Here’s a simple idea that you will work on almost every transistor
circuit out there. We’ll apply it to the MosFET boost here.

Remember the gain of the MosFET boost was determined by the Drain and
Source resistors. For the example circuit, as the Source resistor
decreases in value the gain increases.

A capacitor acts as a resistor when an AC signal is applied to it. The
resistance is dependent on the value of the cap and the frequency.
Lower frequencies see more resistance when the cap is smaller. This is
why you use a smaller cap to limit the amount of bass entering a
circuit. Or, use a larger cap to get more bass.

This idea can also be applied to the gain control to make a range
booster. Take a look at the attached file. Note that without C3 the
gain is 1 (assuming R3 and POT12  are equal). Add C3 to the wiper of
POT1 and you get a variable amount of gain to a frequency set by the
value of C3. Lower frequencies get attenuated.

When the wiper is at max resistance, you’re getting at least 5K before
the pot, so gain is 1. When the wiper is at minimum value the cap does
the variable resistance thing dependent on the frequency. Smaller cap
more highs get through. Higher frequencies see less resistance and
more gain, while lower frequencies see more resistance and less gain.

You can use this as an alternative to the SHO gain control by using a
large cap to boost a full range. Oops wait looks like Jack Orman did
it first. Take a look at his MosFET booster.

Here’s a typical MosFET boost. The gain is roughly determined by the ratio of Drain and Source resistors. Divide the Drain resistor (Rd) by the Source resistor (Rs) to find the gain. For example if Rd = 5k and Rs = 5k the gain is 1.
Use a Pot for Rs to set variable gain. Imagine POT1 as a 5k pot. Notice how the gain changes exponentially.

• 5k/5k = 1
• 5k/4k = 1.25
• 5k/3k = 1.67
• 5k/2k = 2.5
• 5k/1k = 5
• 5k/.5k = 10

Use a Reverse Log pot to get the linear feel for the gain control. (Thanks to Nelson on the forum for this tip.)

Here’s a layout for the MosFET boost. The drawing is pretty sloppy. But this shows the schematic and layout I used for my build. Seemed to work well. 

Here’s a link to a picture of my build. Here’s a link to the schematic on Muzique.com

This is Jack Orman‘s Minibooster.

This is design by John Hollis. It’s a booster that uses an inductor to generate a massive boost. It also has a switchable octave up. The boost sound is very warm and clear. The octave has a nice tone also.

There is a drop in volume between the octave and the boost, since the octave has to push the signal through a diode ring. This made it impractical to make the octave switchable with a foot switch. Hence the toggle.

I got the 3DPT toggle switches from FutureLec for a very reasonable price. I had to wait weeks for them. FutureLec is slow as mollasses, I would not recommend them if you are in a hurry.

This is Jack Orman’s Most FET Boost. This was an easy build. It sounds good, great clean boost with a lot of gain.

This is treble booster from the Stompboxology. This was an interesting new letter published by Nicolas Boscorelli. Who has, it seems, disappeared. If anyone has any information about this guy please email me! I looking for issues of Stompboxology. I have a few I can trade. There are some posted at http://moosapotamus.net/.

He also published The Stombox Cookbook. Which is very cool. It contains a lot of original and interesting Stompbox designs.

It has an interesting and original design based around a pair of FET’s.

Here’s the schematic that I redrew from the Stomboxology article.

Here’s a layout that I drew.