How is output stage bias level set in the AKSA?
A small pcb-mounted, 25 turn trimpot is adjusted with a fine screwdriver. The adjusting screw is turned fully CCW at installation to set the trimpot to maximum resistance, the amplifier is powered up for the first time, and the offset voltage checked at the output. If it is below 30mV, the output stage is correctly activated, and two DMM probes are attached to the emitters of two complementary output devices. The trimpot is then turned CW until the voltage across two complementary emitters is 50mV, and checked after the amplifier has warmed over a period of 15 minutes, readjusting if necessary. The trimpot and associated bias network is trimmed so that the minimum idling current is around 3mA, and the maximum adjustment is around 150mA. This ensures that under any adjustment circumstances the bias level in the output stage can never be destructively high, allowing inexperienced constructors to breathe easy, knowing the output stage of the AKSA cannot self destruct during the vulnerable
Related Questions
- Would it be necessary for children to have used Numicon at the Foundation stage first, or could we start a group/class at the next level?
- Do the physical characteristics make a big difference in tactile transducer output level and frequency response?
- How do I get mp3 player output level to match phono input level (for use in a jukebox)?
