Preamps and Amplifiers for Vocal Recording?

R

Ryan Teasnob

Member
I never thought too much about this before. But now I'm curious :P. Audio recording interface units are always touting the quality of the preamplifiers. But when looking at the definition of "preamp," You usually see something like "microphones have low level signals that need to be boosted to line level via a preamplifier before being sent to an amplifier."

So in an interface like, say, a Focusrite Scarlett Solo, is there an "amplifier" that the mic signal gets sent to after it gets boosted by the preamp before going into the computer? If not, what does the "pre" in preamp really mean?

I'm having a philosophical day :P..
 
The term probably comes from mixing consoles where the signal has to be amplified ahead of the rest of the signal path so things like eq, summing buses and inserted processors work optimally.
 
Hi, Ryan!

As far as I know, you're right.

I think of a preamp as anything that boosts or shapes a signal before it gets to a power amp. In a guitar tube amp, the little tubes are for the preamp and the big tubes are for the power amp — both in one box.

And any overdrive pedal (or other powered pedal) is also a preamp. Likewise, you can put your own mic preamp between your mic and your Foucusrite. In a stereo system, you can get a separate preamp and power amp or, more commonly an "integrated" amp that, like a guitar amp, has both in one box.

So I assume that external interfaces (like your Focusrite) have preamps to bring in the signal and power amps that send those signals to your computer (rather than to a speaker).

But I've never thought about it. Someone else here will is sure to know.
 
Other than a headphone output (and even that's a stretch), there aren't power amps in USB recording interfaces. A power amplifier has to produce substantial current along with voltage gain in order to drive speakers. There's no need to do that in an interface.
 
After it goes through the interface, it will either go to a pair of monitors (active or passive with an amp) or headphones. Those would be the "amps"

Sometimes it amazes me how people overthink things. So, if you use an external preamp and plug it into an interface with a preamp, does the preamp become a pre-preamp, or does the preamp become an amp?
 
Focusrite et al are perfectly entitled to call the electronics front end of their interfaces "microphone pre amps" because a mic pre has a series of features that make it far from simple to design.
First of all of course it must have very low electronic noise allied to high gain, a feat that has only been achieved in modestly priced AI in the last five or so years. It is in fact almost impossible today to find an AI, even a very cheap one, that has an unsatisfactory mic stage.
We also expect the harmonic distortion to be at least as low as the A to D converter, i.e. in the third decimal place and that is not a trivial task with a balanced input amplifier.
The amp must also be able to have 48V phantom power slammed on and off of its input. You cannot do that to any old collection of transistors and op amps. You will pop 'em!

Paradoxically, although an AI's mic (and line for that matter) pre amps can usually raise a signal to a few volts the resultant signal must then be attenuated before it hits the A/D converters. Many here will know, digital chips work on 5V as a rule but in practice about 3.3V and the full drive from almost any standard op amp would blow the front end of the A/D C.

Dave.
 
bouldersoundguy said:
Other than a headphone output (and even that's a stretch), there aren't power amps in USB recording interfaces. A power amplifier has to produce substantial current along with voltage gain in order to drive speakers. There's no need to do that in an interface.
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Aha! So they're called preamps even though there's no amp.

That explains why my monitors were powered.

Good to know!
 
...... but of course, your speakers might not have a pre-amp and an amp, but others that have more facilities, might have. Even worse, how about an SM7B microphone user? They might have a Cloudlifter, which is also a pre-amp, then they'd have the pre-amp in the interface.

All joking aside - this is why proper gain staging is so essential. We get loads of questions with gain staging as the answer.

Cloudlifters are designed with low output microphones as the key. Their output is set to enable them to match properly to the next pre-amp, and then that needs to match the next device. It often goes wrong on guitarist's pedalboard where the order of the pedals in the chain is vital for ultimate performance. A noisy chorus unit, in the chain too early has it's higher noise added and added by every device. Knowing your gear is imperative. I saw a sound guy with a small 6 way analogue mixer, feeding multiple synths into one input of his very expensive digital mixer. The analogue mixer was working hard, flat out with red LEDs lit everywhere, yet the gain on the digital desk was way, way down to accommodate the very hot input? His answer, when I queried it was that the little mixer distorted really nicely when driven hard and the synths going through it were the 70's/80s buzzy sawtooth pad sounds and it made them sound better! Can't argue with what I heard.
 
Delmont said:
Aha! So they're called preamps even though there's no amp.

That explains why my monitors were powered.

Good to know!
Click to expand...
Stricktly speaking. all amplifiers are 'power' amplifiers, even ones with no voltage gain. Think of a guitar buffer amp, it just presents the guitar with a very high impedance, usually 1 meg Ohm but does not increase the signal voltage. However, any buffer worth its salt can drive a load as low as 1 k Ohm and so deliver a mA or two. Power in is infinitesimal, power out, though small is easily measured.

There ARE amplifiers that provide voltage gain but no current gain but they still put out more power than the driving source as a rule. Not an amplifier type you meet in audio work though. (Oh! Revox record amps...forgot!)

Dave.
 
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