It is intended to drive headphones with low distortion, and be driven by fairly high impedance source (~500R).
The trouble is maintaining a very high input impedance with high quiescent current, the values for a voltage divider needed to create a 'stiff' bias voltage (10 times the base current) on the base are quite low, the values in the schematic are already assuming a generous Hfe of around 200.
I think the CCS helps with this, with the bias current remaining constant with changes in emitter voltage, so only current to the actual load will affect beta So instead the divider could be sized to 10 times the peak load current which is much lower... Correct me If I'm wrong on anything.
I'm wondering what the effect on the ratio between the divider and base current (or in this case load current divided by beta) has on the output signal (distortion etc.)?
'1/10th' seems to be just a general, minimum figure and may not be ideal choice for this..
While the CCS may allow to use higher values in the divider and still have 1:10 ratio, it could also let me use a higher ratio (e.g 50:1) using lower divider values for a bias voltage.