[MN Ham Phones]

Forgive my OP Amp ignorance, but if unacceptable DC offset levels were measured, what can be done about it besides not engaging bass boost?

 

[ppl]

Use a Precision op amp like the AD-8610 or OPA-627

 

[amb]

If you're using an op amp with bipolar inputs instead of FETs, somewhat higher offsets can be expected. If the offset is less than 10mV then it's nothing to worry about. I don't know which amp design you are working with, but you can add an offset nulling circuit if absolutely necessary. Basically, use a multi-turn precision pot that's tied to the V+ and V- supplies on both ends through resistors, and feed the wiper to one of the op amp's inputs. Adjust the pot until the output is 0V DC.

Something like this:

This all assumes that your op amp is running a split power supply or single supply without a virtual ground. Otherwise the offset will be one-half the supply voltage and you must use a DC blocking output coupling capacitor.

-Ti

 

[MN Ham Phones]

I will be using 8610s in a PPA design straight from Tangent's pages.
I figured the 8610 was "quality" but just didn't know when/why offset occured.

Thanks all for the info.

 

[tangent]

Quote:

just didn't know when/why offset occured.

If you get high offset with a precision part like the AD8610, something's wrong with the circuit. Virtual ground could be misbehaving, the ground channel could be broken, one of the channels could be oscillating, etc.

If you get high offset with a non-precision part, you'll just have to try different units until you get one with low offset. Offset is partly a manufacturing variation (imperfections in the parts) and partly due to the way the device works interacting with the circuit (offset currents, etc.)