Active Audio Filters

[iceblue]

I need to build some active audio filters and was just wondering how important the actually op-amp choice is. Is it best to go for an opamp recommended for audio purposes or would general purpose ones suffice?

 

[MRCecil]

As far as selection of the op amp goes that depends on the frequency, the Q of the desired filter, the gain bandwith product, etc. Here is a design application that can provide a big step up and a real time saver to active filter design:

Active Filter Design Application - FILTERPRO - TI Software Folder

 

[atferrari]

I know you did not ask for this but just in case you could also consider:

**broken link removed**

 

[iceblue]

Thanks. Can't install the TI software as I have a problem with my .NET Framework installation. Waiting for IT dept to come sort it out. I looked at the one from Microchip in the meantime. Quite useful.

The filters will be approximately 120Hz LPF and 100Hz HPF all with unity gain.

 

[crutschow]

I need to build some active audio filters and was just wondering how important the actually op-amp choice is. Is it best to go for an opamp recommended for audio purposes or would general purpose ones suffice?

Audio op amps are designed to have lower noise and cross-over distortion than general purpose op amps. So it depends upon how important noise and distortion are in your application.

 

[audioguru]

A lousy old 741 opamp was called "general purpose" 42 years ago when opamps were not used for audio.
It has trouble above only 9kHz so it misses more than half of the frequencies of audio. It has a lot of hiss.
It might be OK for telephone-quality audio or an AM radio. "Wa' did you 'ay?"

 

[iceblue]

Ok so ruling out the common 741, 358, etc would a precision op-amp be any better or should I just go straight for one marketed as an audio op-amp? Noise and distortion need to be low. The proper audio op-amps are significantly more expensive than the other options and since I will need quite a few I want to keep costs to a minimum.

So right now I am thinking of just going for the audio ones, unless someone thinks a precision op-amp will do?

 

[audioguru]

You don't need a precision opamp. You simply need an audio opamp that is not 42 years old. They are low noise, have low distortion and have full output up to 100kHz. A TL072 dual audio opamp costs almost the same as a lousy old 741 single opamp.

Why are you chopping off the bass frequencies?

 

[iceblue]

Thanks. That one looks like a good option.

I'm basically creating an active cross over. So the bass will be going to the subwoofer and the rest of it to the speakers.

 

[audioguru]

A TL071 is the single opamp version of the TL072 dual and the TL074 is a quad.

 

[iceblue]

Yeah, thanks. Will be getting some TL074's.