This is a set of measurements of 19+20kHz IMD distortion of the following opamps: AD4627, ADA4898, AD8597, OPA140, OPA141, OPA1641, OPA209, OPA1611, OPA637, NE5534. Measured at non-inverting gain 40dB and 3.4Vp-p output.
Output load?Supply voltage/s?
+/-15V?
That's why I asked for a loopback, I wouldn't expect those products, especially at exactly the same level in each plot.All of your graphs show something at 8, 9 and 10 khz. Is this an aliasing/imaging product from using digital test gear? Looks like you used a 32 k FFT and 48 khz sampling.
Thanks for doing and sharing this btw. Good info.
The measurements were done in January 2013. I may try to re-arrange the system, but I am not sure if I can replicate it perfectly. 2nd issue is that the DUT had 40dB gain so the DAC output is small and less distorted than if it works in loopback without gain. My guess is that the system distortion limit was close to OPA637 result.Can you post the loopback of the measurement system?
All of your graphs show something at 8, 9 and 10 khz. Is this an aliasing/imaging product from using digital test gear? Looks like you used a 32 k FFT and 48 khz sampling.
Thanks for doing and sharing this btw. Good info.
May you consider to use the new TI OPA1656 as "SoundPlus™ ultra-low noise and distortion, Burr-Brown™ audio operational amplifier"
I'm surprised that the "ancient" NE5534 apparently does so well.
I'm surprised that the "ancient" NE5534 apparently does so well.
I think it was intended for audio applications from the start, so it makes sense that its DC performance was not what was required for instrumentation applications. If I remember correctly, it had compensation pins which were of use in particular instances. I know of one engineer who used these pins to optimize the audio performance for his particular application. The NE5532 (basically a dual NE5534 internally compensated) is still used, which I find interesting.Not really, it was the first op-amp (?) that compromised DC precision for audio applications. It has almost no use in precision instrumentation where drift, offset, and bias current issues are important. Just an historical observation that the money in the 60's and 70's was in military and aerospace applications.
An opamp in a science experiment dropped off by some moon walkers...
http://www.righto.com/2019/02/op-amp-on-moon-reverse-engineering.html
Hence why the NE5534 was looking particularly good - output driving is more than decent, and the part's potential issues with common-mode distortion (though less pronounced than 5532) are not being highlighted. IMHO this part was the best single-chip compromise (voltage noise, current noise and output driving) for an MM phono stage for many years... I think it takes something quite recent like an OPA1656 to upstage it even in this application... truly low-noise FET parts have never been too common (the AD743 comes to mind, but that's not exactly super fast, and at 18-20 pF of input capacitance I don't dare asking what common-mode distortion is like).