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Op amp input level

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3/2/2000 1:08 AM
John	Op amp input level WHAT IS THE HIGHEST DB AN OPAMP CAN TAKE BEFORE DISTOTION?

 

3/2/2000 1:40 AM

Don Symes

Depends on the power rails and the gain setting.     You can take the inputs to within a few millivolts of the rails on good, modern op-amps. Older, junky ones like the 741 can't get closer than a couple of volts.     The next consideration is the gain. You can't get the output to swing beyond some specific point, so it's easy to get the output to clip if you set the gain too hihg.     Sorry, but you'll have to convert these ravings to dB... I juszt can't keep that straight.     Good luck!

 

3/2/2000 1:50 AM

R.G.

"db" is a power ratio, not a measure of power. A "db" is always referenced to something. In most cases for audio, it's referenced to 1milliwatt into 600 ohms, often called a "dbw". A signal of 1mw into 600 ohms then becomes 0db, and you can scale from that. But there are other references. A db is just a relative ratio.     As to the signal level an opamp can do before distorting, it depends on the power supply the amp runs from and the feedback/gain conditions the opamp is run under. An opamp (or any other amplifier) will clip when the input signal times the closed loop gain exceeds the power supply limits.     Opamps are usually designed to have some minimum gain before feedback reduces it - this is often over 100db (that being a ratio, it's a correct usage). Since a gain of 10 is 20db, 100db is 10 to the fifth power, or 100,000. Gains over several million are not uncommon at all.     If an opamp is run from 9Vdc and is used open loop (no feedback), the the signal that causes it to exceed the power supply limit can be as small as 4.5V/1,000,000 or   a few microvolts. If the opamp is set up with a closed loop gain of 10, then the signal level that makes it clip is 4.5V/10 or .45v     It all depends. You might want to read a book from your local library on electronics and opamps. There is undoubtedly a good selection there.

 

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