Bay Area DIYer’s should make it to the DIY Swap meet on Feb 21 at 924 Gilman St in Berkley CA.

For more info:

http://www.euthymia.org/

The first three were a great time lot’s people with lot’s of stuff. Anyone from the should meet up with me. I’ll try and wear my DIY Stompboxes t-shirt.

I had fun last week recording a Podcast with my pal Joe who put together some great series of sound clips highlighting various boosters.

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Download

Here’s a great thread. I’ll need to read it a few times before it all sinks in.

http://circuitworkshop.com/forum/index.php?topic=71.0

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.)

Assume there’s your favorite booster at the input, what is D2 doing? This is the most common clipping arrangement that I have seen. It seems that D2 does nothing.
If the boost at the input is running off 9V then the you should have a single that is centered on 4.5V going past the two diodes. D1 clips the signal when it is above 0.7V. D2 on the other hand should not allow a signal to pass until it gets above the reverse bias voltage.

Feel free to let me know what I missing if anyone has some insight into this.

Here’s a quick idea for a MosFet Range Booster.