I just cheked my order it is for OPA1688DR which apparently is indeed a SOIC. It's sometimes confusing (for me at least) which package is which code.
Jan
All the 32ohm load specs in the OPA1688 datasheet are based on +/-5V.
But probably more than enough for an Autoranger.
Patrick
Yes I would look to something like 600 ohms at 1V. The OPA2134 shows increased THD at higher frequencies with 600 ohms.
Jan
Could be. They don't show THD at higher load resistances. And the supply is limited to +/-12V meaning I cannot just drop it in.
Jan
Jan,
At 600 Ohms load the LM4562 LM4562NA/NOPB Texas Instruments | Integrated Circuits (ICs) | DigiKey has much better noise and distortion performance than the OPA2134. The LM4562 comes in the 8DIP package that you can swap in and out of the socket on your PCB. Click on the link above for Digikey quantities available and prices.
DT
I've looked at the 4562 earlier but had issues with offset in my particular circuit. And it was not as good as the '2134.
See attached.
Jan
Jan,
Single Op-Amp (i seem to recall that a single op-amp is needed)
AD797ANZ Analog Devices Inc. | Integrated Circuits (ICs) | DigiKey
Very low noise
Very low distortion
Very low voltage offset
Very expensive
DT
Single Op-Amp (i seem to recall that a single op-amp is needed)
AD797ANZ Analog Devices Inc. | Integrated Circuits (ICs) | DigiKey
Very low noise
Very low distortion
Very low voltage offset
Very expensive
DT
High Z circuits with imbalanced feedback impedances are quiet sensitive to input bias. Low noise gets you to this place. The best might be the LME 49880 but I believe that's history. Some Opamps are better at input bias cancellation. I may be able to roll through an assortment and see what happens. More responsible is to work from the specs instead of hand picked samples.
Sent from my LG-H811 using Tapatalk
Sent from my LG-H811 using Tapatalk
Scott would be the best input on bias cancellation circuits.
For what its worth in a practical example, on the Boonton input the original design used NE5532's as the input buffers and needed a separate circuit to handle the DC measurement loop. Swapping to LME49710's allowed for removing the separate DC circuit since the bias and offset were low enough to get good results. Mike Lynch (the original designer) confirmed these to me. The datasheet says 7 nA typical, 72 nA max. Its possible an LME49720 could work. I'll try several options and look at DC on the output.
Most soundcards block DC. Many ADC's have an internal selectable DC block. The question is how much DC offset before the performance of a soundcard is compromised.
I guess a valid question is whether the input needs to be DC coupled.
For what its worth in a practical example, on the Boonton input the original design used NE5532's as the input buffers and needed a separate circuit to handle the DC measurement loop. Swapping to LME49710's allowed for removing the separate DC circuit since the bias and offset were low enough to get good results. Mike Lynch (the original designer) confirmed these to me. The datasheet says 7 nA typical, 72 nA max. Its possible an LME49720 could work. I'll try several options and look at DC on the output.
Most soundcards block DC. Many ADC's have an internal selectable DC block. The question is how much DC offset before the performance of a soundcard is compromised.
I guess a valid question is whether the input needs to be DC coupled.
Yes good question. The AR has input AC coupling but the output to the soundcard is DC coupled, if only to save on a couple of potentially expensive caps. But it's a thought.
Jan
Found this one
Feel free to swap out the OPA1688 for the OPA2172 if you like. Since the 2172 is a bit more expensive you'll be helping us outI admit that I was the applications engineer at the time that had been playing with the 2172 and figured out it made a nice little headphone amplifier. I proposed that we put it in the 3mm x 3mm DFN package to support portable audio applications and the project was off and running.
It was initially a resymbolization but we did change some of the test limits in production (input offset voltage limits are a bit wider) and added some more audio specific characterization to the datasheet. I wouldn't have liked this to be printed on the bag, but these things happen!
My friend Wisse was here last week and recorded a video with me waxing lyrically about the AR
My aim was to give a good run through what it is and what it does.
Feedback appreciated.
Autoranger video
Jan
My aim was to give a good run through what it is and what it does.
Feedback appreciated.
Autoranger video
Jan
DT, I might later this year. I am collecting interest to get to a sizeable order to keep it affordable. You are on the list now
Jan