Getting started with active crossovers (1 Viewer)

[Michael R Price]

There are a million different kinds of opamps, and it really depends how much you are willing to spend and what kind of sound you want. I don't know too much about them but I have used NE5532s and OPA2134s with good results. I never did any reliable opamp sound quality comparisons, but there is a lot of information available and everyone has a good reason to recommend one or the other.

With opamps that use bipolar input transistors, there is a small error current drawn through the input terminals that you can balance out with extra resistors. This may be what you mean by "biasing." If you use a single supply then you need to "pull up" the input to half the supply voltage and add a capacitor on the output. Also, it's possible to force an opamp into class A bias with a resistor to a voltage rail, but that is sort of pointless.

 

[Mike Keith]

I like BB OPA 2134's as well, their stable and resolute, but a bit noisy, a good compromise. I'm actually learning some things from Michael R Price’s post, nice to the point synopsis of balance technique, I understand it better now.

Thanks.
KD

 

[ThomasW]

Here are the spec sheets for the OPA2604 and the OPA2134

Somehow I doubt that the difference between 0.0003% and 0.00008% distortion is all that audible.

The higher slew rate combined with the wider bandwidth and the ability to drive 600 ohm loads, makes the choice of the OPA2604 a no brainer for me .....

 

[Scott Simonian]

What does an opamp do?

 

[Michael R Price]

Scott, it is a differential input signal amplifier with extremely high open loop gain, where you control the feedback with external resistors. In the case of active crossovers the negative input is usually just connected to the output, giving a gain of 1... the op amp is used as a buffer between stages so that the impedances do not interact as they would in a passive crossover.