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pearltorto Posted - Feb 24 2009 : 7:31:32 PM
Hi I'm using this op amp with 4 741 op amps inside. the first is for an amplifier, the second is for an active peak detector, and now i'm trying to get another amplifier (non-inverting) for the third op-amp, but at this point the circuit stops working altogether. Would it be because the fourth one is unused or something?
The op amp data sheet is here if that helps;
http://www.datasheetcatalog.org/datasheet2/9/0oa8seftq8d6peigox0lrx6e9wwy.pdf
3   L A T E S T    R E P L I E S    (Newest First)
pearltorto Posted - Mar 06 2009 : 1:05:54 PM
never mind
audioguru Posted - Feb 25 2009 : 08:36:12 AM
Since you didn't post your schematic then we can't see if it is correct or if the wrong pins numbers were used.

A lousy old LM324 is not four lousy old 741 opamps:
1) The LM324 quad opamp is low power so its bandwidth is low (2kHz at full output voltage) and it has up to 3% crossover distortion. The LM358 is the same but is a dual opamp in an 8-pins package.
The 741 opamp has "normal" supply current, a bandwidth up to 9kHz at full output voltage and has low crossover distortion.
2) The LM324 has PNP transistors at its inputs that work fine at the negative power supply voltage.
The 741 opamp needs its input voltages to be at least 4V above the negative power supply voltage.
3) The LM324 has outputs that go down to the negative power supply voltage.
The 741 has outputs that go as low as 1.2V above the negative power supply voltage
They are both too noisy for audio amplifiers.
pearltorto Posted - Feb 25 2009 : 07:59:48 AM
oh if it helps, i moved the third amplifier to the fourth op amp and it works. its the same for another one too

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