02-11-2021, 08:36 PM
The TL06x is widely used in audio stuff powered by phantom power (e.g. DI boxes and the occasional condenser mic) - hard to argue with only 200uA per section! The distortion is about twice as high as the TL07x in the circuits I've tested, but still more than adequate. Not the quietest, but not a bad compromise given the power draw.
Funnily enough, the TL072 doesn't seem to be any quieter than the TL08x, at least according to the datasheets. Perhaps that wasn't always the case? But then you wouldn't choose a FET op-amp in a typical low-noise design, unless the source impedance was unusually high (by audio standards). The OPA2134 is a good replacement for the TL072 if you need a FET op-amp but want to keep the noise down. The NE5532 generates about half the Vn again, but obvious makes a bit of In.
The common-mode problem is fun. When both inputs get within a couple of volts of the negative rail, they swap their polarities, usually causing horrible rail-to-rail clipping. It's mostly a problem for unity gain followers and similar circuits - not an issue for circuits with gain or inverting stages. Not a good op-amp to use as a comparator! A former colleague of mine fell for that a long time back, which surprised me at the time, but it's easy to forget, I guess. Swapping out the TL084 for an LM324 or similar fixed it (it didn't need to be a FET op-amp, it was just what he had lying around).
I keep thinking that I should find a modern equivalent for the TL06x ICs, but that combination of reasonable audio performance, high supply rails (+/-15V, though the TL07x and 08x will do a bit more) and, crucially, low current draw is hard to find, especially at sensible prices. Though at the moment the DIL versions are about a quid each from Farnell. RS are a bit cheaper, but have no stock (and have stopped predicting when they'll get some).
Funnily enough, the TL072 doesn't seem to be any quieter than the TL08x, at least according to the datasheets. Perhaps that wasn't always the case? But then you wouldn't choose a FET op-amp in a typical low-noise design, unless the source impedance was unusually high (by audio standards). The OPA2134 is a good replacement for the TL072 if you need a FET op-amp but want to keep the noise down. The NE5532 generates about half the Vn again, but obvious makes a bit of In.
The common-mode problem is fun. When both inputs get within a couple of volts of the negative rail, they swap their polarities, usually causing horrible rail-to-rail clipping. It's mostly a problem for unity gain followers and similar circuits - not an issue for circuits with gain or inverting stages. Not a good op-amp to use as a comparator! A former colleague of mine fell for that a long time back, which surprised me at the time, but it's easy to forget, I guess. Swapping out the TL084 for an LM324 or similar fixed it (it didn't need to be a FET op-amp, it was just what he had lying around).
I keep thinking that I should find a modern equivalent for the TL06x ICs, but that combination of reasonable audio performance, high supply rails (+/-15V, though the TL07x and 08x will do a bit more) and, crucially, low current draw is hard to find, especially at sensible prices. Though at the moment the DIL versions are about a quid each from Farnell. RS are a bit cheaper, but have no stock (and have stopped predicting when they'll get some).
