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I was ordered about 400pcs of these chips in SO8 package from Farnell and from Digikey within some years period. I am using these chips for ultra low distortion audio range sine oscillators manufacturing. But, I need to make noise spectrum measurement control before trying these chips, because situation is non understanding for me in frequency region lower than 100Hz. Only approximately half of all chips has noise density in this region similar as in higher frequency region, but approximately 20% of all chips has very high noise and flicker (more than ten times higher) in this low frequency region. In other ways these chips are very nice, and allow to build oscillators with distortions level about -150dB at 1kHz.
Thank you,
Victor.
Hi, Andy.
Please advise, if you can, that observed situation is normal, or maybe something is wrong.
Thank you.
Hi,
Here are some pictures of spectrum measured in same conditions.
1) very good chips (around 50% of all quantity):
2) good chips (around 30% of all quantity):
3) Noisy chips (around 10% of all quantity). Two pictures from different chips)
4) Very noisy chips (around 10% of all quantity). Three pictures from different chips:
Last chip measured in wider frequency range:
Hi Victor,
In my opinion, if you really care about the "excellent performance in all audio range", I suggest you do the screening by yourself. Sorry, it is not a very good answer, but I cannot offer you a better one.
Andy
I am also seeing burst noise in various production lots of the DIP LME49720 and LME49860. This was observed at the output of a 40 dB gain instrumentation amp input. The NJM5532, NJM2114, NJM2068 and MC33078 do not exhibit this burst noise in the same circuit and same PC board.
It sometimes takes several seconds to occur so if the test time is short, parts with this defect are not screened. This LME49720 sample was a brand-new from the tube lot JR18ABE3.
Thanks David and Victor for bringing this back onto radar. Since the LME49710, LME49720 aka LM4562 etc. have been brought back to life on an 8" fab I have to wonder if the stock that's exhibiting the 1/f and burst noise is new or old.
Any indication Victor when and where your 50 were made?
I've got a circuit right now on the bench where I'm comparing the NE5532, NJM2114, OPA2134, OPA2604, OPA1642, OPA1612 and the LME49720. The circuit is not particularly critical as to whether it needs to be FET, bipolar or low Ib. Bandwidth, drive current and THD are the relevant parameters. Until I reluctantly tried the LME49720 (due to the LF noise and sourcing issues) the OPA1612 performed best. Glad I revisited the LME49720 because it outperforms all of them on distortion. The OPA1612 is a very close second and if it were available in through hole it would be my first choice because its very, very quiet with a smooth-sounding, not rocky, noise floor.
I've recently used the OPA1612 in both a Moving Coil preamp and a Mic Preamp (both using external transistors on the front end) and they were very, very quiet. (The MC preamp used ZTX851 transistors the Mic preamp THAT300s.)
Also compared the OPA1612 to an NJM2068 and OPA2134 in a moving magnet preamp and it was, as expected due to higher current noise, noisier than the BJT '2068 and FET '2134. The outcome was no great surprise but the noise character of the OPA1612, which was exaggerated due to the current noise and inductive source impedance, was still clean-sounding noise. In the same circuit the LME49720 (and the LME49860 RIP) were unusable due to burst noise.
The OPA1612 does not seem to have the process contamination of the LM497X0 that produces rocky-sounding noise.
I have not tested the OPA1612 with high value bias resistors to see if it has the latch-up/bias current correction start-up issues of the LME49720.
In terms of noise performance in the real world the OPA1612 beats the LME49720.
As I know, OPA1612 isn't better for my application. Also, according the data sheet, OPA1612 may has higher input bias current, and has no data for to drive 600 ohm load. And finally, OPA1612 is more expensive.
Thank you for the link Victor.
"[OPA1612] has no data for to drive 600 ohm load."
The 600 Ohm THD load data is featured on page 1 of the datasheet and also characterized on page 8.
The OPA1612 does have a higher maximum Ib. The advantage of the OPA1612 in my experience is that you don't have to throw 20% or more of them away due to noise. So they may not be as expensive as they appear to be.
100% of my limited supply of LME49860 and LME49720 over several different dates codes have burst noise in high gain circuits. I would not enjoy screening SMT parts.
That is exactly the type of burst noise I saw in earlier (6") production runs of the LME49720.
I bought a few from Mouser some time ago that were clean but I don't have any recent lots to test.
TI really needs to get some of your parts back to do failure analysis. I would return them to the distributor for credit, replacement or reimbursement. Those parts will go back to TI and they can start looking at this.
Finally the Mouser accepted the return. Thanks Mouser for this.
Last week received 100pcs of the LME49720 ordered from TI store. Country of origin marked as Philippines. After the test I have 23 noisy parts. Asked TI store for the return. Waiting for the answer.