Candy Buss CB2 Complete 2-Mix Signal Path Upgrade

As studio techs who maintain vintage large format analog mixing consoles, we are occasionally asked to install upgrades (aka “mods” or “retrofits”) in certain consoles. Once such popular upgrade is to replace the IC op amp-based mixbuss in any virtual earth console (which includes most consoles from mid 70s through present) with a set of discrete transistor amps for perceived sonic improvement. After doing this several times as a custom one-off, John Klett decided it was time to make the end-all PCB solution and that NonLinearAudio would manufacture and sell it as a kit product to be installed by us or other qualified techs, so he specified systems requirements and hired Jens to draw something beautiful. CandyBuss CB2 is the result, pictured below. You can buy one at

In addition to discrete current summing, CB2 includes several other useful features and a heavy-duty build throughout. Design goals met include:
– 100% common through hole components for easy field repairs in the future
– transformer balanced throughout, and capable of driving very demanding loads
– generic 2520/990 footprints for main summing and output amps
– an insert loop with controls for bypass and A/B audition
– return circuitry is full removed when insert is bypassed
– easy to reverse polarity throughout, to maintain phase coherency in any console system
– separate monitor amp outputs to feed control room section
– additional buss drop-ons for aux sources and cascading mixers (e.g. sidecar sum).
– discrete logic and JFET switching (used very carefully for lowest distortion) – no fancy ICs, nothing obscure
– incredibly desirable sound quality (which is a given)