Guitar Amp Schematic

What is the point of a preamp? And how would building one differ to building a guitar amplifier?

WEll i just built my first guitar amp (Schematics below which i got from a website somewhere), and its awesome but i was wondering if i could improve on this design by adding a preamp before amplifier circuit? Im not sure what results i would achieve from this in terma of sound or loudness, but is it worth doing?
And also how would i go about it?

http://i54.tinypic.com/2crrspg.png

this is the link to the schematic

A preamp is used to increase gain, where the gain of the amplifier is not enough to allow the amp to generate it’s full rated power. Usually obvious that you need a preamp if the gain control is all the way up and you want to turn it further but can’t.

Preamp provides voltage gain, but it’s output can’t drive a speaker, only a power amp can do that.

Some preamps also have other special functions, besides gain. For example, a phonograph preamp would also perform the RIAA equalization.

In your circuit, the FET on the left functions as a preamp.

Don’t add a preamp unless it is needed.

The possible problems with your amp are insufficient power to drive your speaker(s), it can deliver less than 1 watt at the most.

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new 2 x 12au7 parrallel push pull combo amp running on 9 volt adaptor / smps