what exactly is a preamp

[franklin01]

i am completely new to this whole guitar amp thing, and i have no idea how they work, for example, what is a preamp and what does it do? ive heard of thm but never really had thm explained to me, please help me!!
thanks

[Crystallas]

Its an amp that gives you a set of options and adjustments to add to the main amp.

[joecool85]

More specifically it is a device with an amplification stage, it boosts the signal high enough for the power amp to use it effectively.  A guitar normally only puts out a few tenths of a volt, a preamp boosts it to several volts.  Some preamps are just that one part I mentioned, others have EQ sections as well (treble, mids, bass) and even effects.

[franklin01]

ohhh, i think i get it now, so the preamp is the part usually near the top with all this nobs, and the power amp is the actual speaker? do i have this right??

[joecool85]

Close.  This is how it works:

Input (in our case, guitar) makes the signal, it gets processed by the preamp to make it into a usable voltage for the power amp.  The power amp amplifies the signal to speaker level, the speaker hooks directly to the power amp.

Input         [-----------PREAMP--------------] [POWERAMP]
Guitar ----> Treble | Mids | Bass | Volume | Master ----> Speaker

Does that help?

[franklin01]

ok so i get the preamp part, but please bear with me because now im having problems with the power amp part! so the power amp would be the part that has control over the speaker?(volume and such??)

[joecool85]

Sort of.  You can control the volume several ways.  The "master" controls how much volume is going into the power amp, the more that goes into the power amp, the louder it will be in the speaker.  You can also cut the preamp (which means less signal to the power amp) and that does basically the same thing.

[franklin01]

ok, so the power amp would be an actual cicuit board similar to the preamp right??

[joecool85]

Correct.

[franklin01]

ok so let me see if i have this right... in this schematic i found, , the power supply would be the bottom part, the preamp is the middle part and the power amp is the top part. do i have this right?? http://www.mif.pg.gda.pl/homepages/tom/files/cube60.gif

[teemuk]

Preamp is the top part excluding speaker/ headphone jacks at far right. Middle part is (from left to right): Jack for normal input, reverb driver, reverb tank output signal amplifying stage and everything right from "master volume" potentiometer is the power amplifier.

[d4v1d5hu13r]

Just to add to what he said, that's how Overdrive works. Well, in tube amps that is. If you have your preamp and master at say 5, and it's clean, and you pump that preamp to 10, it will 9.99/10 times clip. Thus you get anything from a light blues breakup to a heavy metal sound, depending on how many gain stages the preamp has.

Easiest way to explain tubes too it that they 'recreate the sound'. Like they take the sound and amplify it with rich harmonics that most SS amps can't get.

[Jack1962]

Basically most amps are built like this:

Input-------(PREAMP(Gain,Volume and Tone controls live here))-----Driver(this stage either split the phase for push_pull power amps or just boost he current for power amps)-----POWER AMP-----the Speaks



                                           Rock On

[katieburton12]

it takes a weak signal such as a microphone or guitar and brings it up to a line level signal. they can also include EQ and gain controls. then that signal goes into a poweramp that amplifies the signal for however loud it was designed for.
This should be in the guitar gear and accessories forum, unless you wanna build a preamp.

[Guitarist]

You have three basic types of amplifier. Where you draw the line is a little arbitrary but this is the idea. You have:
Pre amp
IPA Intermediate Power Amplifier
PA Power Amplifier
With audio, IPAs are not necessary. Neither is power transfer. With modern electronics, for audio we are concerned only with Voltage transfer. Hence, matching impedance is totally unnecessary unless you are making a telephone system with miles of wire.
So, given that we are talking guitar amps, the Pre amp purpose is to raise the voltage of the source (in this case a guitar pickup) to a leval useful to the Power Amp.  We have then raised the Voltage but have not yet given the ability to provide current at the voltage to develop useful power. It is easier and cheaper to add equalization and effects at low power so manufactures alway put equalization and effects in the preamp. It could be added in the power amp but would result in unecessary expense. Now that we have adequate voltage and all our equalizing and effects, we need power. So, we feed the output of the Pre Amp to a Power Amp. The Power Amp usually does not increase voltage but at unity voltage gain (ie no increase in voltage) adds the ability to supply current sufficient to drive a speaker (Typically 4 or 8 Ohm) If you try to drive a speaker with the output of a Pre Amp, the Pre Amp will be unable to supply the current to maintain the Voltage and hence the Voltage will drop and little or no sound will come from the speaker. The final Pre Amp stage may even overheat and destroy itself. This is why we have both Pre and Power Amps. Intermediate Power Amps are typically used in Radio where not only are we transfering voltage but indeed power.