BeePre2 Output Upgrade - Hybrid Shunt Regulator and Low Impedance Balanced Output

With the optimizations in the BeePre 2 circuit to increase signal to noise ratio and decrease build complications, we used a fairly conventional CRCRC high voltage power supply and no regulation. We also stuck with a single active tube stage for simplicity and a minimalistic approach.

Our second upgrade for the BeePre 2 adds an additional C4S active load per channel feeding our hybrid shunt regulator circuit used in all of our high end products. The stouter half of a 6CM7 dual triode handles shunt regulator duties in each channel, and these changes provide a sense of greater bandwidth and dynamics. The second half of each 6CM7 serves as a buffer for the output of the preamp, which gives the BeePre 2 a substantially lower output impedance (about 400 ohms from the unbalanced output) and allows for the addition of balanced XLR outputs. As a bonus, the turn-on thump associated with these simple single stage circuits is removed due to the slow warm up behavior of the cathode follower and the lack of direct coupling.