I'm testing out a VCA audio circuit with parts I have laying around based on this article at skullandcircuits.com.
The design calls for a TL072 (datasheet) which unfortunately I don't have on hand.
I'm trying to determine if any of the op-amps I do have on hand from my kit would be compatible enough with the TL072 for a proof of concept.
Dismiss the TDA2822 - it's a power amplifier, doesn't stand the voltage that your rails provide, not pin compatible.
All the others will take the rail voltage. The NE5532, LM358 and JCR4558 are also pin compatible, so could just drop into a socket or board footprint. While you could use the LM324 (very similar to the LM358), you would need to wire it differently. You could use the uA741, and it would work for a proof of principle device, but it's not pin compatible, it's a very old design which is not specified for noise, the output slews like a slug, and it just isn't as good in all departments as newer amplifiers.
The former three all have sufficiently low bias current to work with the bias shown.
- The LM358 has similar voltage noise at 1 kHz to the TL072, and takes 1 mA supply current for two amplifiers.
edit - thanks to frog in comments. The LM358/LM324 has an output stage that's fine for DC, but if used for AC output introduces nasty crossover distortion. This can be alleviated by putting a pulldown resistor on the output to ensure unidirectional output current from the amplifier, see for instance this SO Q/A, but that seems a lot of effort and quiescent current to spend, when you have alternatives.
edit2 - There is a significant difference between the TL072 and your alternative amplifers. The TL072 is a FET based one, so has much lower bias and offset currents, and typically a higher voltage noise and lower current noise. This is where it's important to consider the circuit an amplifier is used in, rather than just comparing data sheet specifications. Given the impedances used in your circuit around the amplifiers, the advantages of the TL072 are not really being used, and the bipolar amplifiers will substitute as well or better.
One of the problems of the 741 was its lack of specifications, and relatively high noise. Although the 4558 says it is 'electrically similar' to the 741, it's clearly not two 741s in a dual package. There is a 3 to 4 improvement in the typical slew rate for instance, always a weakness with the 741. The specified noise for the 4558 is not bad, at 8 nV/rtHz at 1 kHz, only double that of the 'low noise' 5532, and close to the 6 nV of the esteemed OP275. Although the 741 noise isn't specified, if you have ever heard cheap audio equipment from the last century that sprinkled around these newly-usable 741 op-amps, you'll know how intrusively noisy they are.
TL072 is a JFET input opamp, so its main strengths are negligible input bias current and input current noise, and a peculiar input common mode range that is useful in many designs, including this one. This opamp also has a wimpy output stage which distorts heavily should it attempt to drive more than a couple mA into the load.
Total noise contribution from an opamp depends on its voltage noise (specified in nV/rtHz) and how much voltage its input current noise creates across the impedance of the source driving the input.
While "low-noise" FET opamps usually have higher voltage noise than "low-noise" bipolar opamps, when using high impedance feedback and source resistors, current noise will be the more important factor as it will dominate total noise. In this case FET input opamps will offer lower total noise.
In addition, common mode voltage at the output of your multiplier (Q1/Q3) can get pretty close to +12V depending on the control voltage input. TL072 input common mode range includes the positive supply due to its JFET input stage, so it will work fine. Other opamps whose input common mode range does not include the positive supply may not work at all.
This useful feature is due to the threshold voltage of JFETs which allows them to keep the CCS transistor biased and working even if the input common mode is equal to the opamp's power supply voltage:
As the TL072 is an op-amp with FET input stages, it is wildly different from the other op-amps that have BJT inputs.
So none of them are direct replacements as the resistances are so large and more suitable for the TL072. Other op-amps would likely perform poorly in the circuit.
To use another op-amp, you would need to re-design the circuit to support the other op-amps.
Re-design might just mean re-calculating the op-amp gain setting resistances.
But as a side-effect it changes the CV input impedance so you would need to simulate the circuit if it still works within the specs you want it to work.
