This is a transparent, clean guitar booster for solo’s and other times when you need a couple of extra dB’s. No ’boutique’ or other mojo-bullshit here, just a simple volume boost!
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.
Here’s the schematic:
- 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.
- 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).
Update: andre has provided a PCB layout for the booster: