Think of there being three separate types of components:
1) Preamplifiers
2) Power Amplifiers
3) Integrated Amplifiers
A preamplifier performs some or all of the following:
- switching of multiple inputs
- provides an external processor loop for connecting an equalizer or similar device
- volume control
- balance control
- tone controls
- tape recorder inputs and outputs
- phono preamplifier with moving magnet (MM), moving coil (MC) or both levels of phono stage preamplification and the required RIAA playback equalization needed to play vinyl records
- headphone output (if the preamplifier includes a built-in headphone amplifier)
Preamplifiers can provide signal gain but today, except for phono cartridges, most sources such as FM, Tape, CD, SACD, DVD-A do not require additional gain.
Preamplifiers can also provide buffering between the output impedance of the source unit and the amplifier. Mismatches in impedance between source and amplifier can cause audible frequency response variations, usually roll off of the high frequencies.
There are some preamplifiers that do not provide any gain, or rely on any powered (active) electronic circuits. These are known as passive preamplifiers. Passive preamplifiers are used to minimize adding noise and distortion to the signal ahead of the power amplifier, but without the ability to provide any gain.
Since little preamplification is going on, except as noted for the phono stage, a more descriptive name for the "preamplifier" is "control amplifier".
The power amplifier is responsible for accepting the signal from the source, either directly or by way of the preamplifier, and for powering speakers, headphones, or both. Most amplifiers intended for use with speakers are designed for an optimum output impedance of 4 or 8 ohms. Most headphones are of higher impedance that speakers, between 32 ohms and 300 ohms.
An amplifier designed to deliver 50 watts at 8 ohms will usually be able to manage to output just a few watts at 300 ohms. It is possible to overdrive headphones and burn out the drivers by connecting them directly to the output terminals intended for speakers, but this will happen with just a few watts of power being delivered to the headphones, not the rated power of the amplifier at the usual 4 or 8 ohms.
Most headphones need far less than 1 watt to achieve full output. To protect the user from overdriving their headphones using a power amplifier, sometimes an amplifier will include a headphone jack that is wired with resistors to drop the power level at the headphone output to a safe level, also one that is more easily matched to the output level when listening with speakers.
If the source you are intending to use has the means to let you control the output level, as with some CD players, and you only have the one source, you can connect this source directly to a power amplifier and use the output level control of the source device to control the volume. Also, some power amplifers include input level controls for each channel, functioning to limit the level of the input signal to the amplifier.
Many dedicated headphone amplifiers are better described as power amplifiers than as integrated amplifiers (see below) because the switching/control options of these headphone amplifiers are usually limited to one or at most two inputs and a volume control.
Lastly, integrated amplifiers combine the functions of the preamplifier (mostly commonly switching of inputs, volume, and balance) with the function of a power amplifier and have the ability to drive one or more pair of speakers and also provided outputs for headphones. Older integrated amplifiers usually include tone controls and a phono stage preamplifier, while current integrated amplifiers often leave out the phono stage preamplifier or make it available as an additional-cost option.
. What if I added a preamp to this system im building, as it's name suggest I would think that it goes before the amp, but I'm probably completely wrong =P
