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HankMcSpank 28th March 2009 10:05 AM

Inverting opamp cct ...blocking cap? - help!
I'm wanting to use a little chip that has AGC built in, here's the datasheet...

It's stereo, and uses a basic opamp circuit with negative feedback at its inputs. My query relates to the diagram called 'test & application circuit' on page 4 in that link above.

Specifically the cap C1 (or C8...depending which input you look at) that right? It would appear to be a DC blocking cap in the negative feedback path?

Again, here's a cctwhere someone uses this particular chip...again a DC blocking cap in the negative feedback path....

What am I missing here? I always thought a basic inverting opamp needs to have a DC path back to its inverting input, for example... (fig 6).

I'm sure the datasheet wouldn't be what am I missing?

AndrewT 28th March 2009 10:24 AM

the circuit shows audio input to the non-inverting pin.
The two input pins need a resistive load to take input offset current.

Maybe the simplified IC diagram fail to show an internal resistive route for the offset currents.

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