Notch Filter Help Needed

[Bill Mountain]

I have a quick question about the notch filter in the attached schematic.  What is the function of tying it in into the emitter of Q2 instead of ground?.  I get that it's some form of feedback but how would it affect the functionality?  Every time I put a bridged-t filter in the feedback loop of an opamp I get a peaking boost at the frequency.   I don't think that's what's happening here because it would no longer be a notch filter. 

Any ideas?

[Bill Mountain]

[Rob Strand]

In this circuit the connection to ground and the the emitter are essentially the same thing because the 47uF in the emitter effectively shorts that point to ground.

That amplifier structure doesn't have feedback, the feedback paths are more for DC.
The way feedback is added to that structure is to place an emitter resistor on Q1 and feedback resistor from the collector of Q2 back to the emitter of Q1.

In google images search for
two transistor tape head preamp

You should read-up on "Q enhancement" .  However I will warn you, beyond the basic idea you will find with a lot of mathematics and circuit analysis associated with this topic.

[Bill Mountain]

Thanks for the great explanation.   This is a big help indead.