● The reference voltage is developed across an exchangeable resistor which can also be an external adjustable resistor
● The control loop adjusts the bias such that current through the sampling resistor (10R) produces the same voltage as the reference voltage, but it does so extremely slowly, to reject the dynamic variations introduced by the music.
● During startup the Active Bias System is set to apply the maximum bias and is locked into this stage for around 15 Seconds. During this time the “Error” Leds are lit up (they may briefly flicker on/off as the control loops stabilises).
● The the Active Bias System starts ramping up the Bias voltage slowly, reaching full bias within around 45 Seconds.
● If any one Valve connected to the Active Bias System cannot be biased to achive nominal current, but continues to have increased current, the “Error” LED will re-light and the “Error” output will be pulled low (open collector) to allow external protection circuitry to protect the Amplifier from the defective tube.