There are questions if it matters which type of op-amp is used in the audio amplifier and my answer is that it depends on circuit schematics and op-amp parameters. Some of those parameters are obvious from datasheets, but others may be quite hidden and not clear from the first view. For the test I have chosen well known dual op-amps LM4562, NE5532, LM1458 (bipolar input) and OPA2134, TL 072 (JFET input).
LM1458 is one of the first op-amps usable for audio and it is dated at sixties of the previous century. NE5532 was then a big big improvement in audio op-amps, introduced by Signetics company in 1979. LM4562 appeared in 2006 as an improvement in noise and supposed to have lower distortion than NE5532.
OPA2134 was introduced by Burr-Brown in the nineties as a lower noise and lower distortion improvement of TL072.
As far the datasheet and popular info.
When making a choice of the op-amp, we always need to know the application circuit. For the test I have chosen quite common non-inverting amplifier circuit with +6dB gain and 10k feedback resistors.
The test rig is driven from a DAC with low, 20 ohm output impedance, and loaded with 1 kohm ADC input impedance. This is quite difficult load, but as the output voltage did not exceed 3V, all the op-amps are deep in the area of allowed output current.
Measurements
For the start, I have chosen measurements of THD vs. output voltage at 1kHz and 10kHz and measurements of 13+14kHz CCIF IMD vs. output voltage. The plots are shown below:
We can see that the LM1458 is simply unusable for audio, even at low output voltage and that we can assume it will have its own sound signature. Both JFET opamps, OPA2134 and TL072 have higher distortion than LM4562 and NE5532, in all 3 tests. The result of the old NE5532, that is slightly better than LM4562, is a small surprise to me, I have expected the opposite result.
In all cases, I have tested at least two samples of each op-amp type, to prevent random results. All the samples of the same types behaved identically within the measurement repeatability.
More tests can be done, suggestions welcome. But I will wait for the forum feedback.
All the measurements done with 96kHz sampling and 45kHz effective bandwidth.
Note: for loopback test please go to post #33
LM1458 is one of the first op-amps usable for audio and it is dated at sixties of the previous century. NE5532 was then a big big improvement in audio op-amps, introduced by Signetics company in 1979. LM4562 appeared in 2006 as an improvement in noise and supposed to have lower distortion than NE5532.
OPA2134 was introduced by Burr-Brown in the nineties as a lower noise and lower distortion improvement of TL072.
As far the datasheet and popular info.
When making a choice of the op-amp, we always need to know the application circuit. For the test I have chosen quite common non-inverting amplifier circuit with +6dB gain and 10k feedback resistors.
The test rig is driven from a DAC with low, 20 ohm output impedance, and loaded with 1 kohm ADC input impedance. This is quite difficult load, but as the output voltage did not exceed 3V, all the op-amps are deep in the area of allowed output current.
Measurements
For the start, I have chosen measurements of THD vs. output voltage at 1kHz and 10kHz and measurements of 13+14kHz CCIF IMD vs. output voltage. The plots are shown below:
We can see that the LM1458 is simply unusable for audio, even at low output voltage and that we can assume it will have its own sound signature. Both JFET opamps, OPA2134 and TL072 have higher distortion than LM4562 and NE5532, in all 3 tests. The result of the old NE5532, that is slightly better than LM4562, is a small surprise to me, I have expected the opposite result.
In all cases, I have tested at least two samples of each op-amp type, to prevent random results. All the samples of the same types behaved identically within the measurement repeatability.
More tests can be done, suggestions welcome. But I will wait for the forum feedback.
All the measurements done with 96kHz sampling and 45kHz effective bandwidth.
Note: for loopback test please go to post #33
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