This is one of the simplest OpAmp circuit which can be used as a clean volume booster or as an preamp into your speakers. With this simple circuit you can turn your any speaker system into a guitar practice amp. I first created it in separate box and then I directly installed in speaker itself using mini monojack socket so it can serve me as pedal too :)
This is a transparent, clean guitar booster for solo’s and other times when you need a couple of extra dB’s.
You can also use it to get some more gain out of an amp or distortion pedal. The circuit is a very common amplifier circuit built around a TL071-opamp. Other OpAmps can be used as well, but the TL071 is cheap and produces very little noise.
The ‘Boost’-knob controls the amount of boost, but can also attenuate the signal so you can use it as a sort of pre-settable volume knob.
• The maximum gain of this circuit is about 10 dB. If you need more (which I doubt), increase R2 (or decrease R1). The gain A = 20*log(1+(R2/R1))
• Rp is optional, it’s a pulldown-resistor to avoid ‘switch-popping’ when the effect is turned on. (I used it in my circuit)
• The circuit also acts as a buffer since it has a high input impedance (about 1 MOhm). This will give you more overall ‘clarity’ (high frequencies) when you’re using long cables.
• The booster is preferably used at the very end of the effect chain, just before the signal goes into the amp-input (or FX-return when using your amp’s effect loop).
(I got details from this link http://www.jer00n.nl/2010/07/28/clean-boost-for-guitar-or-bass/