So .. this kept bothering me, so I just put a simplified thing into that online circuit sim...With all defaults in the sim (except bumped the beta a bit just in case), this thing actually gives: 32uA and 31uA as the collector currents, with 63uA total over the 150k, which is basically balanced with bases at -6.4mV and -7.2mV. With "spice-default" instead of "default" for the transistors we have about 33uA vs. 28uA which is still pretty close to balanced.Likely did not care or omission. 1:2 is not terrible imbalance, relevant for high fidelity mic preamp or poweramp, not here.Oh, you're probably right... I must have had a brainfart thinking there was some sort of a voltage divider... though that still doesn't answer why the odd values for what seems like just feedback.
Any idea though why the asymmetric bias though? For gain?
I don't know. The fact that the two transistor models in the sim disagree to a certain extent suggests it could be a case of "doesn't seem like the math is works out here, let's tweak.. oh right now it's closer" and the design is actually nowhere near as imbalanced as it might seem. Or it could just be that this poor sim is not realistic enough.
Statistics: Posted by mystran — Fri Feb 16, 2024 4:08 am