How much is the gain?

[richardjhy]

Hi Newbie here. Can anyone help me figure out the voltage gain after IC620 and why C703 and C704 are there? Thanks.

 

[rayma]

Do you mean the voltage gain OF the op amp circuit?

The capacitors reduce the gain to unity at DC.

 

[richardjhy]

Does it mean that the gain is variable within the range of audio frequency? I thought that for a given op amp circuitry the gain should be fixed.

 

[rayma]

Op amp circuits can certainly have variable gain.
Where does this circuit come from?

 

[stocktrader200]

Looks like a tone control and low cut filter.
Expect about 20db gain controls flat.

 

[BSST]

As rayma indicates, the opamp has unity gain at DC to establish its bias. At mid audio frequency the gain will be about R741/R739 + 1 or about 392.7 = ~ 52dB.

 

[cbdb]

Not that simple. There’s a nested FB thru R725 and some feedforeward?? from R733

 

[rayma]

The R733 appears to be for Sallen-Key HP (rumble?) filter.
This is combined with the FB tone controls.

 

[BSST]

Not that simple. There’s a nested FB thru R725 and some feedforeward?? from R733

That's true, but I did say "about" and still believe estimate is close. 😉