What's the difference between audio and pre amplifier ?

Hi all,

I'm rather ignorant about audio circuits, I was just wondering
is there some sort of convention regarding what would be
called an "audio pre amplifier" as opposed to simply
"audio amplifier"

 

An audio preamplifier takes the low level audio signal from microphone, turntable etc and amplifies it, to make it of a suitable amplitude for the input of an audio power amplifier. It often incorporates volume and tone controls.
The audio power amplifier converts this input voltage to a power signal of sufficient watts to drive loudspeakers.

 

Hi,

'pre' simply means before, so a 'pre-amplifier' is an amplifier
in front of another amplifier. It is usually of higher sensitivity
and lower noise than the main amplifier and often combines inputs
from several sources, levels and impedances together with such
additions as RIAA equalisation.


Cheers - Joe

 

Is there some convention regarding power of voltages, for example
up to so and so voltage it is a signal which requires a pre-amplifier
and beyond so and so voltage we use an audio amplifier proper ?

 

kind of. You are usually looking at an input signal of 100mV (or less) to
about 2V (for a CD player) going into an audio preamp. This could be
considerably less for a microphone.

 

A preamp accepts millivolts and puts out a volt or so,
whereas a power amp accepts a volt and puts out tens
of volts. But a more important difference is that the
power amp can drive a lot of current through a low
impedance load like a speaker (4 or 8 ohms), whereas
a preamp is only supposed to drive a high impedance
like the input to the power amp, typically 10000 ohms
or so. There are no numerical rules; the distinction
is usually pretty obvious in practice because there aren't
a lot of applications for things in between these extremes.
An exception might be driving headphones; they are
relatively low impedance (say, 8 ohms to 600 ohms or so)
but they don't take much voltage to get high levels. So
a preamp may inlcude a headphone driving stage (separate
from the stage that drives the big power amp), and this
headphone stage is really just a little power amp.

So to make a long story short, the main distinction is
probably the impedance they drive. (But somebody
is sure to bring up tube amps driving high-Z electrostatic
speakers or something...)





Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

Hi Bob,

Are those pre-amp useless, if your audio is already pre-amplified?

I would like to hook up my stereo amplifier to the PC audio output. I
think audio form PC is already pre-amplified and thus may not need any
further preamplifier outside.

By chance this stereo amp is already having a pre-amp, which is
followed by a power amp.

My problem is where to connect the input, to the pre-amp or directly
to the power amp?

Will the pre-amp burn out in the first case?

Thanks in advance

Best regards,
Animesh Maurya

 

Animesh:

Most preamps have an input for things that
don't really need any further amplification.
Aux, CD, Line In and probably most Tape In
fall into this category. The only input to avoid
is Phono, which is definitely for low-level
signals, or Mic, which few peamps have anyway.
Even then, the most you probably have to
worry about is grossly distorted sound; I
doubt you will blow anything.

The advantage of going through the preamp
section is the volume, tone, and balance
controls, plus the simple switching when you
want to listen to another source.

Hope this helps!


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com