AMZ Frequency Booster

[sbirkenstock]

Hi Everybody,

can somebody help me understand how this works?
I am not clear if there is positive feedback (output OpAmp back to non inverting input) or
if the signal that is taken between C1 and C2 is working on the negative input of the OpAmp.
In other words, is the contact between C1 and C2 an "input" or an "output"?
Or any other explanation?
What is the flow?

Thanks a lot,
Stephan

[PRR]

It is two parts: a Bridged Tee filter, and an amplifier.

The Bridged Tee is old but had a fad after a 1951 paper, then again when amplifiers got cheap and that variation's analysis got around.
http://tf.boulder.nist.gov/general/pdf/2526.pdf
https://sites.google.com/site/garydavenportelectronics/home/bridgedtnotchfilter
http://www.muzique.com/lab/notch.htm
http://www.geofex.com/article_folders/eqs/paramet.htm

The basic ploy is a notch. However the plan you posted sounds like a boost; also the Rs and Cs are swapped. Too late to work out the difference.

[Mark Hammer]

Good catch and nice concise explanation. 

The unit will go into oscillation when the 5.6k+10k resistance goes much beyond that range.

The boost is cancelled when the ground leg of the op-amp is lifted.  Jack Orman shows it connected to ground through a 10uf cap.  The original schematic shows the 10k resistor connected directly to Vref, minus the 10uf cap.  Both work.