As I am a new user I cannot access the archive to check my TMS3 upload! Unfortunately, when I scanned it, I didnt save my own copy! To save scanning again, can someone have a look and see if the text and circuit diagram is reasonable enough to view without fades or blurs?
Thanks, Rob
Hi Rob,
Thank you for all of those uploads - I hope people appreciate all the effort you've gone to.
I couldn't immediately spot the TMS3 (could see 1 and 2), so if you have a link to the post, I'll gladly check it out.
You're on 14 posts, so if you reply to this, that'll make 15 and you'll be able to access them yourself
Thanks once again,
Mark
Ah - just found it:
https://golbornevintageradio.co.uk/forum...p?tid=8595
It looks fine to me. Just looking at the schematic, I'm seeing a TL083. Of course, I know about the TL081, 082 and 084, but the 083 is either new to me, or I've forgotten about it. Looks like a dual in a 14 pin package, perhaps. Google draws a blank. Interesting...
I've used loads of TL081, TL082, TL084 over the years but not sure that I'd ever even heard of TL080, TL083 or TL085. I am now suitably enlightened.
Not forgetting the low power TL06x and low noise TL07x parts.
None are especially outstanding opamps by modern standards but they are dirt cheap, unfussy, good enough for may jobs and readily available. ISTR the input stage can play nasty tricks on you if you take the inputs to the -ve rail and beyond.
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).
Thanks! 15th post!
Will see if I can access it now.
Rob