I was talking about *opamp* types that are widely available, not necessarily common circuit designs using them.
No. I talked about the NE5532, a dual opamp with slightly poorer specs than the single NE5534, but with the advantage of a more compact design and wider availability where I live.
Someone suggested this
I agreed with that, except that the claim was that it was not good enough, not "would not work".
NOW I see what's wrong here: Check my post again - the one you're so worked up over. Can't you see that I was talking about the footnote in the link given by Phil Allison, not you? (At the time, I didn't notice that the design itself was by Phil A. I know it now after looking at it again).
You're flaming me because you kept thinking that I was talking about your design, even after Phil A. pointed out your mistake. This makes the rest of your rant irrelevant.
Did you see the place above where I pointed out that you've been attacking me for a totally erronous assumption? Can you finally see that I was talking about Phil A's link and his design (although I didn't know it was his design at the time), NOT yours?
I saw enough to agree with the concept. And the concept is not new to me, as I indicated elsewhere. In fact, I used similar designs in my products more than 20 years ago.
Then perhaps you should take it up with the guy to correct it.
No, I didn't, at first. I noticed it only when I looked again after reading David Eather's rant. But it makes no difference to the technical points, and I made it clear that I was commenting on the footnote, not the main design.
A slight correction: My earlier comments were specifically about the footnote at the end of the page, not the design itself. Turned out, as has now been explained by Phil A., that the footnote was inserted by someone else.
Ah, good old Phil. What would we do without you for entertainment in sed.... Anyway, why would I want to go through it again in minute detail? I've already indicated that I'm familiar with the topology and like it. I already knew that it's capable of excellent performance. I glanced through the salient points and saw nothing to argue about. I have enough experience to come up with my own design without needing to copy yours. I grasped what you were saying about capacitors, regulators, noise, etc.without having to plod through everything word by word, particularly as there's nothing new for me there.
I agree with all of that and, before starting the thread, I briefly considered transformers as one possible solution. But there's one factor that always has to take precedence for me: availability.
In India, true online electronic parts shops are practically non-existent. The two exceptions, the Indian branches of RS and Farnell/element14, sell parts at anywhere from 5 to 100 times the retail prices at OTC shops. I live far from any major city, and while it's sometimes possible to order common parts from these physical shops, it's an exercise in futility to ask for low-demand niche components like a high-quality mic transformer. I'm speaking from over 40 years of frustrating experience. Major suppliers don't bother with retail quantities.
Good points, especially about the stock problem. For example, I may be able to find some mic transformers on one of my occasional visits to the cities, but they are most likely to be of unknown quality and specs, and it's more likely than not that I won't be able to get more of the same type later.
Whats the situation there wrt electronic scrap? Is it a workable option to get a lot of stuff - though likely not specific opamps. I ask as it applies to a lot more than just this thread.
First the notion that a PP3 connector will never contact the wrong way round is unrealistic, IME with this its a high risk event, polarity protection is necessary. Since cost matters, a series diode is cheaper than a fet, and _if_ your opamps have reasonably low minimum psu v, there will be little impact on battery life. If the chosen opamp has relatively high final voltage, a diode would make a big dent, and I'd not do it. Battery voltage/discharge curves will explain why. A parallel diode and fuse introduces a big reliability issue, and I'd hate to foist that on a customer, and a parallel diode alone is a bit of a safety issue, albeit one often chosen. Also a parallel diode can die under the excessive current of a shorted NiMH, and die o/c, leaving the circuit not so well protected.
Oh, 2x9v PP3s gains you close to nothing in battery life, due to the shape of the battery voltage/discharge curve, it simply doubles run cost. Finally on this point, I dont know why you need so many opamp stages, but I'd really try to improve greatly on 40hr battery life if at all practical. As an end user I have little sympathy for designs that gobble batteries in bulk. If your device must eat that much current for some reason, I'd look at the option of using AAs instead.
I dont know what functions you're doing with so many opamps, so I dont know if you might be in a position to replace one or 2 with discrete class A stages to reduce current draw and cost.
Second, it seems that nowhere in this thread have teh bias components been calculated. If max 1/2v bias deviation is acceptable, and max possible bias i is 4uA, then you'd need a 1.1Mohm impedance or less for your bias point, so a pair of 2.2Mohm Rs would be acceptable, and minimise current draw. You'd then add a capacitor to drop the ac impedance considerably. Cap value can be calculated by working out the max acceptable time to reach a usable working voltage, eg 1 second. The value will be very small, and ceramics are the cheapest option, and have good performance at rf, helping to swamp any such pickup. If you need faster 'warm up' and lower ac impedance, you could replace the 2.2M with 2x Rs, and add another cap at that point.
Finally, since cost is an issue, and parts to labour costs far higher in India than here, I'd at least consider marking your cct diag with min and max values and acceptable types for non-critical parts, and using scrap for those.
Out of interest, what sort of PCB are you using there?
any awake person knows some people press on pp3 connectors the wrong way, then when they dont stick turn em round
rechargeables
a) often, yes. You never seen one that split in 2? b) introducing an entirely unecessary shorted diode failure into a product isnt good engineering. Its only fair practice where the V drop of a series diode isnt tolerable.
Ah, I guess those PP3 holders that take the battery either way round dont exist then.
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