LM7171 for audio

Leolabs · 24th March 2005, 02:24 PM

If a LM7171 is use for audio application and limited its'bandwith not more than 160kHz,will it:

1)oscillate?

2)produce more noise?

3)sound terrible?

I dont mind any replies even with theory only.All are welcomes!Just try to get some advices.

macboy · 24th March 2005, 07:18 PM

Concerning noise:
This opamp is spec'd at 14.5 nV/sqrt(Hz), which actually doesn't seem too bad for audio use (many audio opamps are less than 5 though). However, when reading specifications, you need to be aware that things are not always as they seem. In fact, the noise of this opamp is higher at audio frequencies (not a surprise since it isn't intended for use at audio frequencies, but up in the MHz range). And not just a little higher... it's at lot higher. See the datasheet for details. In addition to increasing voltage noise at lower frequencies, it also has increasing current noise at lower frequencies too. This is an important consideration since (depending on your input impedances) it can contribute as much or more noise than the voltage noise figure does.
There is a good chance that you will find this opamp to be too noisy for audio use.

24th March 2005, 02:24 PM	#1
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	LM7171 for audio If a LM7171 is use for audio application and limited its'bandwith not more than 160kHz,will it: 1)oscillate? 2)produce more noise? 3)sound terrible? I dont mind any replies even with theory only.All are welcomes!Just try to get some advices.

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24th March 2005, 07:18 PM	#2
macboy diyAudio Member Join Date: Oct 2003 Location: Ottawa, Canada	Concerning noise: This opamp is spec'd at 14.5 nV/sqrt(Hz), which actually doesn't seem too bad for audio use (many audio opamps are less than 5 though). However, when reading specifications, you need to be aware that things are not always as they seem. In fact, the noise of this opamp is higher at audio frequencies (not a surprise since it isn't intended for use at audio frequencies, but up in the MHz range). And not just a little higher... it's at lot higher. See the datasheet for details. In addition to increasing voltage noise at lower frequencies, it also has increasing current noise at lower frequencies too. This is an important consideration since (depending on your input impedances) it can contribute as much or more noise than the voltage noise figure does. There is a good chance that you will find this opamp to be too noisy for audio use.

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