What's current "best" opamp for active filtering?

[sdad]

What's current "best" (maybe 2nd best, if cost is considered) opamp for line level active filtering, audio range? Home application, so standard bipolar +/- 15v supply is good. Either single or dual package good, quad, not so much.

[454Casull]

You'll be hard-pressed to find somebody that can hear the audio signature of an OPA2134.

[Andersonix]

LM4562!

[mbar]

MC33078

Sent from my Milestone using Tapatalk

[Calvin]

Hi,

as usual the answer is...it depends.
In this case it depends on the type of filter and the connected to it parts.
Generally the OP-Amp should not react much to different and varying impedances between their inputs. Gross impedance imbalances may lead to excessive output offsets. An example for such a situation are DC-servos/Integrator where one input sees 0Ohm while the other may see 1MOhm. FET-Input devices are less affected in this regard, because of their much lower input currents. If the source impedances the OPsees exceed ~2kOhms, FET-Input devices may be less noisy due to their much lower current noise. The typical FET-Input candidates are also all low enough in voltage noise for usage in low source impedance circuits.
In most filter applications the bandwidth limit of all OPamps exceeds the requirements by far. Very fast OPamps need more care regarding the power supply lines (hence PCB-layout and associated parts) than ´slower´ devices. So there´s in majority no necessity for fast wide bandwidth parts.
So if You are willing to mix technologies bipolar input OPamps may be suitable certain cases. If You want one device for all a FET-input OPamp should be Your choice.
If cost is a factor FET-devices like OPA604, OPA132, OPA134, or AD711, AD825(featuring a OPamp unusual high OL-bandwidth of >10kHz) and bipolars like the NE5534 or NJM4580 and their Dual and Quad brethren are suitable.
If cost is no object FETs like BB/TIs OPA627, OPA827, AnalogDevices´s AD743, AD8610 come to mind as well as the bipolar AD797 and some of the LME-Series of NationalSemi.

jauu
Calvin

[EUVL]

> If You want one device for all a FET-input OPamp should be Your choice.

My choice in any case.
With modern FET input opamps, the noise advantage of BJT opamps becomes insignificant at line level.

> If cost is no object FETs like BB/TIs OPA627, OPA827, AnalogDevices´s AD743, AD8610 come to mind ...

You should try something modern like the OPA1641/2 for FET and OPA1611/2 for BJT.
And they are not even expensive.


Patrick

[EUVL]

If I were to use a Sallen Key with no gain, I basically only need a follower.
In such cases, I shall definitely use a pair of JFETs such as 2SK372 or 2SK369, as in :

A Compact, High-Performance Source Follower Module


Patrick

[abraxalito]

NE5532 is best bang for the buck by a long way, so long as you're not asking for gain as well as filtering. If you are, then something with a bit more GBW would be appropriate - perhaps LM4562.