A stepped-level control for Bruno Putzeys' Balanced Preamp project (Vol 5)

In Linear Audio Vol 5, Bruno Putzeys published an excellent article, called “The G Word”, explaining the importance of carefully treating the signal and its reference as a complementary pair of signals and how to prevent uncontrolled connections to (dirty) ground reference. Vol 5 came wih a free PCB to turn all theory into a practical project.

The level control with a linear potentiometer cleverly circumvents the non-linear properties of such a device. The implementation meant that at one extreme of the rotation, the gain of the preamp rises to infinity. Although in normal use that would not be an issue, inadvertent full rotation cannot be ruled out. Placing resistors in series could have fixed that, but that would negate the cancellation of the pot’s non linearity.   

To make a very good preamp even better, Hans Polak decided to design a replacement circuit for the pot that retains all the advantages and solves the remaining issues mentioned above. Here is his short article, including a small PCB design that fits right in. Thanks to Hans for a worthwhile addition!