Electronic – emitter follower biased by input signal

emitter-follower

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For the standard emitter follower you typically need input coupling capacitors and a DC bias of roughly half the supply voltage however what if the input signal itself swings around half the supply voltage?

e.g if the previous stage to an emitter follower is a standard op amp non-inverting amp with a split supply (+12V,-12V) with the input referenced to centre point but the succeeding emitter follower is referenced to -12V (i.e +24V, 0V),
so The op amp output is referenced to ''+12v'' relative to the emitter follower?
Could this replace the input coupling cap and resistor biasing or would it not work?

Load would be a pair of headphones (50 to 300 ohm)

example of circuit is attached below

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Differential emitter follower?
differential emitter follower

Inverting amp?

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Best Answer

Could this replace the input coupling cap and resistor biasing or would it not work?

A more convenient idea would be this: -

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It's called a DC coupled amplifier and uses feedback directly from the emitter to set the gain at the output to be: -

$$1 + \dfrac{R2}{R1}$$

Of course, if you really want the return current for your headphones to go via -12 volts (potentially noisier) then you will need an output capacitor.