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:
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.
- 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:
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Thanks! I am going to build a bass boost for my fender using this schematic!
i build this preamp with 14 db and have a brutal gain the best preamp
Erik, what changes dod you make to obtain 14dB?
Hi,
You can use the formula: 20*log(1+(R2/R1)).
If you keep R1 10k, and change R2 to 47k, the gain will be about 15 dB
Thank you! 15dB is what I was looking for!
“If you keep R1 10k, and change R2 to 47k, the gain will be about 15 dB”
Just re-read your post above:
Do you mean keep R1 100K (not 10K) and change R2 to 47K?
Sorry,
R1 should stay 100k
R2 should be changed to 470k
So there were two errors in my previous post
Then the gain will be 20*log(1+(470/100)) = 15,11 dB
This circuit is similar to the BBE Boosta Grande which also uses the TL071 opamp. But the Boosta Grande rolls off the highs as the volume is turned up. Does this circuit do the same thing? If so, can a component be substituted to stop the high freq rolloff?
This is the best booster and sound’s amazing but i have a serious “pop” when i turn “ON/OFF”!I already put 1M pulldown resistor from effect input to ground, but it’s same!Please help me
This preamp sounds GREAT!
Since I built this for bass I changed C1 to a 4.7uF metal film cap to let more bass through. I also changed UI to a LT1351 and the pot to a 25K log taper. More than enough gain for bass
i’ll go and make it now, thank you very much.
Hello,
Can you please send me the dimensions of the PCB so that I can have best fit
p.s. Sorry about the stupid question I’m just a hobby’st.
OK I got it…I made it and I have a small problem…Im having a serious buzz when the pot is from 0- 6 o’clock then the buzz is disappearing…Any help?
Change ur potentiometer… or variable resistor (1okohm on the picture)
where should i add diodes to make this into a distortion?
this thing sounds good, i built one and put a couple diodes at the end and get good distortion. how can i wire 2 of these in series to boost the sound from the distortion one in front of a clean one?
This is the best booster and sound’s amazing but i have a serious “pop” when i turn “ON/OFF”!I already put 1M pulldown resistor from effect input to ground, but it’s same!Please help me because it sound’s killer for me!
Thanks from Brazil!
Hello, greetings from Peru.. awesome booster .. just one advice.. if you want to mod it for 15dB output have to change only R2 to 470K on the schematics .. but on Layout you have to change R5 to 470K not R2 . Thanks Folks.
Jeroen thanks for sharing it, now is one of my favorite boosters, pretty clean, I’m running it at 12v for more headroom, works great.
I have just built one of these and used a NE5534 and changed R1 to 4K7 and R2 to 47K and it sounds great but what I would like to know, is there a way of cutting the highs by changing any of the components rather than having to add a tone control? Cheers.
you can add a cap between 10uF output and the 10K pot. wire the other end of the cap to ground. start at maybe 500pf and work your way up until you find the cap that gives you the rolloff you want