@IanHegglun
Hans Polak shared ML33 adaptive bias in
The Black Hole... #8472. Seems operable without thermal compensation and simpler than #167.
Here's what I found in the ML33.
There is a significant change in bias current when the temperature of the power transistors heat up. Going from 27C to 77C the idle current changes from 100mA (my choice) to 232mA, see plot below, and still needs thermal feedback to stabilize the idle current.
(I chose 100mA by changing P1 to 33k - I wanted to see if there was an optimum bias, where the crossover gain wobble dipped down, white plot, but it doesn't, instead the bias loop breaks up (at high swing) if the idle current goes under 90mA).
There is an increase in bias current when the temperature of the power transistors heat up because the power transistor b-e junction is outside the bias loop Q3,Q4,M1,M2,D1,D2. The ML33 is similar to the Tanaka AES 3/81 circuit - the main operational difference being D1,D1 carry most of the current of M1 and M2 and bias adjustment uses P1 on the bases of Q3,Q4. The Tanaka also has the power transistor b-e junction outside the bias loop and therefore needs thermal feedback to stabilize the idle current.
However, if the ambient temperature is increased
and the power transistors also increase by the same ambient change, then there is a very slight drop in idle current of 1mA for a 10C ambient increase
The attached file includes MOSFET models with tempco's. Notice the MOSFETs are inside the bias loop so they are not sensitive to their temperature changes.
@ Nelson. Thanks for your circuit. It appears there is no feedback of driver transistors in yours, like the Tanaka and ML33.