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The Tesseract Boost/Preamp is an adaptation of the TC Electronic Integrated Preamp, a boost & EQ from the late 1970s. The Integrated Pre is so named because it’s designed to connect directly to your guitar, which is why the original unit did not have a bypass switch.
The Integrated Preamp gained fame as the secret behind Meshuggah’s guitar tone in the 1990s. The boost was perfect for pushing the front of their Mesa/Boogie Dual Rectifiers and the EQ can cut bass for a tighter driven tone.
The original unit could run on as much as 32V using an external supply, or it could operate at the standard 9V using a battery. Since 32V supplies are hard to come by, the Tesseract Boost/Preamp includes an on-board charge pump that quadruples the input voltage (minus a few diode drops), allowing a 32V operation from a standard 9V supply.
The only other modification is the removal of a pop-suppression circuit at the input. This is designed to prevent the loud pop when the input jack is first plugged in. It’s useful in the original unit that connected straight to the guitar since the preamp would reasonably be plugged & unplugged in a live setting. However, in pedal format, the suppression circuit has no function other than to increase the current consumption as it is always bleeding some of the supply voltage to ground. There is no impact to the tone or functionality if it’s omitted.
The Tesseract uses a charge pump to generate approximately +32V from a standard 9V supply. This is done by using a charge pump IC in a configuration that quadruples the input voltage. (In actuality, it’s a little less than quadruple due to the forward-voltage loss from the diodes.)
The Integrated Preamp user manual says it can be powered by “up to” 32V. The circuit can handle a fair amount higher than this, so it’s not a hard limit—it was likely just a standard power supply interval at the time. It could also be powered by a standard 9V battery, so there were a lot of options.
If you want the Tesseract to run on less than 32V, you can jumper some of the diodes and omit some capacitors to either omit the voltage multiplication entirely or else use it as a doubler or tripler instead:
Note that while the circuit will probably work with a standard TC1044SCPA, the LT1054 is recommended for its improved specifications and efficiency. It’s doing a lot more work in this application than a standard voltage doubler or inverter.
A word about the voltage: since the gain of the IC1 op-amp is fixed, higher voltage doesn’t mean more available volume. Instead, what it means is that it has more headroom. At 32V supply, the circuit can take a much higher input signal (2.5V peak-to-peak) and boost it to 25V p-p without clipping. Compare this to 9V operation, where it can only handle a 0.7V input signal and boost it to 7V.
Since passive electric guitar signals are only around 0.3Vp-p, this won’t make a huge practical difference. If you’re using it to boost an already boosted signal, though, this circuit can do a much better job than most others.
