Can you please reveal us where you found the schematic. I'm curious who's the designer.
My simplified has a sensitivity vor mains voltage.The difference between the current in R1 and R3 should be very small.
The original circuit is better as the balance is guaranteed through the current mirror.
But we can switch positive and negative half to get something like this. It is still rail to rail.
Now we have stable quiscent current in a fast stage with high bandwith and low distortion.
We can drive it with every VAS and use the nonswitching output that Ian Hegglun revived.
The original circuit is better as the balance is guaranteed through the current mirror.
But we can switch positive and negative half to get something like this. It is still rail to rail.
Now we have stable quiscent current in a fast stage with high bandwith and low distortion.
We can drive it with every VAS and use the nonswitching output that Ian Hegglun revived.
In the original circuit the idle current is set by R22 and 23. They get about 800mv so the current there will be about 17uA.
The output stage amplifies about 910/0,33 = 2757. That gives an idle and minimum current of about 47 mA. I believe R25 and 34 is only there to adjust DC unbalance in VT17, 18 and VT27, 28. When i tested the output stage it seemed pretty unsensitive to idle current. Worked for me down to 2 mA.
I think VT12 and 15 are thought to have practically 0 idle current. Othervise R22 and 23 would be unnecessary.
The output stage amplifies about 910/0,33 = 2757. That gives an idle and minimum current of about 47 mA. I believe R25 and 34 is only there to adjust DC unbalance in VT17, 18 and VT27, 28. When i tested the output stage it seemed pretty unsensitive to idle current. Worked for me down to 2 mA.
I think VT12 and 15 are thought to have practically 0 idle current. Othervise R22 and 23 would be unnecessary.