Update: This is the final version of the DR Booster:
The R10 is actually a pot, not a resistor. With R10 at 10k, the boost is 19.1 dB; At 0 it is 3.5 dB. The frequency band is 33 Hz – 2.9 kHz, with 330 Hz as the center.
Changing the output cap, C4, to 220n lowers the boost’s range to 18.7 db and 3.4, respectively.
At the minimum setting, the pot changes the band from 32 Hz – 3.2 kHz, with 320 Hz as the center frequency. As you can see, that isn’t as significant a change as the old design.
I did a lot of experimenting and this is the best I found. The bass isn’t too boomy, the treble isn’t too harsh, and the mids aren’t so much higher than the lows and highs that the bottom washes out completely or the treble is too subdued to easily get pinch harmonics. I really like this thing. I imagine it’s a lot like some clean boosts already out there, since the design is fairly basic, but I can say this pedal is specifically designed to enhance the character of a Dual Rectifier.
Additions to this circuit could include: a Volume pot in place of R6; a tone pot between R5 and C7.
The SPICE program is linked below in the original post.
The Original Text of This Post:
Here’s a slightly changed circuit for a boost to complement the Dual Rectifier. Compared to the first example, the band shifts from 82 Hz – 2.4kHz to 98 Hz – 2.3 kHz and the center frequency gets shifted from about 430 Hz to 475 Hz when the pot is at maximum. This is ignoring the optional treble cut. With the treble cut cap inserted (I’m using 4.7n), the center frequency shifts to about 500 Hz and the frequencies beyond 2.3 kHz are cut at a steeper rate.
All of these changes do two important things: 1) they reject noise from power and RF interference to a much greater degree, and, 2) it produces a boost more closely related to the overall bandpass of 95 Hz – 2.4 kHz (1.6 kHz for Vintage) for the Dual Rectifier. While the increase to the resistor in the feedback loop increases overall gain, the maximum Gain is reduced by .2 after the treble cut and isn’t a great loss. This version ranges from gains of 2 to 11 (nearly 3 dB to 20 dB), so a boost is always present at any setting when the pedal is on.
I used Tina from Texas Instruments to analyze the circuit. I’ll post graphs soon and I might make a few slight changes.
Update: I’ve been experimenting with some values to make it even more effective with a Recto. That will be posted here at some point.