Hi, Im working in a microphone preamplifier using the classic instrumentation amplifier topology, but modified for linear gain control, I am really happy with the results as the circuit is very quiet and rejects RF and power line noise (at least for my application).
I am very confused regarding NPN BJT op-amp's (like the NE5532) input bias current compensation, I've read many datasheets and some books, but I still dont get it.
I am planning to use any of these op-amps NE5532 or LM833, (currently using LM833's with DC input bias current path to ground through resistors) the reason is that Im currently living in a country where most recent op-amps are unavailable (like OPA2134 or INA217, etc).
My main questions are:
If I use the NE5532 as the main op-amp in place of LM833 what is the most simple input bias current compensation?
What op-amp do you think is more suitable for this application NE5532 or LM833? (those are the only audio op-amps I can find here)
I apologize for my bad english, thanks in advance.
- Marc Fricke
I am very confused regarding NPN BJT op-amp's (like the NE5532) input bias current compensation, I've read many datasheets and some books, but I still dont get it.
I am planning to use any of these op-amps NE5532 or LM833, (currently using LM833's with DC input bias current path to ground through resistors) the reason is that Im currently living in a country where most recent op-amps are unavailable (like OPA2134 or INA217, etc).
My main questions are:
If I use the NE5532 as the main op-amp in place of LM833 what is the most simple input bias current compensation?
What op-amp do you think is more suitable for this application NE5532 or LM833? (those are the only audio op-amps I can find here)
I apologize for my bad english, thanks in advance.
- Marc Fricke
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usually, input bias compensation is accomplished by using the same input resistor values for both inverting and noninverting inputs...... in other words, if you have a 1k resistor to ground from your inverting input, you place a 1k resistor in series with your noninverting input. with most modern opamps and low to medium gain (2 to 500) it's not really an issue anyway. input bias currents really become a problem at high gain.
since the gain of this preamp is so low, and it's also ac coupled through a cap, it's nothing to worry about.
since the gain of this preamp is so low, and it's also ac coupled through a cap, it's nothing to worry about.
Then I realized that it was impossible it was not working with the power supply if it already worked with batteries, so I went to a lab where I used a expensive bulky PSU unit to feed the circuit and it worked really well, with the exception of some channels that had some low freq hum.
That is my main problem right now, what is causing that?
That is my main problem right now, what is causing that?
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