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Inverting opamp cct ...blocking cap? - help!
Inverting opamp cct ...blocking cap? - help!
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Old 28th March 2009, 10:05 AM   #1
HankMcSpank is offline HankMcSpank  United Kingdom
diyAudio Member
Join Date: May 2008
Default 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)...is 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...

http://tinyurl.com/crylhw (fig 6).

I'm sure the datasheet wouldn't be wrong...so what am I missing?
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Old 28th March 2009, 10:24 AM   #2
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
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.
regards Andrew T.
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