Re: op amp basics
zeerum,
Suppose v1 and V2 are equal positive voltages. If v1 increases, the current through R1 increases, causing the collector voltage to decrease (out of phase output at the Tr1 collector). At the same time, the emitter voltage on both transistors increases due to the increase in emitter current thru Tr1. The result is that the base-emitter voltage of Tr2 is lower (less positive) than it was, causing the collector current thru Tr2 to decrease. This results in an increase in vout (in phase with the input).
Regards,
Kral