Discussion in 'Homework Help' started by mellowmon, Jul 28, 2009.
what should be the recommended bias current for this?
I take it that you are asking specifically about the Q5 setting. In an AB amp, that is often left to the taste of the individual. Technically, any setting that eliminates the zero crossing glitch is enough, but some people believe that a higher bias current (and operation closer to class A) produces superior audible results. More bias is more idling current, thus more need for heat sinking and fans.
That particular critter is strictly at your own risk. Results may depend on experience. You might want to look at Mike Leach's superamp as being a bit less daunting.
The article says the idle current is 165mA when cool which reduces to 40mA when hot.
in my own analysis it is imposible to measure 150mV across 2.2 ohm resistor because of the Vbe of otput transistor which is under 650mV and thus it is Turn on. the bias current should be measured across .47 ohm resistor.
Yes, the text in the project is wrong. The 2.2 ohm resistors need a lot more than only 150mV.
But you don't want 150mV across each 0.47 ohm emitter resistor because then the idle current will be too high.
across .47 ohm should only be 20mA or so.. per transistor.