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RE: P14 Prototyping Techniques: Attempting to Measure Op Amp Open-Loop DC Gain

colporteur — Thu, 18 Sep 2025 22:30:50 GMT

It is a prototyping technique I would consider trying. It doesn't look pretty but if it gets you the proof of concept results then it has form in my books.

RE: P14 Prototyping Techniques: Attempting to Measure Op Amp Open-Loop DC Gain

Loulou — Mon, 15 Sep 2025 13:56:52 GMT

I have done an OpAmp tester base on this méthod of measurement.

Jean-Louis

RE: Building an IOT power supply - Part1

Yosef12 — Wed, 26 Feb 2025 17:31:51 GMT

Can you describe the IC with 28-pins please? Thanks

RE: Old times

dougw — Sun, 27 Nov 2022 07:01:27 GMT

Very interesting ... although some pictures aren't working anymore.

RE: Temperature gradient PCB

Nareshiyer — Sun, 10 Apr 2022 07:59:42 GMT

A very good article. Kindly accept my kudos.

RE: Temperature gradient PCB

dansmith57 — Sun, 03 Apr 2022 08:22:32 GMT

Nice work! From my own experiments with Peltier modules I find they work much better if water cooled. You can also move the extracted heat away from your experiment.

RE: Temperature gradient PCB

mp2100 — Fri, 25 Mar 2022 18:48:49 GMT

So now I know, you really are a neuromodulator.

RE: Pluggable Module Prototyping for Baluns and other Components

jc2048 — Tue, 22 Mar 2022 10:28:21 GMT

Fair-Rite provide graphs of permeability against frequency for their cores, so I thought it might be interesting to see the difference between the type 43 material (NiZn) of your first core and the type 77 material (MnZn) of your second one.

In case anyone is interested, here I've overlaid the 77 one (black) with the 43 one (red). I'm not wonderful with Gimp, but after a bit of fiddling around I managed to stretch the overlay to fit.

RE: Old times

neilk — Tue, 22 Mar 2022 09:53:36 GMT

Carlo, a great story!

Takes me back to my start in electronics!

Neil

RE: EyeBall Thingy

neilk — Mon, 21 Mar 2022 16:01:30 GMT

Nice bit of fun, Dubbie.

TinkerCad looks useful as well.

Neil

RE: Pluggable Module Prototyping for Baluns and other Components

jc2048 — Sun, 20 Mar 2022 12:04:36 GMT

Interesting experiment. Thanks for blogging about it. I don't have any experience of such things at all (I'll have to buy some suitable ferrite cores and try it for myself). It's even a bit of a struggle getting my head around the theory. The role of the ferrite seems to be quite complicated, doing different things at low and high frequency, so it's nice to see a direct demonstration of how moving the transition between the low-frequency high-permittivity area to the higher frequency 'lossy' area with the two different ferrite materials affects the performance.

Have you tried throwing fast pulses at it and seeing what emerges? If it's truly wideband it should preserve the pulse shape with reasonable fidelity.

RE: Pluggable Module Prototyping for Baluns and other Components

shabaz — Thu, 17 Mar 2022 13:37:38 GMT

This fixed it : )

This is 35 turns of the red and green wire from that pack of 4 bobbins, wound on a different core. It is Fair-Rite 5977000201

Using two of these in the same circuit as before, now I get these results; basically, it is now usable down to 50 kHz or so (with a few degrees phase error as can be seen in the mean phase automated measurement in the 'scope screenshot below; by about 100 kHz the error is down to a degree), but still functions well to 50 MHz and likely higher (I didn't test higher).

RE: Let's Get Twisted

shabaz — Tue, 15 Mar 2022 21:16:34 GMT

Hi Scott,

Nice result : ) Incidentally, I tried figuring out the characteristic impedance of such twisted Kynar wire once, and to me it seemed it was at the very least ballpark 80 ohm, if not dead-on, with a normal amount of twists (maybe 10 twists per inch). I could be wrong so take it with a pinch of salt, but I think it's about right.

This site reckons it is 100 ohms. Which is not too far away from it either.

Also, very nice way to twist them.. I want to try that sometime.

RE: P14 Prototyping Techniques: Attempting to Measure Op Amp Open-Loop DC Gain

jc2048 — Tue, 15 Mar 2022 17:54:32 GMT

I took the advice of Shabaz and increased the amount of attenuation from the integrator output to the input of the
DUT. Rather than increase the 100k further, I decreased the 100R resistors to around 9.6R by putting 10R resistors in
parallel with them (it was easier to do that than pull the SMD 100R resistors off the board). That gets a larger
swing at the integrator output for the 1V change and gives me something I can at least measure, if not very
accurately. I had to increase the resistance in series with the integrator to get it stable for all four of the parts
I was testing. Take these figures with the proverbial pinch of salt, but that gets me measured gains of 944k
(119.5dB), 1039k (120.3dB), 692k (116.8dB), and 577k (115.2dB).

This is what the original datasheet showed for typical figures (I'm measuring with 15V supplies), so they're in the
right ballpark, though somewhat high.

RE: P14 Prototyping Techniques: Attempting to Measure Op Amp Open-Loop DC Gain

dougw — Tue, 15 Mar 2022 16:52:45 GMT

This brings back some memories of a circuit I designed with an amplification of 1 million. I also used OP27s because of their low noise. I had to use low value resistors and multiple stages to minimize resistor noise. Can you just reduce all resistor values by a factor of 10? Maybe try an OP27 as the DUT just to see if you can get better results from a low noise amp. You could also try running it at as cold a temperature as possible because the noise is also lower at lower temperatures.