Which simple boost for this use:

[alltrax74]

I want to add a simple - one knob / small board - boost in some of my dirt pedals, upfront the main circuit to act as a gain boost. It will always be on (no switch), so:
This boost must not change the tonal character of the pedal
When boost pot is fully CCW, it must be unity so that it's almost as if there were no boost, just the main circuit.

Any ideas, can a simple SHO or LBP1 do that ?

[fx-fidden]

I can say that the pot of the LPB-1 is a volume control, so at zero you have no sound.

The SHO could be better, because the pot is a gain control, and at zero it shouldn't give you any boost at all, I guess. At max it boosts a lot.
But I think the SHO is not super transparent, and the stock gain pot is "Crackle OK", it means that make some noise when you turn it.
Starting from the SHO you can set with a resistor a fixed gain setting instead to use a pot, and to add a master volume pot, using a resistor (maybe a trimpot) to the ground to set the minimum volume. (In case I'll try to help you).

Or, you can use a op-amp boost, that I found less noisy than transistor based schematic, and enough transparent.
I found casually a simple one:



I drawn (but still not tried it) a simple schematic of mine of a op-amp booster. If you want I can show it.

Or you can see the MXR MicroAmp. OpAmp based, clean enough, transparent enough. The gain pot works as you want, just the tape is not so linear.

[alltrax74]

Thanks for that exhaustive answer !
I see what you mean with the lpb1 : volume 1 to ground
I could maybe use the Soulsonic crackle not okay SHO, fixed resistor for the gain (to determine by ear ?), original output becomes volume 3, vol 2 to output and vol 1 to ground is that right ?

MXR Micro Amp or Shaka boost could be anoither solution, but if I'd prefer to keep the board smaller

[fx-fidden]

The "crakle not ok" SHO version can work.
Generically speaking I don't like too much that kind of gain control, I'm not sure how much transparent it could be, theorically, this kind of control.
But, I can't tell that it will not work for you.

If I have to suggest something, an opamp booster could work better, but it's my personal opinion and experience.
Let's see what other guys will tell you about it.

[Fuzz Prince Of Bel Air]

I see what you mean with the lpb1 : volume 1 to ground

Just stick a resistor between volume 1 and ground to get unity gain when the pot is at min.

My approach would be to breadboard a LPB-1, use a pot in place of that aforementioned resistor, adjust it until I get unity gain, guess (or use a multimeter to measure) how much resistance I've added, and replace the pot with a corresponding resistor.

However, you might find it useful to have less than unity gain. e.g. The Fuzz Face clean up trick of rolling down your guitar's volume.

[alltrax74]

Ys, I was thinking of trying that with the lpb1

[Sensei Tim]

I like the madbean bacon bits.

buffered, split rail, and volume at zero is unit gain.

http://tagboardeffects.blogspot.com/2014/10/madbean-bacon-bits.html

[alltrax74]

Yes, this is another possibility, plus i like the idea to have a buffer at the input of the dirt pedal. Thanks
One of my next builds will be the 5150 overdrive, and I'll try a few boosts upfront and will report back