Instructables
Picture of Clean boost for electric guitar
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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.

Notes:

• 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/)
samtechpro11 months ago
Hi dude..!! this circuit works with LM386 too so please mention the name in the alternative OP-Amp because TL071 is sometime hard to find for others. Have a wonderful day