For those readers who are not Brian May enthusiasts, I’d like to draw your attention to this innovation by Nigel Knight of Knight Audio Technologies (KAT): the BM RS Superpot. It is a dual-ganged stereo 250 kΩ potentiometer fitted with a 1 MΩ resistor and a 2.2 nF capacitor. It was designed by Nigel to serve a specific purpose: that is to linearise the response of a standard audio (logarithmic) taper volume potentiometer to increase the range over which Brian can control the transition from ‘sparkly cleans’ to sweet overdrive while performing on stage. Nigel flew out to Portugal to fit it to the Red Special before the Lisbon Queen + Adam Lambert concert on 7th June 2018.
Nigel explains: “When you cascade potentiometers you end up with a super-log pot, so the effective end result is a ‘forced’ log taper. Secondly, because after about halfway round the volume sweep of the RS, the pot is no longer really being used as a volume control, but more of a distortion drive which requires a more linear taper. So the new pot is more log at the bottom and more linear at the top. This allows better control over the cleans and smoother transition through the various stages of distortion. In fact, there is no discernible point where the distortion comes in with this configuration. It just slowly feeds in from the cleans.”
“The function of the capacitor is to compensate for high frequency losses while the resistor is there to pull the bottom leg of the pot to ground. The pot (short for potential divider) can’t ‘divide’ the level if it has no reference to the two points it is dividing between. The new pot gives Brian an array of tones that used to reside within about half a degree of pot movement (if you could find the sweet spot in the dark)”
Nigel has published a diagram of the pot shown in the image above. You can download it here: