0.13x vs 1.0x gain op amp regulated power supply - fail - Page 1
Forum section: electronics / projects

author: HendriXML
author_rank: Super Contributor
timestamp: February 13, 2019, 01:53:28 pm
content: Hi,I did some characterization of a IRLZ44N via a power supplyhttps://www.eevblog.com/forum/testgear/this-graph-brings-tears-to-my-eye/msg2190639/#msg2190639.Did also some curve fitting and came to the hypothesis that it should be possible to drive such a reactive component with very low gain. Here is an ongoing little experiment in which I will examine the possibilities.First about the schematics:It is essentially a differential 1 gain amplifier, with the reference voltage at the gate! To keep it from being a fast positive feedback, there is are a few capacitors to suppress that from happening. Given more time the ref voltage settles and Vsg become about the same.What are the benefits of this solution compared to high gain feedback ones?There is/should be less overshoots. There's no (relatively) large inrush current to the Mosfet gate (the gate capacitance), because this will be smoothed by a short and fast feedback loop (via R4). Resistor R12 which kind of separates the loops is therefore critical. At first I didn't have this resistor in the circuit and the outcome was rubbish.The negatives of the circuit I will explore. It probably drops in voltage with a very sudden increase in current. Like going from 1mA to 1A. I’ll do some measurement later on.It’s uses also quite some idle current because of the Zener diode reference voltage.One of the attachments shows the noise while driving a DC low RPM motor at 700mA.Feel free to discuss and comment on this experiment. (I will eventually use it as a 5 x AA battery to 5V regulator). It is with persistence on, so a 5 sec representation of the noise.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 13, 2019, 03:58:38 pm
content: The amplifier (e.g. OP) is only one of the noise sources in the voltage regulator. It may be relevant at higher frequencies.The other important noise source is the voltage reference itself, especially at lower frequencies, as essentially all voltage references have quite some 1/f noise.In the current circuit there is a resisive divider (:2) and the relatively large resistors (47 K that add to the noise - so it would not be very low noise).The circuit uses an output stage that controls the current (the MOSFET controls the current via the gat voltage). Because of the rather high trans-conductance of the MOSFET, the overall loop gain may not be that small. The rather simple loop structure with mainly the output capacitor as the bandwidth limiting part may work well with some loads, but may not work well with other loads. The MOSFET is also rather nonlinear and will respond stronger at high current. So the response is to be expected very slow at low current and may be acceptable (and possibly to fast resulting in oscillation) at high current.The ESR of the output capacitor can have quite some effect on the response - too little may be a bad idea.

author: HendriXML
author_rank: Super Contributor
timestamp: February 13, 2019, 04:41:31 pm
content: Quote from: Kleinstein on February 13, 2019, 03:58:38 pmHi, thanks for reacting!In the supplied link I did some measurements on the Mosfet voltage rise on source-drain vs needed Vgs compensation ratio.What came out of the graph that the regulation of current might not lineair, the voltage rise isn’t as well. If one compares them then the compensation ratio seems not that widely spread.I spoke of noise, but I mean all the stuff you don’t want on the output.From what I’ve seen it does a great job, but I wouldn’t know how to do a proper benchmark. I know for example the output is cleaner than that of my bench power supply. But it’s got longer leads to the DC motor load.The posts are also about how to investigate things (with limited means) and learn from the comments.I guess power supplies are a great way of doing this kind of exploration.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 13, 2019, 05:34:15 pm
content: A voltage regulator looks like a simple beginners circuit and it kind of still is. However when looking at the theory behind it a voltage regulator can be quite a complicated beast, one can write books about. There is a lot of theoretical background that may be needed to really understand it in detail. If one really understands a lab supply it something like half way to the EE degree.For the "noise" one normally uses this word for the noise coming from the regulator when used with a simple resistive or similar well behaved load. The extra AC part seen with a more nasty load like a DC motor is normally described with by the output impedance. So how much change in output voltage when the load current changes. So it is more about applying an AC current (superimposed to the DC load) and measuring the AC voltage.For doing this one frequency at a time it would need something like a function generator and a Lockin amplifier or similar instrument. The voltage may well be to small to directly measure with the scope - though with a simple not that good regulator the scope may be sufficient.The more common test is in the time domain, looking at the step response when the load current changes from something like 10% to 60% of the nominal load (The load levels vary - not sure there is kind of standard case) and back. Ideally this may need a special switchable load. With a modern DSO to measure one may get away with just 2 resistors and a suitable switch / relay. Some older lab supplies (e.g. 1960s-1970s) use such curves to show there performance. It is still a good test.

author: HendriXML
author_rank: Super Contributor
timestamp: February 13, 2019, 06:00:37 pm
content: Quote from: Kleinstein on February 13, 2019, 03:58:38 pmOne thing I’ll try to realize is that better specs don’t alway perform better. Voltage needs to drop (maybe a tiny bit) to get a regulation happening.A capacitor that withstands a voltage drop, also withstands a compensatory voltage rise. One thing I was a bit disappointed in was that the circuit needs a capacitor (a 330uF was good as well). But I did take the best I could find and even measured it having a low esr. So something to keep in mind.My other designhttps://www.eevblog.com/forum/projects/bi-regulated-power-supply/seems not to need one.

author: HendriXML
author_rank: Super Contributor
timestamp: February 13, 2019, 06:13:21 pm
content: Quote from: Kleinstein on February 13, 2019, 05:34:15 pmI was thinking of using another mosfet in series with different load resistors and saturate it with a square wave signal, and see how it goes. The question I want to answer is what range it can regulate without significant drops. Somehow I think the integration of the ratio curve in the other post has a relation to it. My thoughts are if it’s less than 1 (or 0.5 because of the resistive divider), it’s okay. If its more, the reference capacitor needs to charge a bit further, so the output voltage will drop.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 13, 2019, 06:52:30 pm
content: There are mainly 2 types of voltage regulators:1) Regulator and power stage which control the output current. Usually the output is from the drain or collector of the power fet / transistor. The circuit here is such an example. These regulators essentially need an capacitor at the output and often quite some size.2) Regulators with a low output impedance power stage, like an emitter follower or source-follower. Here one can get away without a capacitor at the output, though many circuits still use a relatively small capacitor to get better performance at higher frequency.The gain of the differential amplifier is from the input voltage to the gate voltage. This is followed by the voltage gain of the mosfet, that depends on the trans-conductance of the FET and thus the current and the load seen at the output. So there is nothing special about the gain of 1 or 0.5 for the first stage. The capacitor at the output makes sure the gain of the output stage (= MOSFET with load) will go down about like 1 over frequency towards higher frequencies. For this reason the capacitor is essentially needed.The regulator circuit from the other thread looks like a real mess, much like a typical beginners try and error circuit, that might for some odd reason kind of work under some conditions, but several points that make one think how the heck could this work. The circuit here looks much better.

author: HendriXML
author_rank: Super Contributor
timestamp: February 13, 2019, 08:33:09 pm
content: Quote from: Kleinstein on February 13, 2019, 06:52:30 pmMy main purpose isn’t to make a power supply, but to test idea’s to let my knowledge about this stuff grow. I really like the other one a bit better, it makes me smile thinking about it.. I know it’s horrific to professional standards and shouldn’t be used other than in an experimental/supervised situation. But that’s also not the intended angle to look at it.But I’m indeed just starting and lacking a lot of insight, doing experiments and sharing those is a fun way to increase it. In my experiments I try to focus on only a few elements - discarding others I know and even more I don’t know and hoping to get some surprising result.

author: HendriXML
author_rank: Super Contributor
timestamp: February 13, 2019, 09:04:50 pm
content: Quote from: Kleinstein on February 13, 2019, 06:52:30 pmTo my understanding such a low gain in the first stage can only work if there’s some offset or voltage lift towards the Mosfet gate. Any idea how this normally is implemented/controlled?Gain is one way to look at it, but in reality nothing is amplified (like a voltage follower). So the way I also thought about it was there is a short and a long feedback loop. One before the Mosfet gate being fast without capacitance/inductance problems and one a bit slower through the Mosfet making the balancing more controlled because of the other short loop. Does that make any sense?

author: HendriXML
author_rank: Super Contributor
timestamp: February 13, 2019, 11:33:19 pm
content: Did some measurement with a signal generator driving a Mosfet which pulls a resistor low.The measurements (peak to peak) are down below:ResistorSiglent powersupplyMy circuit5R12.68 V0.59 V6R81.84 V0.48 V10R1.52 V0.36 V15R1.36 V0.26 VMy circuit also restores the voltage a bit faster in time. I didn't expect that my circuit would do so wel under such a sudden load.The green line is the signal to the Mosfet gate from the generator, which isn't the fastest thing around (also 50 ohm output).

author: HendriXML
author_rank: Super Contributor
timestamp: February 13, 2019, 11:47:03 pm
content: Quote from: HendriXML on February 13, 2019, 06:13:21 pmFrom the measurements done above this does not seem the case.That raises also the question about how important the raising of the ref voltage is.Or wether it is possible to drive the Mosfet with even lower "gain".To bad I've soldered the resistors down so that isn't just a quick check. The legs are also the traces...perfboard experimenting issue.

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 01:10:01 am
content: I wanted to make sure that the constant current mode of the Siglent had no part in the voltage drop, so I did new measurements with the CC up to max (3.2 A)ResistorSiglent powersupplyMy circuit5R12.08 V0.60 V6R81.90 V0.50 V10R1.62 V0.40 V15R1.36 V0.30 V

author: xavier60
author_rank: Super Contributor
timestamp: February 14, 2019, 01:25:52 am
content: It looks like you are using positive feedback to increase gain at DC and low frequencies?

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 01:42:42 am
content: Quote from: xavier60 on February 14, 2019, 01:25:52 amYes but with some delay. The idea is that it settles on a value so that a even a little effort of the “diff amp” has still some effect. To keep the volts/sec low.

author: xavier60
author_rank: Super Contributor
timestamp: February 14, 2019, 01:59:46 am
content: An op-amp configured as a non-inverting amplifier with a feedback capacitor from the op-amp's output to inverting input will give the same result plus even more gain at DC. This will reduce the regulators steady state output voltage error to less than a millivolt if the layout is done right.BTW, your output stage is current sourcing into a capacitor. For the feedback loop to be stable in this situation, the error amplifier(op-amp) needs to have some proportional gain. An op-amp configured as mentioned above has a gain that can only drop to one at higher frequency. This is well suited.

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 10:30:20 am
content: Quote from: xavier60 on February 14, 2019, 01:59:46 amI think I understand most of what you say, but just to be sure I made a schematic. Will also use that to think things through and see the benefits. Losing the positive feedback is probably one of them. The change has some "double inversion" (low band -> highband, positive fb -> negative fb) to it, so it will probably change some characteristics too.

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 11:14:03 am
content: Looking at the schematics I think you mean loosing the diff-amp stuff too, like so.

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 11:49:59 am
content: Quote from: HendriXML on February 13, 2019, 09:04:50 pmI think the proposed schematics answers that question. Saves a lot of resistors.

author: xavier60
author_rank: Super Contributor
timestamp: February 14, 2019, 12:00:10 pm
content: A balanced input amplifier would be useful possibly for sensing voltage at the output terminals. I haven't given it much thought though and I have never been able to justify the need in the power supplies that I have built.

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 01:52:35 pm
content: One difference in the proposed schematic is that the capacitor is now sourced via R5. So a sudden increase in the supply voltage, might pull on the gate wouldn’t it? A phenomenon which has to be regulated, and might have effects on the output.

author: xavier60
author_rank: Super Contributor
timestamp: February 14, 2019, 02:09:48 pm
content: Quote from: HendriXML on February 14, 2019, 01:52:35 pmYes, fluctuations of the input voltage will disturb the regulation. With the so called "floating type" regulator topology, all of the control circuitry is referenced to the MOSFET's Source which is also the positive output terminal. But it requires the extra floating rails to power the control circuitry.

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 02:23:48 pm
content: Quote from: xavier60 on February 14, 2019, 02:09:48 pmThis all pulls a bit hard on me brain, ha ha.One possitive aspect of the initial schematic might thus well be that the “offset” is more tied to the ground/source.

author: xavier60
author_rank: Super Contributor
timestamp: February 14, 2019, 02:42:38 pm
content: Quote from: HendriXML on February 14, 2019, 02:23:48 pmThat is a bit tricky to nut out. I often see in high performance supplies a conventional 4 resistor balanced amplifier to sense the rail voltage and scale it down. This scaled down voltage and reference voltage is fed into another op-amp functioning as the error amplifier. All of this can be referenced to the MOSFET's Source pin.I hope I have that right.

author: xavier60
author_rank: Super Contributor
timestamp: February 14, 2019, 02:51:31 pm
content: Also, the op-amps won't have to be powered at the full input voltage.The balanced amplifier would need to have near perfect CMRR to prevent input voltage variations affecting regulation voltage.

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 06:25:56 pm
content: Quote from: Kleinstein on February 13, 2019, 03:58:38 pmThis is something I'm tried to find out in the supplied thread and if I'm not mistaken (maybe someone is willing to verify that?) more amplification is needed at higher currents. The Mosfet becomes more sensitive, but the voltage (source-drain) raise/amp decreases faster.I will test the initial circuit with minimal gain using the graph: 1/4 from the diff. amplifier * 1/2 from the divider. 1/8 should still work. Maybe then we'll also see a larger voltage drop at a sudden load.

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 07:34:10 pm
content: I could just fit 2x parallel resistors of 15K. Without desoldering the previous ones.The new results amaze me! The response has improved a lot! Wasn't expecting that.-- So I verified the test setup.... no magic to be seen here..My circuit 2 not saturated!0.13 V0.12 V0.10 V0.08 V

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 07:47:53 pm
content: Hmm made a mistake with the signal generator in these test runs: the load Mosfet did not become saturated..The table with comparable conditions is:ResistorSiglent powersupplyMy circuitMy circuit 25R12.08 V0.60 V0.78 V6R81.90 V0.50 V0.65 V10R1.62 V0.40 V0.48 V15R1.36 V0.30 V0.29 VIt's worse as one would expect, but not much! With less amps its on par.

author: HendriXML
author_rank: Super Contributor
timestamp: February 14, 2019, 08:47:31 pm
content: So I altered the circuit to have the lowest gain possible (by looking at the curve). Now I wanted to check whether it could go without an endcap (C7): it now seems to be stable at resistive and inductive loads.I attached some scope images to show how it responds to sudden loads. It’s not good (the scales are very different!) but it stabilizes nicely.These results should be discarded, reason down below.

author: HendriXML
author_rank: Super Contributor
timestamp: February 15, 2019, 12:44:14 pm
content: I was doing some measurements and things didn't add up. Because of the better resolution I did the measurements in AC mode. But sometimes that hides stuff you would like to know. One thing that would have shown otherwise was that the capless measurements were taken when the circuit did not regulate properly. One of mod resistors had a loose contact.The other measurements after the mod, seem to be fine. I did some retesting and got even (a bit) better results.But this thread was not started to make the world’s finest supply, it is mostly about a circuit which can give some insight in how to model the amplification of a IRLZ44N. Because it was at first not stable without a cap, the needed measurement could not be done. I'm optimistic that there's now a situation in which some interesting conclusions can be draw. There're probably books which provide much better information. But this is more fun.Back to the –regulated- capless response:I posted 2 curves, the difference are the reference caps (C1, C4, C5, C6). The first one is with C4, C5, C6 on board, thus 300nF. The second is with only C4, thus 100nF.It is clearly to see the caps need to charge up before a new balance is found. This takes about 200us per 100nF. Because that is a relatively long time, I’ll assume the ref voltage as being constant, when analysing the first few us. This will be done in following posts, but it might take a while.Image 005 shows 2 curvesGreen: the drain of the pull down (load) MosfetYellow: VCC outThe difference between those is the voltage over a 5R1 resistor and should give us the current drawn at each moment. Will make some graphs to show this more clearly!

author: HendriXML
author_rank: Super Contributor
timestamp: February 15, 2019, 12:52:11 pm
content: Quote from: HendriXML on February 13, 2019, 11:47:03 pmMy initial "hypothesis" might still be correct! The endcap had such a huge impact, that no conclusions could be drawn. If the integration/integral stuff seems to be true, then I should somehow incorporate that in my "mental model" of "amplification". A empirical answer needs probably also some more (advanced) testing. Maybe one of you already knows a theoretical one?The question is - given the curves in the posting below- how much gain is needed to keep a steady Vsd (and Vout from not dropping) in a given range of Vsg (which corresponds to a initial amperage - new amperage). Without the effect of the "delay" of the amplification/sensing, so keeping time out of the picture.https://www.eevblog.com/forum/testgear/this-graph-brings-tears-to-my-eye/msg2189625/#msg2189625

author: HendriXML
author_rank: Super Contributor
timestamp: February 15, 2019, 06:07:00 pm
content: Made the current graph (purple, right axis).It shows that initially a small change in current, means a large drop in the output voltage. This because the initial Vsg results in a high Rsd resistance (about 2k). In this regard resistance means voltage rise/amp (-> output drops). A tiny 1 mA would thus mean a 2V rise! But Vsg is regulated and climbs, but it's clearly not enough:This can be caused by at least 2 effects:The gain (sensing Vout drop -> rising Vsg) is to lowThere's a delay (between sensing en responding)Anybody any ideas?Will (also) try to unravel the problem myself.

author: HendriXML
author_rank: Super Contributor
timestamp: February 15, 2019, 11:08:13 pm
content: I think I found a way to unravel the mystery of what gain is needed when an "amperage jump" is made.Will do that in the other thread.https://www.eevblog.com/forum/testgear/this-graph-brings-tears-to-my-eye/msg2203539/#msg2203539

author: HendriXML
author_rank: Super Contributor
timestamp: February 17, 2019, 05:19:34 pm
content: Quote from: xavier60 on February 14, 2019, 02:51:31 pmWhen I was done experimenting, I thought why not see wether this circuit can operate on an adapter. The adapter is about 9V and I added 2 smoothing capacitors of 2200uF.The result was that the output became very “noisy” with loads, I don’t think there’s even a repetition going on.So as an experiment and a way to check out idea’s it did a good job. But as a proper supply I would call it a fail.As a battery voltage dropper its probably ok, I will have to check that. But I think its going to be recycledCould you give an advise on an op amp which can regulate well on about 5-7 V, without being to sensitive to variations? Would be nice if it is THT and can be bought on AliExpress. But I wonder if it’s not the time get stuff elsewhere.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 17, 2019, 08:54:35 pm
content: The circuit has a more general problem than just finding a suitable OP. I think it would be a good idea to take a step back and look at other, more normal voltage regulator circuits or read some more about the theoretical background.Electronic systems with feedback can be quite complicated to understand - the theoretical background is only from the first half of the 20th century - so much of it is less than 100 years old. I don't know your mathematical background - so it's hard to give a suitable way learn about it.It would probably help to start with something like stability in OP circuits. The simplest rule of thumb I know is aiming for a system that is slow at only one point and fast everywhere else. This leads to the simple case of dominant pole compensation.For simple test on the bread board, I would keep it relatively slow, so OPs with a GBW of something like 0.3 - 2 MHz. Though not ideal the LM358 is a good start for a voltage-regulator on the bread board.

author: HendriXML
author_rank: Super Contributor
timestamp: February 17, 2019, 10:20:57 pm
content: Quote from: Kleinstein on February 17, 2019, 08:54:35 pmThanks for the response, the LM358 seems a good one to experiment with.As for my background, I’ve got me brain damaged, so I’m somewhat limited in my abilities to learn/comprehend stuff and the math stuff I did know has become a bit vague. So I’m just fine by doing experiments and to see how an idea turns out. As in this case: as a supply it may have failed. But checking my understanding about voltage rise/drop sensing and needed gain as an experiment was for me a success. If I now read something about this stuff I can link it to this practical experience (with blog!).

author: xavier60
author_rank: Super Contributor
timestamp: February 17, 2019, 10:42:24 pm
content: Quote from: HendriXML on February 17, 2019, 05:19:34 pmI went through the same process a while back, trying my own ideas and failing because I didn't know enough to understand the challenges involved.I settled on the well known floating type topology and successfully completed a bench supply projectAlthough the performance is good, I found debugging to be awkward, having to take measurements with respect to the positive output terminal.The LM358 is more than good enough for experimenting. It operates from 3 to 36 volts. One important op-amp parameter to be aware of is the input common-mode range. It includes ground voltage for the LM358 which can be very useful in certain applications.You will lean a lot from data PDFs.Are you just experimenting or intending to construct something?

author: HendriXML
author_rank: Super Contributor
timestamp: February 18, 2019, 12:04:00 am
content: Quote from: xavier60 on February 17, 2019, 10:42:24 pmJust experimenting yet, at least until I got some “model” of how the components really work. On the way it is nice to end up with something that works, at which you can look back at. I already have a fume extracter for instance which I’m happy about. It’s starts when the you take the iron out of the stand, and it keeps blowing for a while after you put it back. This gives the smoke time to travel through a ventilation hose ending outside. In practice I don’t use the hose, but its much better than nothing. It has also dimmable LED’s (variable current).Even used diffusion sheet to have less reflection on those tinned area’s.I was making some boxed modules with logic gates, LED output, switches and stuff for my son (9) to play with. But he’s not really attracked to it. I think as a toy it needs to look more simple with only the printed symbols, ins and outputs. The prototypes are with lot of transistors, no ic’s.For safety I want it battery powered, so if the circuit drops the voltage in a stable way I might use it. But I may also drop the whole idea. He plays this game Scrap Mechanic where he can do “virtually” much more cool stuff. And I don’t see any reason why playing with the boxes I (would) made would be more fun. Times have changed.

author: HendriXML
author_rank: Super Contributor
timestamp: February 19, 2019, 01:11:18 pm
content: About the circuit: the next time I will use a larger perf board. Also first deciding which components might be swapped and use pinheaders for them. Using dupont female connecters to make those components swappable or directly solder them on the pins.On breadboard's I've got mixed feelings. If you've got cheap resistors they are a bit loose (I bend them, doubling the thickness) adding components on heatsinks is also somewhat complicated.

author: HendriXML
author_rank: Super Contributor
timestamp: February 19, 2019, 08:53:00 pm
content: Quote from: HendriXML on February 17, 2019, 05:19:34 pmI replaced the Mosfet, and indeed the strange noise went away. The circuit was somewhat stable using an adapter, but had a 100 hz ripple. Possibly the op amp needs a stable powersource. The used op amp is also not very suited for the usage, but I had it laying around.Using a C1 capacitor: 10 nF made the circuit oscillate. 4.4 nF was OK, but did not enhance the performance.So I won’t post any more graphs.Working with header pins and dupont connectors worked fine. Having a wire with one dupont connecteron it makes it much easer to place header pins and keep them steady while soldering. The wire can for instance go down in another hole adding some pull to the pin.

author: HendriXML
author_rank: Super Contributor
timestamp: February 19, 2019, 09:26:06 pm
content: Some conclusions that I draw from this adventure:A programmable power supply can be used to automate characterizationExcel can make good graphs, giving the possibility to combine more traces and or do more complex math between themUsing XML as a data format worked nice and fast. No asking for headers, data types etc. if you supply a XML schema.Maxima can be used to make graphs as well, can be saved as PNG or SVG, but doesn’t need Visio for that. It has less options to change the appearance.Maxima can be used to fit curves, having some idea of what function it should match with is important.The website zunzun.com can do curve fitting also, and has a lot of possibilities and also gives a functionWhen using low gain error amplification it is important to not let the gate capacitance disturb the short feedback loop. However this also means sacrificing in gate drive speed.In a low current situation the Mosfet as a high Rsd resistance. Voltage drops are huge with only a small change in current. Because of the gate capacitance changing to a low resistance state takes some few 100ns of time. A end capacitor can slow down the voltage drop a bit, giving the circuit more time to adapt.The first stage gain needed to adapt is low, it even works with 0.13x gain, but no real advantages where found doing this. Except it was more stable without a endcap. However this situation was unusable.Even powermosfets can easily be zapped.Better to choose a large perf board, keeping space for modificationsUsing headers and dupont connectors to add swappable components worksDon’t underestimate the usability of BJT’sA lm358 is a good and affordable op amp to experiment withThere’s a difference in having a working concept and a working product. Both should be celebrated!