This is a Shunt Series Pair Wideband Amplifier circuit. This circuit has four feedback loops, they are two emitters feedback, shunt-shunt feedback and an AC feedback loop(series-shunt). This is a very stable circuit and can be used for wideband amplifiers and low gain. This circuit requires +12 supply that restrict the “headroom” of the second resistor. The emitter of the second transistor feed the a shunt-shunt feedback resistor whose upper end that can give more current without causing a grater voltage drop in the collector resistor. Here is the schematic diagram of the circuit:

Shunt Series Pair Wideband Amplifier circuit schematic

Beside shunt-shunt feedback, this circuit has an AC feedback loop(series-shunt). The DC bias is blocked by 0.1uF capacitor. The amplifier has gain of about 12 if AC feedback loop is removed. AC feedback loop’s gain is 2.8, so this circuit has gain of 3.16. At 1Khz, the gain of this circuit is 3.11. Be careful large loop gains are dangerous at high frequencies. [Circuit’s schematic diagram source: Elizabeth R. Tuttle]