babies into my Avalon after buying it at a yardsale and fried half of a $3000 preamp! Fortunately for me, Avalon fixed it, but the moral of the story is- lots of things can come out of an XLR connector, and it would be a good idea to know what that is before you plug it in. If I had looked that thing up on line, I wouldn't have fried a preamp, and blown the cones out of a perfectly good set of headphones while I was wearing them!

The other moral of the story is that to almost every rule in audio, there is some weird exception.-Richie

 

[RawDepth]

...(snip)...BTW I'm looking at the dbx 286A. Thoughts?

Thanks again!

dbx gear has been getting very popular within the sound reinforcement industry. Probably because it is somewhat road-worthy and moderately priced. Although those engineers usually don't have much need for separate mic preamps.

Having all those processed dynamic effects built in can be nice once in a blue moon if needed, however, they can add a lot of self noise (hiss) very quickly if you are not careful. If that noise is full spectrum then it is in your track for good, you will never filter it out. Also if you compress or expand too much while recording then you are stuck with it unless you have the luxury to re-track. In a live recording situation that wouldn't be possible.

I prefer to track cleanly (mic>preamp>recorder) and then process the tracks for dynamics later if needed. That way I can *undo* and *retry* as many times as needed to get it right.

 

[JIMBOdrummer]

also remember that dynamic mics do not require phantom power

 

[mixsit]

..Maybe I misunderstood what you meant in the earlier post, but when you said that you needed to "use a channel to reduce the input from a condenser mic", within the thread context of when and why mic preamps are used, I was just pointing out that one will always need the preamp built into the mixer to *boost* the mic voltage up to line level, no matter how you slice it.

The "input/trim" knob at the top of the mixer channel is the gain control for the preamp. Now maybe in relation to using another microphone you may need to turn down the amount of gain for the condenser vs. the other mic, but there is still preamplification going on. In other words, you're still boosting the level of the input signal, just not by as much..

.. Be aware, however, that even if a mic puts out a very weak signal, it is looking for a certain amount of resistance from whatever it is plugged into. Most modern mics with XLR connectors are low impedance mics, looking for a low impedance mic input.

Not to put to fine a point on this, but in some cases the output on a hot condenser on a loud source can be at or near line levels. It's not unusual to have to use (or need and have to pad down to) no gain at all. And you'll notice that while their mic outputs are fairly low impedance (600 ohms or so?) they like to see and operate better into higher input impedances, >1K, typically 5 or 10k ohms.
Basically a condition where a mic can be operating very similarly to a line level device.